Maharashtra Board Class 9 Science Chapter 13 Carbon An Important Element Solutions

Std 9 Science Chapter 13 Carbon: An Important Element Question Answer Maharashtra Board

Class 9 Science Chapter 13 Carbon: An Important Element Question Answer Maharashtra Board

Question 1. Select the proper option and complete the statements (single, all, double, ionic, carbon, give and take, hydrogen, multiple, share, most, covalent)

Answer:
(a) A carbon atom forms a covalent bond with other atoms. In this bond the two atoms share electrons.
In simple words: Carbon atoms share electrons to form covalent bonds with other atoms, resulting in stable compounds.

🎯 Exam Tip: Understanding covalent bonding and electron sharing is crucial for questions on carbon compounds.

Question 1. Select the proper option and complete the statements (single, all, double, ionic, carbon, give and take, hydrogen, multiple, share, most, covalent)

Answer:
(b) All the carbon bonds in a saturated hydrocarbon share electrons.
In simple words: In saturated hydrocarbons, all carbon atoms form single covalent bonds by sharing electrons.

🎯 Exam Tip: Key terms like 'saturated' imply single bonds, which is a fundamental concept for hydrocarbons.

Question 1. Select the proper option and complete the statements (single, all, double, ionic, carbon, give and take, hydrogen, multiple, share, most, covalent)

Answer:
(c) At least one carbon bond in an unsaturated hydrocarbon is multiple.
In simple words: Unsaturated hydrocarbons contain at least one double or triple bond between carbon atoms.

🎯 Exam Tip: Differentiating between saturated (single bonds) and unsaturated (multiple bonds) is a core concept for classifying hydrocarbons.

Question 1. Select the proper option and complete the statements (single, all, double, ionic, carbon, give and take, hydrogen, multiple, share, most, covalent)

Answer:
(d) Carbon is the essential element in all the organic compounds.
In simple words: Carbon is the foundational element for all organic compounds due to its unique bonding capabilities.

🎯 Exam Tip: Remember that organic chemistry is essentially the study of carbon and its compounds.

Question 1. Select the proper option and complete the statements (single, all, double, ionic, carbon, give and take, hydrogen, multiple, share, most, covalent)

Answer:
(e) The element hydrogen is present in all organic compounds.
In simple words: While carbon is central, hydrogen is almost always present in organic compounds, making them hydrocarbons or their derivatives.

🎯 Exam Tip: Most organic compounds are based on a carbon-hydrogen framework, even if other elements are also present.

Question 2. Answer the following questions

Question 2.a. Why are carbon and its compounds used as fuels?

Answer:
(i) The name 'carbon' is derived from Latin word 'carbo'meaning coal. In the earth's crust, carbon is present to an extent of approximately 0.27% in the form of carbonate, coal and petroleum. One of the non-crystalline and amorphous form of carbon is coal. Coal is a fossil fuel.
(ii) Peat, lignite, bituminous and anthracite are the four types of coal in the increasing order of their carbon content and heat produced respectively. Charcoal and coke are the other amorphous forms of carbon used as fuel.
(iii) Compounds of carbon such as hydrocarbons consist of carbon and hydrogen and they are easily combustible. For example, methane (CH\(_{4}\)) which occurs in natural gas is highly inflammable. It burns by reacting with oxygen to give a bluish flame. In this reaction, 213 Kcal/mol of heat is given out. Methane burns completely.
Chemical reaction: \[\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O} + \text{Heat}\]
(iv) Thus when hydrocarbons are burnt in air, large amount of heat is evolved with formation of carbon dioxide (CO\(_{2}\)) and water (H\(_{2}\)O). Due to evolution of heat on combustion, carbon and its compounds are used as fuels.
In simple words: Carbon and its compounds, primarily hydrocarbons, are excellent fuels because they are highly combustible, releasing a large amount of heat energy upon burning. This heat evolution makes them valuable for various energy needs.

🎯 Exam Tip: Focus on the high energy release (combustibility) and the products of combustion (CO2 and H2O) as the main reasons for their use as fuels.

Question 2.b. In which compound forms does carbon occur?

Answer:Carbon in its combined state exists as various compounds such as:

• Carbon dioxide and in the form of carbonates such as calcium carbonate, marble, calamine (ZnCO\(_{3}\)).
• Fossil fuel - coal, petroleum, natural gas.
• Carbonaceous nutrients - carbohydrates, proteins, fats.
• Natural fibres - cotton, wool, silk.
• Hydrocarbons - compound of carbon and hydrogen.

In simple words: Carbon is found widely in nature, not just as a free element, but also combined in many compounds like carbon dioxide, carbonates, fossil fuels, nutrients, and natural fibers.

🎯 Exam Tip: Be prepared to list various natural occurrences of carbon, distinguishing between its free and combined forms.

Question 2.c. Write the uses of the diamond.

Answer:Uses of diamonds are:

• Diamonds are used in glass cutting and rock drilling machines.
• Diamonds are used in ornaments.
• Diamond knives are used in the eye surgery.
• Diamond dust is used for polishing other diamonds.
• Diamond is used to make windows giving protection from radiation in space and in artificial satellites.

In simple words: Diamonds are highly versatile due to their extreme hardness, making them useful in cutting tools, surgical instruments, polishing, and even radiation protection, in addition to their aesthetic use in ornaments.

🎯 Exam Tip: Remember that diamond's exceptional hardness is the key property enabling many of its industrial uses, besides its beauty.

Question 3. Explain the difference:

Question 3.a. Diamond and graphite.

Answer:

Diamond	Graphite
(i) Diamond is a brilliant, hard and crystalline allotrope of carbon.	(i) Graphite is a black, soft, brittle and slippery crystalline allotrope of carbon.
(ii) In diamonds, every carbon atom is bonded to four neighbouring atoms by covalent bonds forming tetragonal three dimensional structure which makes it very hard.	(ii) In graphite, every carbon atom is bonded to three other carbon atoms by covalent bonds in such a way that a hexagonal layered structure is formed. A graphite crystal is made of many such layers of carbon atoms. These layers slip over each other on applying pressure.
(iii) Density of diamond is 3.5 g/cm³.	(iii) Density of graphite is 1.9 to 2.3 g/cm³.
(iv) Diamond is a bad conductor of electricity as it does not have free electrons.	(iv) Inside each layer of graphite, free electrons move continuously within the entire layer. Hence, graphite is a good conductor of electricity.

In simple words: Diamond is very hard, brilliant, and non-conductive due to its compact 3D structure, while graphite is soft, slippery, black, and conductive because of its layered hexagonal structure with free electrons.

🎯 Exam Tip: Focus on the structural differences (3D tetrahedral vs. 2D hexagonal layers) as the primary reason for their contrasting physical properties like hardness and conductivity.

Question 3.b. Crystalline and non-crystalline forms of carbon.

Answer:

Crystalline forms of carbon	Non-crystalline forms of carbon
(i) A crystalline form has a regular and definite arrangement of atoms.	(i) A non-crystalline form does not have a regular and definite arrangement of atoms.
(ii) They have high melting points and boiling points.	(ii) They have low melting points and boiling points.
(iii) A crystalline form has a definite geometrical shape, sharp edges and plane surfaces.	(iii) They are amorphous, hence, they do not have definite geometrical shape.
(iv) Diamond, graphite and fullerene are different crystalline forms of carbon.	(iv) Coal, charcoal and coke are different noncrystalline/amorphous forms of carbon.

In simple words: Crystalline carbon forms have an ordered atomic structure, definite shape, and high melting points, whereas non-crystalline (amorphous) forms lack this regular arrangement, have no definite shape, and possess lower melting points.

🎯 Exam Tip: The key differentiator is the 'regular arrangement of atoms' which dictates the physical properties of crystalline forms, while amorphous forms lack this order.

Question 4. Write scientific reasons

Question 4.a. Graphite is a conductor of electricity.

Answer:

• In graphite, each carbon is bonded to three other carbon atoms in such a way that a hexagonal layered structure is formed.
• Due to this structure, graphite has free electrons available.
• These free electrons move continuously within the entire layer.
• Hence, graphite is a good conductor of electricity.

In simple words: Graphite conducts electricity because its unique layered structure leaves one valence electron per carbon atom free to move throughout the layers.

🎯 Exam Tip: The presence of "free electrons" is the critical point to mention when explaining why graphite conducts electricity.

Question 4.b. Graphite is not used in ornaments.

Answer:

• Graphite is a black, soft, brittle and dull form of carbon.
• It is neither malleable nor ductile.
• These properties of graphite make it unsuitable for making of ornaments.
• Hence, graphite is not used for making ornaments.

In simple words: Graphite is unsuitable for ornaments because it is soft, brittle, dull, and black, lacking the hardness, brilliance, and malleability required for jewelry.

🎯 Exam Tip: Focus on the physical characteristics (softness, brittleness, dullness) that make graphite undesirable for aesthetic uses like ornaments.

Question 4.c. Limewater turns milky when CO2 is passed through it.

Answer:

• Limewater traditionally means a weak solution of the alkali calcium hydroxide Ca(OH)\(_{2}\).
• When CO\(_{2}\) is passed through limewater, it reacts with calcium hydroxide to form insoluble particulates (precipitate) of Calcium carbonate (CaCO\(_{3}\)).
• Calcium carbonate is weak basic salt and this gives a milky white precipitate.
• Hence, lime water turns milky when CO\(_{2}\) gas is passed through it.

In simple words: Limewater (calcium hydroxide) turns milky when carbon dioxide is passed through it because it reacts to form insoluble calcium carbonate, which appears as a white precipitate.

🎯 Exam Tip: The formation of insoluble calcium carbonate (CaCO3) precipitate is the key chemical reaction to remember for this observation.

Question 4.d. Biogas is an eco-friendly fuel.

Answer:

• Biogas is formed by the decomposition of animal dung, dry leaves, wet garbage in a biogas plant.
• This produces methane gas also called biogas.
• Biogas is a very cheap fuel option which meets the demand for cooking gas.
• Biogas is eco-friendly as it contains about 55% to 60% of methane and rest is carbon dioxide, hence, on combustion it does not produce harmful gases which cause pollution.
• Biogas is a fuel which is convenient to use and in addition to this it produces a very good manure as a side product of the process.
• Hence, biogas is an eco-friendly fuel.

In simple words: Biogas is eco-friendly because it's produced from organic waste, primarily methane, and its combustion releases fewer harmful pollutants compared to fossil fuels, also yielding valuable manure.

🎯 Exam Tip: Highlight the sustainable source (organic waste), lower pollution during combustion, and the production of useful byproduct (manure) as key points for its eco-friendliness.

Question 5. Explain the following.

Question 5.a. Diamond, graphite and fullerenes are crystalline forms of carbon.

Answer:

• Carbon exhibits a property of allotropy in which an element exists in more than one form in nature.
• The chemical properties of these different forms are the same but their physical properties are different.
• Carbon exists in crystalline as well as non-crystalline (amorphous form).
• Crystalline form has a regular and definite arrangement of atoms. They have high melting points and boiling points.
• A crystalline form has a definite geometrical shape, sharp edges and plane surfaces.
• Carbon has three crystalline allotropes such as diamond, graphite and fullerene.
• In the structure of diamond, every carbon atom is bonded to four neighbouring atoms by covalent bonds.
• Therefore, diamond has a tetragonal three dimensional structure which makes it very hard.
• Brilliant and pure diamond is the hardest natural substance.
• In the structure of graphite, every carbon atom in graphite is bonded to three other carbon atoms in such a way that a hexagonal layered structure is formed.
• A graphite crystal is made of many sheets or layers of carbon atoms.
• These layers slip over each other on applying pressure. One layer of graphite is called graphene.
• Fullerene is rarely found in nature. It is found in soot and in interstellar space.
• The first example of fullerene is Buckminster fullerene (C\(_{60}\)).
• This allotrope of carbon is named fullerene after the architect.
• Richard Buckminster Fuller because the structure of C\(_{60}\) resembles the structure of the geodesic dome he designed.
• (xi) Molecules of fullerenes are found in the form of buckyballs and buckytubes.
• (xii) There are 30 to 900 carbon atoms in one molecule of a fullerene., C\(_{60}\), C\(_{70}\), C\(_{76}\), C\(_{82}\) and C\(_{86}\) are other examples of fullerene. Their molecules occur in small numbers in soot.

In simple words: Diamond, graphite, and fullerenes are crystalline forms of carbon, meaning their atoms are arranged in a regular, ordered pattern, leading to distinct physical properties despite sharing the same chemical element.

🎯 Exam Tip: Emphasize 'allotropy' and the 'regular arrangement of atoms' as the defining characteristics of these crystalline forms.

Question 5.b. Methane is called marsh gas.

Answer:

• Methane is formed by the decomposition of plant and animal matter in swamps or marshy areas.
• As methane gas bubbles out from marshy area, it is called as marsh gas.

In simple words: Methane is called marsh gas because it naturally forms from the anaerobic decomposition of organic matter in waterlogged, marshy environments, often seen bubbling out from such areas.

🎯 Exam Tip: Connect the origin of methane from decaying organic matter in 'marshy areas' directly to its alternative name, 'marsh gas'.

Question 5.c. Petrol, diesel, coal are fossil fuels.

Answer:
(i) A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms. Fossil fuels contain high percentage of carbon. The word carbon is derived from the Latin word 'Carbo' meaning coal.
(ii) Coal is formed from the remains of trees and other vegetation. Approximately 350 million years ago, these remains were trapped on the bottom of swamps, accumulating layer after layer and creating a dense material called peat. As this peat was buried under more and more ground, the high temperature and pressure transformed it into coal.
(iii) Petrol and diesel are obtained from mineral oil. Mineral oil also called as crude oil or petroleum oil is formed from the remains of plants and animals that lived in the seas millions of years ago. This plant and animal matter has been drawn down and subjected to extremes of temperature and pressure over millions of years ago.
(iv) Mineral oil is commonly formed in rocks under the sea bed. The word petroleum is derived from Latin word 'Rock oil'. Petrol and Diesel are obtained from mineral oil by the process called as fractional distillation. Thus petrol, diesel and coal are fossil fuels.
In simple words: Petrol, diesel, and coal are fossil fuels because they are derived from the remains of ancient organic matter (plants and animals) buried under heat and pressure over millions of years.

🎯 Exam Tip: The key elements for defining fossil fuels are their origin from 'ancient organic matter' and formation over 'millions of years' under specific geological conditions.

Question 5.d. Uses of various allotropes of carbon.

Answer: (The answer content was not provided in the original text for this specific sub-question.)
In simple words: The various allotropes of carbon like diamond, graphite, and fullerenes have diverse applications based on their unique physical properties, for example, diamond for cutting, graphite for lubricants, and fullerenes in nanotechnology.

🎯 Exam Tip: When asked about allotropes, ensure you know at least one primary use for each (e.g., diamond's hardness for cutting, graphite's lubricity for pencils and lubricants).

Question 5.e. Use of CO2 in fire extinguisher.

Answer:

• CO\(_{2}\) based fire extinguishers do not cause corrosion and are non-conductors of electricity.
• It is beyond their capacity to extinguish a big fire.
• Therefore these fire extinguishers are used to extinguish small scale fire of electrical and electronic equipments.

In simple words: Carbon dioxide fire extinguishers are used for small electrical or electronic fires because CO2 is non-corrosive, non-conductive, and displaces oxygen, suffocating the flames.

🎯 Exam Tip: Remember CO2's non-conductive property and its ability to cut off oxygen supply are crucial for electrical fire safety.

Question 5.f. Practical uses of CO2.

Answer:Practical uses of CO\(_{2}\) are:

• CO\(_{2}\) is used to make aerated drinks.
• CO\(_{2}\) obtained by chemical reaction or kept under pressure is used in fire extinguishers. Liquified CO\(_{2}\) is used to remove caffeine from coffee.
• Liquid CO\(_{2}\) is used as solvent in modern eco-friendly dry cleaning.
• Solid carbon dioxide is used in cold storage and to keep milk and milk products and frozen substances cool during transport. It is also used for getting special effects of a mist in dramas and movies.

In simple words: Carbon dioxide has several practical applications, including carbonating aerated drinks, acting as a fire extinguisher, being a solvent for dry cleaning, and as dry ice for refrigeration and special effects.

🎯 Exam Tip: List a variety of uses, from common daily applications (drinks, dry ice) to industrial ones (fire extinguishers, solvents), to demonstrate broad understanding.

Question 6. Write two physical properties each.

Question 6.a. Diamond

Answer:Properties of diamond are:

• Brilliant and pure diamond is the hardest natural substance.
• The density of diamond is 3.5 g/cm³.
• The melting point of diamond is 3500 °C.
• When a diamond is heated at 800 °C in the presence of oxygen, CO\(_{2}\) is given away. In this process no other product besides CO\(_{2}\) is formed.
• Diamond does not dissolve in any solvent.
• Acids/bases have no effect on diamond.
• Diamond is a bad conductor of electricity as it does not have free electrons.

In simple words: Diamond is known for its extreme hardness and high melting point, and it does not conduct electricity because it lacks free electrons.

🎯 Exam Tip: Focus on hardness and non-conductivity as key properties; mentioning its high melting point and insolubility reinforces its stability.

Question 6.b. Charcoal

Answer:

• The charcoal that is made from animals is made from their bones, horns, etc.
• On the other hand, the charcoal made from plants is formed by combustion of wood in an insufficient supply of air.

In simple words: Charcoal is an amorphous form of carbon, produced by heating animal matter or wood in the absence of sufficient oxygen.

🎯 Exam Tip: Highlight charcoal's origin from incomplete combustion of organic materials as a key property.

Question 6.c. Fullerene

Answer:Properties of fullerenes are:

• Molecules of fullerenes are found in the form of buckyballs and buckytubes.
• There are 30 to 900 carbon atoms in one molecule of a fullerene.
• Fullerenes are soluble in organic solvents such as carbon disulphide, chlorobenzene.

In simple words: Fullerenes are carbon allotropes existing as buckyballs or buckytubes, containing 30 to 900 carbon atoms per molecule, and are soluble in certain organic solvents.

🎯 Exam Tip: Key properties to remember are their unique cage-like or tubular structure and solubility in organic solvents.

Question 7. Complete the following Chemical reactions.

Answer:
(a) \[\text{CH}_4 + 2\text{O}_2 \xrightarrow{\text{light}} \text{CO}_2 + 2\text{H}_2\text{O} + \text{Heat}\]
(b) \[\text{CH}_4 + \text{Cl}_2 \rightarrow \text{CHCl}_3 + \text{HCl}\] (Assuming a typo for CH\(_{4}\) + 2Cl\(_{2}\) → CH\(_{2}\)Cl\(_{2}\) + 2HCl, or CH\(_{4}\) + 3Cl\(_{2}\) → CHCl\(_{3}\) + 3HCl. Sticking verbatim to `CHCl` in OCR)
(c) \[\text{2NaOH} + \text{CO}_2 \rightarrow \text{Na}_2\text{CO}_3 + \text{H}_2\text{O}\]
(d) \[\text{2NaHCO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O} + 2\text{CO}_2\uparrow\]
(e) \[\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2\uparrow\]
In simple words: These chemical reactions demonstrate various transformations of carbon compounds, including combustion, substitution, acid-base neutralization, and decomposition, resulting in new products.

🎯 Exam Tip: For chemical reactions, ensure correct balancing of atoms on both sides and proper representation of conditions and states (e.g., heat, light, gas evolution).

Question 8. Write answers to the following in detail.

Question 8.a. What are the different types of coal? What are their uses?

Answer:Coal is a fossil fuel. It contains carbon, hydrogen and oxygen. It also contains nitrogen, phosphorus and sulphur. It occurs in the solid state. It is of four types.

• Peat: Formation of peat is the first step in the formation of coal. It contains a high proportion of water and less than 60% of carbon. Therefore, not much heat can be obtained from peat.
• Lignite: Peat was transformed into Lignite due to increased pressure and temperature inside the earth. It contains 60 to 70% of carbon.- Lignite is the second step of the formation of coal.
• Bituminous coal: Bituminous coal was formed as the third step of formation of coal. It contains 70 to 90% of carbon.
• Anthracite: Anthracite is known as the pure form of coal. This coal is hard and contains about 95% of carbon.

Uses of coal:

• Coal is used as fuel in factories and homes.
• Coal is used to obtain coke, coal gas and coal tar.
• Coal is used in thermal power plants for generation of electricity.

In simple words: Coal comes in four types - Peat, Lignite, Bituminous, and Anthracite - each differing in carbon content and heat value, and is primarily used as a fuel for power generation, industrial processes, and domestic heating.

🎯 Exam Tip: When discussing types of coal, remember the increasing order of carbon content and heat value (Peat < Lignite < Bituminous < Anthracite). For uses, categorize them broadly into fuel and industrial raw material.

Question 8.b. How will you prove experimentally that graphite is good conductor of electricity?

Answer:Apparatus required: Lead pendi, electrical wires, battery/cell, small bulb, etc.
Step-l: Remove the lead from a pencil and assemble the apparatus as shown in the diagram.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह एक साधारण विद्युत परिपथ को दर्शाता है जिसमें पेंसिल का लेड (ग्रेफाइट) एक चालक के रूप में इस्तेमाल किया गया है। इसमें एक बैटरी या सेल, बल्ब और तार जुड़े हुए हैं, जहाँ पेंसिल का लेड परिपथ को पूरा करता है, जिससे बल्ब जलता हुआ दिखाई देता है।
Step-II:

• Start the electric current in the circuit, the moment the electric current is passed through the circuit, the bulb glows.
• This experiment proves that graphite is a good conductor of electricity as graphite has free electrons moving continuously within the entire layer and these free electrons conduct electricity in the lead of the pencil.

In simple words: An experiment connecting a pencil lead (graphite) into an electrical circuit with a battery and bulb shows that the bulb glows, proving that graphite is a good conductor of electricity due to its free electrons.

🎯 Exam Tip: When describing an experiment, clearly list the apparatus, procedure steps, and the observation, linking it directly to the scientific reason (free electrons for conductivity).

Question 8.c. Explain the properties of carbon.

Answer:Allotropic nature of Carbon: Some elements occur in nature in more than one form. The chemical properties of these different forms are the same but their physical properties are different. This property of elements is called allotropy. Carbon shows the property of allotropy.
Carbon allotropes are of two types:
(A) Crystalline forms:
Carbon has three crystalline allotropes: Diamond, Graphite and Fullerene.
Properties of crystalline forms of carbon are as follows:

• A crystalline form has a regular and definite arrangement of atoms.
• They are made up of only carbon atoms.
• They have high melting points and boiling points.
• A crystalline form has a definite geometrical shape, sharp edges and plane surfaces.

(B) Amorphous forms or non-crystalline forms: Coal, charcoal, coke are the non-crystalline forms of carbon.
Properties of non-crystalline forms of carbon are as follows:

• The arrangement of carbon atoms in this form is not regular.
• Apart from carbon atoms, they also contain hydrogen, oxygen, nitrogen, phosphorus and sulfur atoms.
• Compared to a crystalline form, they have low melting and boiling points.
• Most of them are used as fuels.

In simple words: Carbon exhibits allotropy, existing in multiple forms like crystalline (diamond, graphite, fullerenes with regular atomic arrangements) and non-crystalline (coal, charcoal, coke with irregular arrangements), all having the same chemical properties but different physical ones.

🎯 Exam Tip: Define allotropy clearly and then provide examples for both crystalline and non-crystalline forms, briefly outlining their distinguishing features.

Question 8.d. Classify carbon.

Answer:Carbon is classified as follows:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र कार्बन के विभिन्न अपररूपों का वर्गीकरण दर्शाता है। कार्बन को मुख्य रूप से क्रिस्टलीय रूपों (जैसे हीरा, ग्रेफाइट, फुलरीन) और गैर-क्रिस्टलीय/अनाकार रूपों (जैसे कोयला, चारकोल, कोक) में वर्गीकृत किया गया है। गैर-क्रिस्टलीय रूपों को आगे पीट, लिग्नाइट, बिटुमिनस और एन्थ्रेसाइट में विभाजित किया गया है।
In simple words: Carbon is classified into two main types: crystalline forms (like diamond, graphite, and fullerene) and non-crystalline or amorphous forms (like coal, charcoal, and coke), which further include peat, lignite, bituminous, and anthracite.

🎯 Exam Tip: When classifying carbon, remember the two main categories (crystalline and non-crystalline) and provide specific examples for each, especially the common allotropes and coal types.

Question 9. How will you verify the properties of carbon dioxide?

Answer:Properties of carbon dioxide can be verified in the following ways:

• When a burning candle is placed in a gas jar of carbon dioxide, it extinguishes indicating that carbon dioxide is a non-combustible gas and does not support combustion.
• When carbon dioxide gas is passed through lime water, it turns lime water milky due to the formation of insoluble calcium carbonate.
• Moist blue litmus turns red in a gas jar of carbon dioxide indicating, it is acidic in nature.
• Carbon dioxide is fairly soluble in water, it dissolves in water forming carbonic acid.

In simple words: Carbon dioxide's properties can be verified by observing that it extinguishes a flame (non-combustible), turns limewater milky (forms calcium carbonate), and turns moist blue litmus red (acidic).

🎯 Exam Tip: Focus on experiments that demonstrate CO2's key properties: its non-combustible nature, its reaction with limewater, and its acidic behavior.

Class 9 Science Chapter 13 Carbon: An Important Element Intext Questions and Answers

Can you recall?

Question 1. Whatremains behind on complete combustion of any organic compound?

Answer:A black colour substance 'Carbon' remains behind on complete combustion of any organic compound.
In simple words: When any organic compound burns completely, a black residue of elemental carbon is left behind.

🎯 Exam Tip: This question tests basic observation and understanding that carbon is a fundamental component of organic matter.

Question 2. What type of element is carbon? Give some information about it.

Answer:

• Carbon is a non-metallic element. It is available ' abundantly in the nature and occurs in free as well as combined state.
• Carbon in free state is found as diamond and graphite and in combined state it is present to the extent of approximately 0.27% in the form of carbonate, coal, petroleum.
• In atmosphere, the proportion of carbon in the form of carbon dioxide is approximately 0.03%.

In simple words: Carbon is a non-metallic element found abundantly in both free forms (like diamond and graphite) and combined forms (like carbonates, coal, petroleum, and carbon dioxide in the atmosphere).

🎯 Exam Tip: Remember to classify carbon as a non-metal and provide examples of its occurrence in both free (allotropes) and combined states.

Question 3. What is an element? What are the different types of elements.

Answer:

• A substance which cannot be decomposed into simple substances by any physical or simple chemical method is called as an Element.
• An element is composed of atoms of only one kind.
• The different types of elements are:
  (a) Metals - Examples: Gold, Silver, etc.
  (b) Non-metals - Examples: Carbon, Sulphur, etc.
  (c) Metalloids - Examples: Silicon, Antimony, etc.

In simple words: An element is a pure substance made of only one type of atom that cannot be broken down further by chemical means, and elements are broadly classified as metals, non-metals, or metalloids.

🎯 Exam Tip: A clear definition of an element and examples for each of the three main categories (metals, non-metals, metalloids) are essential for a complete answer.

Answer the following questions:

Question 1. Does an electric charge form on atoms when a covalent bond is formed between them? Why is a single bond between two carbon atoms strong and stable?

Answer:

• No, electric charge is not formed on atoms when a covalent bond is formed between them. This is because covalent bond is formed by sharing of electrons.
• Therefore, there is no change in number of electrons and protons in these atoms and they remain electrically neutral.
• Covalent bonds occur when electrons are shared between two atoms. A single covalent bond is formed when only one pair of electrons is shared between atoms.
• In this sharing, the atomic orbitals directly overlap between the nuclei of two atoms forming the strongest type of covalent bond called as sigma bond.
• Hence, a single bond between two carbon atoms is strong and stable.

In simple words: No electric charge forms during covalent bonding because electrons are shared, not transferred, maintaining atomic neutrality; a single carbon-carbon bond is strong and stable due to the direct overlap of atomic orbitals forming a sigma bond.

🎯 Exam Tip: Emphasize electron sharing for neutrality and the strong, direct orbital overlap (sigma bond) for the stability of C-C single bonds.

Question 2. In which of the solvents - water, kerosene and cooking oil does the coal powder dissolve?

Answer:Solvents such as water, kerosene and cooking oil do not dissolve coal powder in them.
In simple words: Coal powder does not dissolve in common solvents like water, kerosene, or cooking oil.

🎯 Exam Tip: Recognize that coal, being largely insoluble in common liquids, behaves differently from substances that form solutions easily.

Class 9 Science Chapter 13 Carbon: An Important Element Additional Important Questions And Answers

Choose And Write The Correct Option:

Question 1.The organic compound having double or triple bond in them is termed as (a) unsaturated (b) inorganic (c) saturated (d) complete
Answer: (a) Unsaturated hydrocarbon
In simple words: Unsaturated hydrocarbons are organic compounds characterized by the presence of at least one double or triple bond between carbon atoms.

🎯 Exam Tip: Recognizing the type of bond (single, double, triple) is fundamental for classifying hydrocarbons as saturated or unsaturated, a common concept in organic chemistry. Different bond types dictate reactivity.

 

Question 2.Covalent compounds are generally soluble in solvents. (a) inorganic (b) organic (c) mixed (d) mineral
Answer: (b) organic
In simple words: Covalent compounds, especially organic ones, typically dissolve well in organic solvents due to similar intermolecular forces.

🎯 Exam Tip: The principle "like dissolves like" is crucial here. Covalent compounds, often nonpolar, are soluble in nonpolar organic solvents, unlike polar inorganic compounds that dissolve in polar solvents like water.

 

Question 3.Methane is also called as (a) maha gas (b) mar’s gas (c) Anthracite (d) marsh gas
Answer: (d) Marsh gas
In simple words: Methane is commonly known as marsh gas because it is naturally produced from the anaerobic decomposition of organic matter in wetlands or marshy areas.

🎯 Exam Tip: Knowing common names for important chemical compounds helps in understanding their natural occurrences and historical context, often tested in basic chemistry. Marsh gas is a widely recognized alternative name for methane.

 

Question 4.is an allotrope of carbon used to make ornaments.
Answer: Diamond
In simple words: Diamond, a crystalline allotrope of carbon, is highly valued and used in ornaments due to its exceptional hardness, brilliance, and aesthetic appeal.

🎯 Exam Tip: Allotropes of carbon have distinct physical properties despite identical chemical composition. Understanding these differences, like diamond's hardness versus graphite's softness, is key for applications and is a frequent exam question.

 

Question 5.The number of valence electrons in carbon is (a) 4 (b) 5 (c) 6 (d) 3
Answer: (a) 4
In simple words: Carbon has an atomic number of 6, and its electron configuration \(2, 4\) means it has four electrons in its outermost shell, which are its valence electrons.

🎯 Exam Tip: The number of valence electrons determines an element's bonding behavior. Carbon's tetravalency (4 valence electrons) is crucial for forming diverse organic compounds, a core concept in carbon chemistry.

 

Question 6.In saturated hydrocarbons, two carbon atoms are linked by (a) double bond (b) triple bond (c) multiple bond (d) single bond
Answer: (d) single bond
In simple words: Saturated hydrocarbons are defined by having only single covalent bonds between their carbon atoms, allowing for maximum hydrogen saturation.

🎯 Exam Tip: Differentiating between saturated (single bonds only) and unsaturated (double or triple bonds present) hydrocarbons is a fundamental classification in organic chemistry, essential for understanding their structure and reactivity.

 

Question 7.Carbon has 4 valence electrons in its outermost shell, hence, it is (a) divalent (b) tetravalent (c) trivalent (d) pentavalent
Answer: (b) tetravalent
In simple words: An element is tetravalent if it has four valence electrons, allowing it to form four covalent bonds, as is the case with carbon.

🎯 Exam Tip: The valency of an element dictates the number of bonds it can form. Carbon's tetravalency is the basis of its ability to form long chains and complex structures, which is key to organic chemistry.

 

Question 8.Methanogenic bacteria act on the organic acids to produce (a) oxygen gas (b) nitrogen gas (c) methane gas (d) carbon dioxide gas
Answer: (c) Methane gas
In simple words: Methanogenic bacteria are microorganisms that produce methane as a metabolic byproduct by breaking down organic acids and other organic compounds in anaerobic conditions.

🎯 Exam Tip: Understanding the role of specific bacteria in biochemical processes, such as methanogenesis, highlights the interdisciplinary nature of science, connecting biology with environmental chemistry, and is often tested in topics related to biogas production.

 

Question 9.is used to remove caffeine from coffee. (a) liquefied O2 (b) liquefied N2 (c) liquefied CO2 (d) liquefied CH4
Answer: (c) Liquified CO2
In simple words: Liquefied carbon dioxide is used in a process called supercritical fluid extraction to effectively remove caffeine from coffee beans without the need for harsh chemical solvents.

🎯 Exam Tip: Real-world applications of chemical compounds, such as liquid CO2 in decaffeination, demonstrate practical knowledge and often appear in applied chemistry questions.

 

Question 10.Exhaled air contains about CO2. (a) 4% (b) 3% (c) 5% (d) 6%
Answer: (a) 4%
In simple words: When humans exhale, the air released contains roughly 4% carbon dioxide, which is a byproduct of cellular respiration.

🎯 Exam Tip: Knowing the approximate composition of inhaled and exhaled air is a basic fact in human physiology and respiratory science, frequently asked in general science exams.

 

Question 11.Electronic configuration of carbon is (a) (2, 2) (b) (2,4) (c) (2, 5,4) (d) (2, 6)
Answer: (b) 2, 4
In simple words: Carbon, with an atomic number of 6, has its electrons arranged in two shells: two in the first shell and four in the second (outermost) shell.

🎯 Exam Tip: Electronic configuration is fundamental to understanding an element's chemical properties and reactivity. For carbon, its \(2, 4\) configuration explains its tetravalency and ability to form covalent bonds.

 

Question 12.Molecular formula of ethane is (a) C3H4 (b) C2H4 (c) C2H6 (d) C2H2
Answer: (c) C2H6
In simple words: Ethane is a simple alkane consisting of two carbon atoms connected by a single bond, with six hydrogen atoms completing its structure.

🎯 Exam Tip: Familiarity with the molecular formulas of common hydrocarbons (alkanes, alkenes, alkynes) is essential for basic organic chemistry and often tested in naming and structural questions.

 

Question 13.Molecular mass of carbon dioxide is (a) 28 (b) 22 (c) 56 (d) 44
Answer: (d) 44
In simple words: The molecular mass of carbon dioxide (\(CO_2\)) is calculated by adding the atomic mass of one carbon atom (approximately 12 amu) and two oxygen atoms (approximately 16 amu each), resulting in \(12 + 2 \times 16 = 44\) amu.

🎯 Exam Tip: Calculating molecular mass accurately is a basic skill in chemistry, requiring knowledge of atomic masses of common elements and correct interpretation of chemical formulas.

 

Question 14.On heating a mixture of hydrogen and carbon monoxide gases at 300°C in the presence of nickel (catalyst) is formed. (a) carbon dioxide gas (b) oxygen gas (c) methane gas (d) ethylene gas
Answer: (c) methane gas
In simple words: The reaction of hydrogen and carbon monoxide in the presence of a nickel catalyst at elevated temperatures (Fischer-Tropsch synthesis variant) primarily produces methane and water.

🎯 Exam Tip: Understanding common industrial reactions and the role of catalysts, like nickel in methane synthesis from syngas (CO and H2), is important for applied chemistry and chemical processes.

 

Question 15.Ethane with molecular formula C2H6 has covalent bonds. (a) six (b) seven (c) eight (d) nine
Answer: (b) seven
In simple words: In ethane (\(C_2H_6\)), there is one carbon-carbon single bond and six carbon-hydrogen single bonds, totaling seven covalent bonds.

🎯 Exam Tip: Being able to visualize or draw the structural formula of simple organic molecules helps in correctly counting the number of covalent bonds, a key skill for understanding molecular structure.

 

Question 15.Weight of Kohinoor Diamond was (a) 186 carats (b) 27 carats (c) 252 carats (d) 23 carats
Answer: (a) 186 carats
In simple words: The Kohinoor diamond, one of the most famous diamonds in the world, initially weighed 186 carats before it was recut.

🎯 Exam Tip: While specific historical facts like the weight of famous diamonds might not be core chemistry, they can be included as general knowledge or interesting facts related to a chapter on carbon allotropes. Students should be aware of such tangential information.

 

Question 16.Covalent compounds have (a) high melting point (b) low melting point (c) moderate melting point (d) very high melting point
Answer: (b) low melting point
In simple words: Covalent compounds generally have low melting points because the intermolecular forces holding the molecules together are relatively weak, requiring less energy to overcome.

🎯 Exam Tip: The nature of bonding (covalent vs. ionic) significantly impacts physical properties like melting and boiling points. Covalent compounds typically exhibit lower melting points due to weaker intermolecular forces compared to the strong electrostatic forces in ionic compounds.

 

Question 17.Methane is (a) C2H6 (b) C3H8 (C) CH2 (d) CH4
Answer: (d) CH4
In simple words: Methane is the simplest hydrocarbon, consisting of one carbon atom bonded to four hydrogen atoms.

🎯 Exam Tip: Memorizing the molecular formulas of basic organic compounds like methane, ethane, and propane is fundamental for organic chemistry and forms the basis for understanding homologous series.

 

Question 18.Wohler, a German scientist synthesized the compound from an inorganic compound ammonium cyanate. (a) methane (b) ethylene (c) urea (d) acetic acid
Answer: (c) urea
In simple words: In 1828, Friedrich Wohler synthesized urea from ammonium cyanate, marking a significant milestone as the first synthesis of an organic compound from an inorganic precursor.

🎯 Exam Tip: Wohler's synthesis of urea is a landmark experiment in chemistry, disproving the vital force theory and establishing the field of organic chemistry. This historical context is often important for understanding the evolution of scientific thought.

 

Question 19.Molecular mass of methane is (a) 19 (b) 16 (c) 17 (d) 18
Answer: (b) 16
In simple words: The molecular mass of methane (\(CH_4\)) is calculated by adding the atomic mass of one carbon atom (12 amu) and four hydrogen atoms (1 amu each), resulting in \(12 + 4 \times 1 = 16\) amu.

🎯 Exam Tip: Accurate calculation of molecular mass is a fundamental skill. For simple molecules like methane, it's a straightforward sum of atomic masses, frequently tested in stoichiometry and basic chemistry problems.

 

Question 20.coal contains highest percentage of carbon. (a) Bituminous (b) Peat (c) Anthracite (d) Lignite
Answer: (c) Anthracite
In simple words: Anthracite is the highest rank of coal, known for its very hard, brittle, and lustrous nature, and containing the highest carbon content among all types of coal.

🎯 Exam Tip: Understanding the different types of coal and their carbon content is crucial for energy resources and environmental science. Anthracite, with its high carbon percentage, is often associated with higher energy output and cleaner burning.

 

Question 21.H2C = CH2 is (a) Propane (b) Ethyne (c) Ethane (d) Ethene
Answer: (d) Ethene
In simple words: H2C=CH2 represents ethene, an alkene with a double bond between two carbon atoms, which is also commonly known as ethylene.

🎯 Exam Tip: Recognizing molecular formulas and structures to correctly name hydrocarbons (alkanes, alkenes, alkynes) is a foundational skill in organic chemistry and is frequently assessed.

 

Question 22.CH3- C = CH is (a) Propene (b) Propyne (c) Ethyne (d) Ethene
Answer: (b) Propyne
In simple words: CH3-C≡CH is the structural formula for propyne, an alkyne with a triple bond between two carbon atoms and a methyl group attached.

🎯 Exam Tip: Being able to identify the correct systematic name from a given structural formula, especially for compounds containing double or triple bonds, is a fundamental IUPAC nomenclature skill in organic chemistry.

 

Question 23.Carbon dioxide gas is not used in (a) photosynthesis (b) aerated drinks (c) glass cutting (d) fire extinguishers
Answer: (c) glass cutting
In simple words: Carbon dioxide is not used for cutting glass; glass cutting typically involves tools like diamond cutters or specialized lasers.

🎯 Exam Tip: Knowing the common applications and non-applications of key chemical compounds helps distinguish between their various industrial and biological roles, often tested in multiple-choice questions.

 

Question 24.Melting point of diamond is (a) 3700 °C (b) 3500 °C (c) 4000 °C (d) 2500 °C
Answer: (b) 3500 °C
In simple words: Diamond has an extremely high melting point, approximately 3500 °C, due to its strong covalent network structure.

🎯 Exam Tip: Extreme physical properties like very high melting points for substances like diamond are direct consequences of their strong atomic bonding and crystal structure, an important concept in materials science.

 

Question 25.Melting point of CO2 is (a) 26 °C (b) 56 °C (c) -56.6°C (d) -98°C
Answer: (c) -56.6 °C
In simple words: Carbon dioxide solidifies and sublimes directly from solid to gas at -56.6 °C, as it does not typically melt into a liquid at atmospheric pressure.

🎯 Exam Tip: Understanding phase transitions and specific melting/sublimation points for common substances like CO2 (dry ice) is important for practical applications and distinguishing properties under different conditions.

 

Question 26.Melting point of methane is (a) -182.5 °C (b) -161.5 °C (c) 182.5 °C (d) 161.5 °C
Answer: (a) -182.5 °C
In simple words: Methane has a very low melting point of -182.5 °C, characteristic of a small, nonpolar molecule with weak intermolecular forces.

🎯 Exam Tip: Low melting and boiling points for simple molecular compounds like methane are explained by weak intermolecular forces, a key concept when comparing physical properties of different types of compounds.

 

Question 27.Biogas contains about methane. (a) 55% to 60% (b) 20% to 25% (c) 90% to 95% (d) 40% to 45%
Answer: (a) 55% to 60%
In simple words: Biogas, a renewable energy source, is primarily composed of methane, typically ranging from 55% to 60%, along with carbon dioxide and other trace gases.

🎯 Exam Tip: Knowing the approximate composition of important fuels like biogas is relevant for understanding their energy potential and environmental implications, often covered in topics on sustainable energy.

 

Question 28.is not a property of carbon dioxide gas. (a) Supporting combustion (b) Odourless (c) Colourless (d) Turns blue litmus red
Answer: (a) Supporting combustion
In simple words: Carbon dioxide is well-known for being a non-combustible gas that does not support combustion, which is why it is used in fire extinguishers.

🎯 Exam Tip: Understanding the chemical behavior of common gases, such as CO2's role in extinguishing fires, is crucial for both theoretical knowledge and practical safety applications.

Name The Following:

 

Question 1.Industries that use methane in the form of natural gas.
Answer: Fabric mills, paper mills, food processing industry, petrol purification.
In simple words: Methane, as natural gas, is a versatile fuel used in various industries including textiles, paper manufacturing, food processing, and petroleum refining.

🎯 Exam Tip: Recognizing the industrial applications of common gases like methane highlights the practical relevance of chemistry and its impact on various sectors.

 

Question 2.Organic compounds prepared from methane.
Answer: Ethanol, methyl chloride, methylene chloride, acetylene.
In simple words: Methane can serve as a precursor for synthesizing various organic compounds such as alcohols, chlorinated methane derivatives, and alkynes.

🎯 Exam Tip: Knowing the synthesis pathways from simple hydrocarbons like methane to more complex organic compounds is fundamental to understanding organic reactions and industrial synthesis.

 

Question 3.Chemicals used in regular fire extinguisher.
Answer: Sodium bicarbonate and dilute sulphuric acid.
In simple words: Traditional fire extinguishers utilize the reaction between sodium bicarbonate and dilute sulphuric acid to produce carbon dioxide, which smothers fires.

🎯 Exam Tip: Understanding the chemical reactions behind common safety equipment, like fire extinguishers, provides practical knowledge about acid-base reactions and gas production.

 

Question 4.Components of biogas
Answer: Methane, carbon dioxide
In simple words: Biogas is primarily composed of methane, which is the main combustible component, and carbon dioxide, which is a significant byproduct.

🎯 Exam Tip: Knowing the main constituents of biogas is important for understanding its properties as a fuel and its role in renewable energy systems.

 

Question 5.Organic solvents in which fullerenes are soluble.
Answer: Carbon disulfide, chlorobenzene.
In simple words: Fullerenes are soluble in certain organic solvents such as carbon disulfide and chlorobenzene, which allows for their purification and processing.

🎯 Exam Tip: Solubility properties are crucial for handling and isolating substances. For fullerenes, knowing appropriate solvents helps in their study and application, reflecting the "like dissolves like" principle for nonpolar substances.

 

Question 6.Use of carbon dioxide in dramas and movies
Answer: The special effect of mist.
In simple words: Solid carbon dioxide (dry ice) is used to create atmospheric fog or mist effects in theatrical productions and films when it sublimes in contact with water.

🎯 Exam Tip: Practical and creative applications of scientific principles, such as the sublimation of dry ice for special effects, illustrate the diverse uses of chemical compounds beyond typical laboratory settings.

Match The Columns:

 

Question 1.

Column 'A'	Column 'B'
(1) Diamond	(a) Hexagonal layered structure
(2) Fullerenes	(b) Tetragonal three-dimensional structure
(3) Graphite	(c) Geodesic dome

Answer:(1-b), (2- c), (3 - a)
In simple words: Diamond has a tetragonal structure, fullerenes are characterized by a geodesic dome shape, and graphite consists of hexagonal layered structures.

🎯 Exam Tip: Matching allotropes of carbon with their distinctive crystal or molecular structures is a key test of understanding the relationship between structure and properties in materials science.

 

Question 2.

Column 'A'	Column 'B'
(1) Peat	(a) 60-70% of Carbon
(2) Lignite	(b) 95% of Carbon
(3) Bituminous	(c) less than 60% of Carbon
(4) Anthracite	(d) 70 – 90% of Carbon

Answer:(1 – с), (2 – а), (3 – d), (4 - b)
In simple words: Different types of coal—peat, lignite, bituminous, and anthracite—are categorized by their increasing carbon content, reflecting stages of coal formation.

🎯 Exam Tip: Knowledge of the carbon content in different types of coal helps in understanding their energy value and geological formation, a common topic in geology and energy resources.

 

Question 3.

Column 'A'	Column 'B'
(1) Propyne	(a) CH3-CH2-CH3
(2) Propene	(b) CH3 – C = CH
(3) Propane	(c) CH3 – CH = CH2

Answer:(1 – b), (2 - с), (3 – a)
In simple words: Propyne is an alkyne with a triple bond, propene is an alkene with a double bond, and propane is an alkane with only single bonds, all containing three carbon atoms.

🎯 Exam Tip: Correctly matching the names of simple hydrocarbons (alkanes, alkenes, alkynes) with their corresponding structural formulas is fundamental for understanding organic nomenclature and isomerism.

 

Question 4.

Column 'A'	Column 'B'
(1) Fullerene	(a) Lubricants
(2) Diamond	(b) Insulator
(3) Graphite	(c) Ornaments

Answer:(1 – b), (2 – с), (3 – a)
In simple words: Fullerenes can act as insulators, diamonds are used for ornaments, and graphite is utilized as a lubricant due to their unique properties.

🎯 Exam Tip: Understanding the specific applications of different carbon allotropes based on their physical properties (e.g., conductivity, hardness, slipperiness) is important for relating structure to function.

 

Question 5.

Column 'A	Column 'B'
(1) Water gas	(a) CH4
(2) Methane gas	(b) CO + H2
(3) Producer gas	(c) CO2
(4) Carbon dioxide gas	(d) CO + H2 + CO2 + N2

Answer:(1 – b), (2 – a), (3 – d), (4 - c)
In simple words: Water gas is a mixture of carbon monoxide and hydrogen, methane gas is \(CH_4\), producer gas is a mix of CO, H2, CO2, and N2, and carbon dioxide gas is \(CO_2\).

🎯 Exam Tip: Knowing the chemical composition of various industrial gases and common chemical compounds is essential for understanding their production, uses, and related chemical reactions.

 

State Whether The Following Statements Are True Or False. Correct The False Statement.

 

Question 1.(1) Study of organic compounds is called as organic chemistry.
Answer: (1) True
In simple words: Organic chemistry is a specialized branch of chemistry focused on the study of carbon-containing compounds.

🎯 Exam Tip: Defining branches of chemistry helps establish foundational knowledge. Organic chemistry is a vast field centered on carbon's unique bonding capabilities.

 

(2) Hydrocarbons with double bonds are called as saturated hydrocarbons.
Answer: (2) False. Hydrocarbons with double bonds are called as Unsaturated hydrocarbons.
In simple words: Hydrocarbons with double bonds are classified as unsaturated because they contain less than the maximum possible number of hydrogen atoms.

🎯 Exam Tip: Correctly distinguishing between saturated (single bonds) and unsaturated (double/triple bonds) hydrocarbons is a fundamental classification in organic chemistry, indicating different reactivity profiles.

 

(3) Ethene is saturated hydrocarbon.
Answer: (3) False. Ethene is Unsaturated hydrocarbon.
In simple words: Ethene, having a carbon-carbon double bond, is an unsaturated hydrocarbon.

🎯 Exam Tip: Applying hydrocarbon classification to specific examples like ethene reinforces understanding of bonding and saturation, a key concept for identifying organic compounds.

 

(4) Covalent compounds are good conductor of electricity.
Answer: (4) False. Covalent compounds are bad conductor of electricity.
In simple words: Covalent compounds generally do not conduct electricity because they lack free moving ions or delocalized electrons.

🎯 Exam Tip: The electrical conductivity of compounds is directly linked to the presence of free charge carriers (ions or electrons). Covalent compounds usually don't have these, making them insulators.

 

(5) Methane is a covalent compound.
Answer: (5) True
In simple words: Methane is a covalent compound because its carbon and hydrogen atoms share electrons to form strong covalent bonds.

🎯 Exam Tip: Identifying bond types (ionic vs. covalent) for common compounds like methane is a basic chemistry skill, demonstrating an understanding of electron sharing.

 

(6) Covalent compounds are soluble in organic solvents.
Answer: (6) True
In simple words: Many covalent compounds, especially nonpolar ones, dissolve well in organic solvents due to similar intermolecular forces.

🎯 Exam Tip: The "like dissolves like" principle is crucial here. Covalent compounds (often nonpolar) are more soluble in organic (nonpolar) solvents than in polar solvents like water.

 

(7) Graphite is used in making lubricants and lead pencils.
Answer: (7) True
In simple words: Graphite's layered structure allows its layers to slide past each other, making it an excellent solid lubricant and a key component in pencil leads.

🎯 Exam Tip: Relate the unique layered structure of graphite to its practical applications (lubricant, pencil lead), which is a classic example of how atomic arrangement dictates macroscopic properties.

 

(8) The density of diamond is 9.8 g/cm³.
Answer: (8) False: The density of diamond is 3.5 g/cm³.
In simple words: Diamond has a high density of approximately 3.5 g/cm³, but not 9.8 g/cm³.

🎯 Exam Tip: Accurate recall of physical properties like density for important substances such as diamond is necessary, as incorrect values can lead to misconceptions about their nature.

 

(9) Diamond knives are used in eye surgery.
Answer: (9) True
In simple words: Diamond knives are employed in delicate eye surgeries due to their extreme sharpness and durability.

🎯 Exam Tip: Understanding specialized applications of materials like diamond in medicine highlights their unique properties and the demands of precision industries.

 

(10) Fullerenes are used as insulators.
Answer: (10) True
In simple words: Fullerenes are carbon allotropes that do not readily conduct electricity under normal conditions, making them useful as insulators.

🎯 Exam Tip: Knowing whether a material acts as a conductor or insulator is crucial for its application in electronics and electrical systems, and fullerenes demonstrate varied properties depending on their specific structure and doping.

 

(11) Coke is used in production of water gas i.e. (CO2 + H2O).
Answer: (11) False. Coke is used in production of water gas i.e. (CO + H2).
In simple words: Coke reacts with steam to produce water gas, which is a mixture of carbon monoxide and hydrogen, not carbon dioxide and water.

🎯 Exam Tip: Accurately recalling chemical formulas and reaction products, such as the components of water gas, is essential for understanding industrial processes and preventing common errors.

 

(12) Structural formula of propyne is CH3 – C = CH.
Answer: (12) False. Structural formula of propyne is CH3 – C ≡ CH.
In simple words: Propyne, being an alkyne, must contain a carbon-carbon triple bond, indicated by C≡CH, not a double bond.

🎯 Exam Tip: Precision in structural formulas, especially regarding the type and number of bonds, is critical in organic chemistry for correct identification and understanding of chemical properties.

 

(13) COz is used to make aerated drinks.
Answer: (13) True
In simple words: Carbon dioxide is dissolved under pressure in water to create aerated drinks, giving them their characteristic fizziness.

🎯 Exam Tip: Understanding the common applications of gases, such as CO2 in carbonated beverages, connects chemistry to everyday life and is a frequent general science fact.

 

(14) False. Methane gas is colourless.
Answer: (14) False. Methane gas is colourless.
In simple words: Methane is a colorless gas, meaning it does not possess any visible hue.

🎯 Exam Tip: Basic physical properties like color, odor, and state of matter are important for identifying and describing common gases, and mistakes can lead to misunderstanding their nature.

 

(15) False. Production of biogas is anaerobic process.
Answer: (15) False. Production of biogas is anaerobic process.
In simple words: Biogas is produced through anaerobic digestion, a process that occurs in the absence of oxygen.

🎯 Exam Tip: Differentiating between aerobic (with oxygen) and anaerobic (without oxygen) processes is fundamental in biology and environmental science, particularly for understanding decomposition and energy production like biogas.

Find The Odd Man Out:

 

Question 1.Propane, Methane, Ethene, Pentane.
Answer: Ethene. It is an unsaturated hydrocarbon with double bond between two carbon atoms while rest are saturated hydrocarbons with single bond between two carbon atoms.
In simple words: Ethene is the odd one out because it is an alkene with a double bond, while propane, methane, and pentane are all alkanes with only single bonds.

🎯 Exam Tip: Classifying hydrocarbons based on their bonding (saturated vs. unsaturated) is a key skill. The presence of a double bond makes ethene chemically distinct from the other alkanes listed.

 

Question 2.CH4, C2H6, C3H8, CaCO3.
Answer: CaCO3. It is a salt which is an inorganic' compound, while rest are hydrocarbon compounds, i.e. organic compounds.
In simple words: Calcium carbonate (\(CaCO_3\)) is an inorganic compound, distinguishing it from methane, ethane, and propane, which are all organic hydrocarbon compounds.

🎯 Exam Tip: The ability to differentiate between organic and inorganic compounds based on their chemical composition is a foundational concept in chemistry, often revolving around the presence of carbon-hydrogen bonds.

 

Question 3.C2H2, C3H8, C2H6, CH4.
Answer: C2H2. It is an unsaturated hydrocarbon with triple bonds while rest are saturated hydrocarbons with single bonds between two carbon atoms.
In simple words: \(C_2H_2\) (ethyne) is the odd one out because it is an alkyne with a triple bond, whereas \(C_3H_8\), \(C_2H_6\), and \(CH_4\) are alkanes with only single bonds.

🎯 Exam Tip: Identifying the degree of saturation (single, double, or triple bonds) is crucial for classifying hydrocarbons. Ethyne's triple bond makes it distinct from the saturated alkanes.

 

Question 4.Diamond, Fullerene, Graphite, Methane.
Answer: Methane. It is a marsh gas while rest are allotropes of carbon.
In simple words: Methane is a compound of carbon and hydrogen, whereas diamond, fullerene, and graphite are pure elemental forms (allotropes) of carbon.

🎯 Exam Tip: Distinguishing between elements and compounds is a fundamental concept. Allotropes are different structural forms of the same element, while methane is a molecule composed of two different elements.

 

Question 5.Coal, Petroleum, Natural gas, Cotton
Answer: Cotton. Cotton is a natural fibre while rest all are fossil fuels.
In simple words: Cotton is a natural plant fiber, distinct from coal, petroleum, and natural gas, which are all fossil fuels formed from ancient organic matter.

🎯 Exam Tip: Grouping substances based on their origin and chemical classification (e.g., fossil fuels vs. natural fibers) is important for understanding their properties and uses in various contexts.

 

Question 6.Cotton, Silk, Proteins, Wool
Answer: Proteins. Proteins are carbonaceous nutrients while rest all are natural fibres.
In simple words: Proteins are a class of carbon-containing nutrients, while cotton, silk, and wool are all natural fibers used in textiles.

🎯 Exam Tip: Differentiating between broad biological macromolecules (like proteins) and specific material classifications (like natural fibers) requires an understanding of their primary roles and structures.

 

Question 7.Carbohydrates, Coal, Proteins, Fats
Answer: Coal. Coal is a fossil fuel while rest all are carbonaceous nutrients.
In simple words: Coal is a fossil fuel, whereas carbohydrates, proteins, and fats are all organic macronutrients vital for living organisms.

🎯 Exam Tip: Grouping substances by their primary biological or geological function (e.g., nutrients vs. fossil fuels) is important for a holistic understanding of carbon-based compounds.

 

Question 8.Peat, Charcoal, Lignite, Bituminous
Answer: Charcoal. Charcoal is a non-crystalline form of carbon while rest all are types of coal.
In simple words: Charcoal is an amorphous form of carbon produced by charring wood, whereas peat, lignite, and bituminous are natural ranks of coal.

🎯 Exam Tip: Distinguishing between natural geological formations (types of coal) and manufactured carbon forms (charcoal) is crucial for understanding different carbon sources.

 

Question 9.Lubricants, Electrodes, Ornaments, Arc Lamps
Answer: Ornaments. Ornaments are made from diamonds while rest all are made from graphite.
In simple words: Ornaments are typically made from diamond, while lubricants, electrodes, and arc lamps utilize graphite.

🎯 Exam Tip: Identifying applications that specifically use diamond versus those that use graphite highlights the contrasting physical properties and uses of these two major carbon allotropes.

Write The Correlated Terms:

 

Question 1.(1) Propene : Double bond :: Propyne :
Answer: (1) Triple Bond
In simple words: Propene has a double bond, and similarly, propyne has a triple bond.

🎯 Exam Tip: Understanding the relationship between the "-ene" and "-yne" suffixes in organic nomenclature directly indicates the presence of double and triple carbon-carbon bonds, respectively.

 

(2) Ethane : CH3 – CH3 :: Ethene :
Answer: (2) CH2 = CH2
In simple words: Ethane's structural formula is CH3-CH3, so ethene's structural formula is CH2=CH2.

🎯 Exam Tip: Correlating the name of a hydrocarbon with its correct structural formula, especially noting the presence of single versus double bonds, is a basic requirement in organic chemistry.

 

(3) Hydrogen : Monovalent :: Carbon :
Answer: (3) Tetravalent
In simple words: Hydrogen is monovalent (forms one bond), and carbon is tetravalent (forms four bonds).

🎯 Exam Tip: Knowing the valency of common elements like hydrogen and carbon is fundamental to drawing correct chemical structures and understanding bonding patterns.

 

(4) Methane: Low melting point i.e. -182.5°C Diamond :
Answer: (4) High melting point i.e. 3500°C
In simple words: Methane has a low melting point, while diamond has a very high melting point.

🎯 Exam Tip: Contrasting the physical properties, such as melting points, between simple molecular substances (methane) and giant covalent structures (diamond) illustrates the effect of intermolecular versus intramolecular forces.

 

(5) Graphite: Hexagonal structure :: Diamond :
Answer: (5) Tetragonal structure
In simple words: Graphite has a hexagonal layered structure, and diamond has a tetragonal three-dimensional structure.

🎯 Exam Tip: Relating the macroscopic properties of carbon allotropes to their microscopic crystal structures (hexagonal for graphite, tetragonal for diamond) is crucial for understanding their diverse applications.

 

(6) Density of Diamond : 3.5 g/cm³ :: Density of Graphite :
Answer: (6) 1.9 to 2.3 g/cm³
In simple words: The density of diamond is 3.5 g/cm³, while the density of graphite ranges from 1.9 to 2.3 g/cm³.

🎯 Exam Tip: Comparing the densities of carbon allotropes (diamond vs. graphite) highlights how different atomic arrangements of the same element can lead to distinct physical properties.

 

(7) Peat: 60% of carbon :: Anthracite :
Answer: (7) 95% of carbon
In simple words: Peat contains less than 60% carbon, and anthracite contains about 95% carbon.

🎯 Exam Tip: Knowing the typical carbon content for different ranks of coal (peat as low, anthracite as high) is important for understanding their energy quality and geological classification.

 

(8) Melting point of CO2: -56.6°C :: Melting point of CH4:
Answer: (8) -182.5 °C
In simple words: Carbon dioxide has a melting point of -56.6°C, and methane has a melting point of -182.5°C.

🎯 Exam Tip: Accurate recall of specific physical constants like melting points for common gases is important for comparison and understanding their behavior under different temperature conditions.

 

Question 1. Covalent compounds have low melting and boiling points.
Answer:

• When substances melt or boil, bonds between the molecules are broken due to heat supplied.
• On covalent compounds, the intermolecular forces of attraction are weak.
• Hence, intermolecular forces in covalent compounds are broken easily due to which they have low melting and boiling points.

In simple words: Covalent compounds have low melting and boiling points because the forces holding their molecules together are weak, requiring less energy to break them during melting or boiling.

🎯 Exam Tip: Understanding the nature of intermolecular forces is key to explaining the physical properties of compounds like melting and boiling points.

 

Question 2. Graphite is a good conductor of electricity whereas diamond is a non-conductor of electricity.
Answer:

• In diamond, each carbon atom uses all its four electronic to get bonded to another carbon atom, whereas in graphite each carbon uses there out of four electrons during bonding.
• Hence in diamond no free electrons are left whereas in graphite free electrons are available.
• Due to the presence of electron which are free to flow graphite is a good conductor of electricity, whereas due to the absence of free electrons diamond is a non-conductor of electricity.

In simple words: Graphite conducts electricity because it has free electrons that can move, while diamond does not because all its electrons are used in strong bonds, leaving no free electrons for conduction.

🎯 Exam Tip: The bonding structure and availability of free electrons determine an allotrope's electrical conductivity. Focus on the number of bonds each carbon atom forms.

 

Question 3. Graphite is used as a lubricant.
Answer:

• Lubricants are used to reduce friction and wear and tear of mechanical parts.
• Graphite is smooth and slippery and hence is useful in reducing friction. Hence, graphite is used as a lubricant.

In simple words: Graphite's layered structure allows its layers to slide easily over each other, making it smooth and slippery, which is why it's used to reduce friction as a lubricant.

🎯 Exam Tip: The unique hexagonal layered structure of graphite directly contributes to its lubricating properties, a common application-based question.

 

Question 4. Methane is used as a domestic fuel.
Answer:

• Methane is highly inflammable.
• It burns by reacting with oxygen to give a bluish flame.
• It burns completely and producers 213 Kcal/ mol of heat.
• Being the smallest hydrocarbon, the proportion of CO2 released in the combustion of methane is small.
• Therefore methane is used as a domestic fuel.

In simple words: Methane is an efficient domestic fuel because it is highly flammable, burns completely with a clean flame, releases a significant amount of heat, and produces minimal carbon dioxide.

🎯 Exam Tip: When discussing fuels, emphasize flammability, heat output, and environmental impact (CO2 release) as key factors for their use.

 

Question 1. What was the contribution of chemist Wohier in organic chemistry?
Answer:

• The German chemist Wohler synthesized an organic compound urea from an inorganic compound ammonium cyanate,
• Ever since then, many organic compounds have been made from inorganic compounds.
• Carbon was found to he the main element in all these compounds.
• Hence, organic chemistry is also referred to as chem is try of carbon corn pounds.

In simple words: Chemist Wohler's major contribution was synthesizing urea (an organic compound) from ammonium cyanate (an inorganic compound), which disproved the vital force theory and paved the way for the development of organic chemistry, emphasizing carbon as its core element.

🎯 Exam Tip: Wohler's synthesis of urea is a landmark event in chemistry, signifying the birth of modern organic chemistry and the ability to create organic compounds from inorganic precursors.

 

Question 2. With neat diagram explain the structure of diamond.
Ans.

• In diamond, every carbon atom is bonded to four neighbouring atoms by covalent bonds.
• Therefore, diamond has a tetragonal three dimensional structure which makes it very hard.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र हीरे में कार्बन परमाणुओं की संरचना को दर्शाता है। प्रत्येक कार्बन परमाणु चार पड़ोसी कार्बन परमाणुओं से सहसंयोजक बंधों द्वारा जुड़ा होता है, जिससे एक मजबूत चतुष्कोणीय त्रि-आयामी जाली संरचना बनती है। यह व्यवस्था हीरे को असाधारण रूप से कठोर बनाती है।In simple words: Diamond has a tetragonal three-dimensional structure where each carbon atom is strongly bonded to four other carbon atoms, creating a rigid and very hard crystal lattice.

🎯 Exam Tip: When describing diamond's structure, highlight the strong covalent bonds and the specific tetragonal arrangement, as these explain its hardness and non-conductivity.

 

Question 3. With neat diagram explain the structure of graphite?
Answer:

• Every carbon atom in graphite is bonded to three other carbon atoms in such a way that a hexagonal layered structure is formed.
• A graphite crystal is made of many sheets or layers of carbon atoms.
• These layers slip over each other on applying pressure.
• One layer of graphite is called graphene.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र ग्रेफाइट में कार्बन परमाणुओं की संरचना को दर्शाता है। प्रत्येक कार्बन परमाणु तीन अन्य कार्बन परमाणुओं से जुड़कर एक षट्कोणीय परतदार संरचना बनाता है। ये परतें एक दूसरे पर आसानी से फिसल सकती हैं, जो ग्रेफाइट को चिकना बनाती है।In simple words: Graphite has a hexagonal layered structure where each carbon atom is bonded to three others within flat layers, and these layers can easily slide over each other.

🎯 Exam Tip: Focus on the hexagonal layered structure and the weak forces between layers to explain graphite's properties like softness, slipperiness, and electrical conductivity.

 

Question 4. Give the properties of graphite.
Answer:Properties of graphite are:

• Graphite found in nature is black, soft, brittle and slippery.
• Inside each layer of graphite, free electrons move continuously within the entire layer. That is why graphite is a good conductor of electricity.
• Due to the layered structure graphite can be used for writing on paper.
• The density of graphite is 1.9 to 2.3 g/cm³.
• Graphite does not dissolve in most solvents.

In simple words: Graphite is a black, soft, and slippery solid that conducts electricity due to free electrons within its hexagonal layered structure, allowing it to be used for writing and as a lubricant.

🎯 Exam Tip: When listing properties, connect each property to a structural feature of graphite, e.g., layered structure for slipperiness and writing, free electrons for conductivity.

 

Question 5. Give the uses of graphite.
Answer:Uses of graphite are:

• Graphite is used for making lubricants.
• Graphite is used for making carbon electrodes.
• Graphite is used in pencils for writing.
• Graphite is used in paints and polish.
• Graphite is used in arc lamps which gives a very bright light.

In simple words: Graphite is used as a lubricant, in carbon electrodes, for pencils, in paints and polish, and in arc lamps due to its unique properties like slipperiness and conductivity.

🎯 Exam Tip: Listing diverse applications of graphite showcases an understanding of its versatile properties; remember common uses like pencils and lubricants.

 

Question 6. Give the uses of fullerenes.
Answer:Uses of Fullerenes are:

• Fullerenes are used as insulators.
• Fullerenes are used as a catalyst in water purification.
• At a certain temperature, fullerene exhibits superconductivity.

In simple words: Fullerenes are used as insulators, catalysts in water purification, and can exhibit superconductivity at specific temperatures.

🎯 Exam Tip: For fullerenes, remember their emerging high-tech applications rather than everyday uses, particularly their role in catalysis and superconductivity.

 

Question 7. What is Coal?
Answer:

• Coal is a fossil fuel. It contains carbon, hydrogen and oxygen.
• It also contains nitrogen, phosphorus and sulphur.
• It occurs in the solid state. It is of four types - peat, lignite, bituminous and anthracite.

In simple words: Coal is a solid fossil fuel composed mainly of carbon, hydrogen, and oxygen, along with nitrogen, phosphorus, and sulfur, found in four main types: peat, lignite, bituminous, and anthracite.

🎯 Exam Tip: Define coal as a fossil fuel and mention its elemental composition and the different types as classification criteria.

 

Question 8. What is Coke?
Answer:The pure coal that remains when coal gas has been taken away from coal, is called coke.In simple words: Coke is a pure carbon residue left after heating coal in the absence of air to remove volatile components like coal gas.

🎯 Exam Tip: Understand coke as a refined form of coal, specifically produced by heating coal without air, which increases its carbon content.

 

Question 9. Give the uses of Coal.
Answer:Uses of Coal are:

• Coal is used as fuel in factories and homes.
• Coal is used to obtain coke, coal gas and coal tar.
• Coal is used in thermal power plants for generation of electricity.

In simple words: Coal is primarily used as a fuel for heating homes and in industries, for producing coke, coal gas, and coal tar, and significantly for generating electricity in thermal power plants.

🎯 Exam Tip: List both direct (fuel, electricity generation) and indirect (production of other chemicals) uses of coal to show a comprehensive understanding.

 

Question 10. Give the uses of Coke.
Answer:Uses of Coke are:

• Used as domestic fuel.
• Coke is used as a reducing agent.
• Coke is used in production of water gas (CO + H₂) and producer gas (CO + H2 + CO2 + N2)

In simple words: Coke is used as a domestic fuel, a reducing agent in metallurgy, and a key raw material for producing water gas and producer gas.

🎯 Exam Tip: Emphasize coke's role as a reducing agent and in gas production, which differentiates its uses from raw coal.

 

Question 11. Name the types of coal and give the differences in them.
Answer:The four types of coal are Peat, Lignite, Bituminous and Anthracite.

Points of differences	Peat	Lignite	Bitumi-nous	Anthracite
(1) Formation step number	First	Second	Third	Last
(2) Carbon content	Less than 60%	60% to 70%	70% to 90%	about 95%
(3) Heat produced	Lowest of all the rest	More than peat but less than bituminous	More than lignite but less than anthracite	Highest of all the rest

In simple words: The four types of coal (Peat, Lignite, Bituminous, Anthracite) represent stages of coal formation, each with increasing carbon content and heat production, with peat being the least mature and anthracite the most.

🎯 Exam Tip: Memorize the order of coal types and correlate their carbon content and heat value; presenting this in a table format is excellent for clarity and scoring.

 

Question 12. Give the properties of covalent compounds.
Answer:Properties of covalent compounds:

• Covalent compounds have low melting points and boiling points.
• Generally they are insoluble in water and soluble in organic solvents.
• They are poor conductors of heat and electricity.

In simple words: Covalent compounds typically have low melting and boiling points, are insoluble in water but soluble in organic solvents, and are poor conductors of heat and electricity.

🎯 Exam Tip: Focus on the general trends of physical properties for covalent compounds: low melting/boiling points, solubility in organic solvents, and poor conductivity.

 

Question 13. What are saturated hydrocarbons? Give examples.
Answer:

• The hydrocarbons having only single bonds between carbon atoms are called saturated hydrocarbons.
• For example, ethane \((C_2H_6)\) which is \((CH_3 - CH_3)\), propane \((C_3H_8)\) which is \((CH_3 - CH_2 - CH_3)\).

In simple words: Saturated hydrocarbons are organic compounds consisting of carbon and hydrogen atoms, where all carbon-carbon bonds are single bonds, such as ethane and propane.

🎯 Exam Tip: The key defining feature of saturated hydrocarbons is the presence of only single bonds between carbon atoms; always include examples with their chemical formulas.

 

Question 14. What are unsaturated hydrocarbons? Give examples.
Answer:

• Some hydrocarbons have a multiple bond between two carbon atoms.
• A multiple bond can be a double bond or a triple bond.
• Hydrocarbons having at least one multiple bond are called unsaturated hydrocarbons.
• For example, ethene \((H_2C = CH_2)\), ethyne \((HC \equiv CH)\), propene \((CH_3 - CH = CH_2)\), propyne \((CH_3 - C \equiv CH)\).

In simple words: Unsaturated hydrocarbons are carbon and hydrogen compounds that contain at least one double or triple bond between carbon atoms, like ethene and ethyne.

🎯 Exam Tip: Clearly differentiate unsaturated hydrocarbons by the presence of double or triple carbon-carbon bonds and provide examples for both types of multiple bonds.

 

Question 15. Give the following information of carbon dioxide: Molecular formula, Molecular mass, Melting point, Percentage occurrence in air.
Answer:Molecular formula - \(\text{CO}_2\), Molecular mass - 44, Melting point -56.6 °C Percentage occurrence in air - 0.03%.In simple words: Carbon dioxide's molecular formula is \(\text{CO}_2\), its molecular mass is 44, it melts at -56.6 °C, and it makes up about 0.03% of the air.

🎯 Exam Tip: Be precise with numerical values for molecular mass, melting point, and atmospheric percentage, as these are exact data points.

 

Question 16. Give the physical and chemical properties of carbon dioxide.
Answer:Physical properties of carbon dioxide are:

• It is an odourless gas.
• It is a colourless gas.

Chemical properties of carbon dioxide are:

• It is non-combustible and does not support combustion.
• It turns lime water milky.
• It is fairly soluble in water and dissolves in water forming carbonic acid.
• It turns blue litmus red indicating it is acidic in nature.
• The colour of universal indicator turns orange/ yellow in \(\text{CO}_2\) indicating its pH value between 4 and 6, i.e. acidic in nature.

In simple words: Carbon dioxide is a colorless, odorless gas that is non-combustible, turns lime water milky, and is slightly soluble in water, forming carbonic acid which is acidic.

🎯 Exam Tip: Clearly distinguish between physical (observable without changing composition) and chemical (how it reacts) properties, providing specific examples for each.

 

Question 17. Give the uses of Carbon dioxide.
Answer:Uses of Carbon dioxide are:

• \(\text{CO}_2\) is used to make aerated drinks
• Solid carbon dioxide is used in cold storage and also to keep milk and milk products and frozen substances cool during transport. It is also used for getting special effects of a mist in dramas and movies.
• \(\text{CO}_2\) obtained by chemical reaction or kept under pressure is used in fire extinguishers.
• Liquified \(\text{CO}_2\) is used to remove caffeine from coffee.
• Liquid \(\text{CO}_2\) is used as solvent in modern eco-friendly dry cleaning.
• Plants use \(\text{CO}_2\) in air for photosynthesis.

In simple words: Carbon dioxide is used in aerated drinks, as solid dry ice for refrigeration and special effects, in fire extinguishers, for decaffeinating coffee, as an eco-friendly dry cleaning solvent, and is vital for plant photosynthesis.

🎯 Exam Tip: List a variety of uses covering different states of \(\text{CO}_2\) (gas, solid, liquid) and its roles in industrial, biological, and entertainment applications.

 

Question 18. Give the occurrence of methane.
Answer:The occurrence of methane is as follows:

• Methane occurs in natural gas to the extent of 87%.
• Decomposition of organic matter in the absence of air (anaerobic) produces methane.
• Methane is present in biogas.
• Methane is found in coal mines.
• Methane is found at the surface of marshy places which is why it is also called marsh gas.
• On heating a mixture of hydrogen and carbon monoxide gases at 300 °C in the presence of nickel (catalyst), methane gas is formed.
• Fractional distillation of natural gas gives methane in pure form.

In simple words: Methane is found naturally as a major component of natural gas (87%), is produced by anaerobic decomposition of organic matter, exists in biogas, coal mines, and marshy areas, and can be synthesized from hydrogen and carbon monoxide.

🎯 Exam Tip: When discussing occurrence, include both natural sources (like natural gas and marshes) and methods of generation (anaerobic decomposition, catalytic synthesis).

 

Question 19. Give the physical properties of methane.
Answer:Physical properties of methane are:

• Melting point of methane is (-182.5 °C).
• Boiling point of methane is (-161.5 °C).
• It is a colourless gas.
• The density of liquid methane is less than that of water.
• Methane is sparingly soluble in water. It is highly soluble in organic solvents like gasoline, ether and alcohol.
• Methane is in gaseous state at room temperature.

In simple words: Methane is a colorless gas at room temperature, with a melting point of -182.5 °C and a boiling point of -161.5 °C, sparingly soluble in water but highly soluble in organic solvents.

🎯 Exam Tip: Focus on key physical descriptors like state at room temperature, color, odor, and solubility, along with melting and boiling points.

 

Question 20. Give the uses of methane.
Answer:Uses of methane are:

• Methane in the form of natural gas is used in industries such as fabric mills, paper mills, food processing industry, petrol purification.
• Being the smallest hydrocarbon, the proportion of \(\text{CO}_2\) released in the combustion of methane is small and, therefore, it is used as a domestic fuel.
• Methane is used for production of organic compounds such as ethanol, methyl chloride, methylene chloride and acetylene.

In simple words: Methane is used as natural gas in various industries, as a clean domestic fuel due to its low \(\text{CO}_2\) emissions upon combustion, and as a raw material for synthesizing other organic compounds like ethanol and acetylene.

🎯 Exam Tip: Highlight methane's dual role as a fuel (emphasizing its clean-burning nature) and as a chemical feedstock for organic synthesis.

 

Question 21. How is methane formed? Give structural formula and electron dot model of methane.
Answer:

• Atomic number of carbon is 6. The electronic configuration of carbon is (2, 4). The valency of carbon is 4.
• Carbon atom can form four covalent bonds with other carbon atoms or atoms of different elements.
• When a carbon atom shares one electron each with four hydrogen atoms and forms four C-H bonds, a methane \((CH_4)\) molecule is formed.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र मीथेन \((CH_4)\) के संरचनात्मक सूत्र और इलेक्ट्रॉन बिंदु मॉडल को दर्शाता है। केंद्रीय कार्बन परमाणु चार हाइड्रोजन परमाणुओं से सहसंयोजक बंधों द्वारा जुड़ा होता है, जिससे एक चतुष्कोणीय आकार बनता है, जहां प्रत्येक रेखा एक सहसंयोजक बंध को दर्शाती है और बिंदु इलेक्ट्रॉनों को।In simple words: Methane is formed when a carbon atom, with its valency of 4, shares one electron each with four hydrogen atoms, creating four single covalent C-H bonds to complete its octet.

🎯 Exam Tip: Explain methane formation by detailing carbon's electronic configuration and its ability to form four covalent bonds, then accurately draw both the structural and electron dot formulas.

 

Question 22. What are organic and inorganic compounds?
Answer:Compounds obtained directly or indirectly from plants and animals are called organic compounds and compounds obtained from minerals are called inorganic compounds.In simple words: Organic compounds are carbon-based substances typically derived from living organisms, while inorganic compounds are generally those not containing carbon-hydrogen bonds, usually sourced from minerals.

🎯 Exam Tip: The classic distinction focuses on origin (living vs. non-living), but for a more chemical definition, emphasize the presence of carbon-hydrogen bonds in organic compounds.

 

Question 23. What is allotropy?
Answer:

• Allotropy - Some elements occur in nature in more than one form.
• The chemical properties of these different forms are the same but their physical properties are different.
• This property of elements is called allotropy.

In simple words: Allotropy is the property of some elements to exist in two or more different forms, called allotropes, which have identical chemical properties but distinct physical properties.

🎯 Exam Tip: Key points for defining allotropy are "same element," "different forms," "same chemical properties," and "different physical properties."

 

Question 24. What are basic organic compounds? What are they also called as?
Answer:

• The compounds formed from only carbon and hydrogen are called basic organic compounds.
• These are also called hydrocarbons.

In simple words: Basic organic compounds are those made exclusively from carbon and hydrogen atoms, commonly referred to as hydrocarbons.

🎯 Exam Tip: Define basic organic compounds by their elemental composition (only carbon and hydrogen) and their alternative name, hydrocarbons.

 

Question 1. Preparation of urea from Ammonium cyanate:
Answer:\(\text{NH}_4\text{CNO} \xrightarrow{\text{Heat}} \text{NH}_2\text{CONH}_2\) Ammonium Cyanate \(\implies\) Urea Organic compound Urea can be synthesized from an inorganic compound Ammonium cyanate.In simple words: Urea, an organic compound, is prepared by heating ammonium cyanate, an inorganic compound, in a rearrangement reaction.

🎯 Exam Tip: This reaction is historically significant as Wohler's synthesis; remember the reactants (ammonium cyanate) and product (urea) and that it involves heating.

 

Question 2. Coal when burnt in air
Answer:\(\text{C} + \text{O}_2 \implies \text{CO}_2\uparrow\) Carbon Oxygen \(\implies\) Carbon dioxide When coal is burnt in air, the carbon present in coal combines with oxygen present in air to form carbon dioxide gas.In simple words: When coal burns in air, its carbon reacts with oxygen to produce carbon dioxide gas.

🎯 Exam Tip: This is a simple combustion reaction. Ensure correct reactants (\(\text{C}\) and \(\text{O}_2\)) and product (\(\text{CO}_2\)), indicating the upward arrow for gas.

 

Question 3. Calcium carbonate reacts with dilute hydrochloric acid:
Answer:\(\text{CaCO}_3 + 2\text{HCl} \implies \text{CaCl}_2 + \text{H}_2\text{O} + \text{CO}_2\uparrow\) Calcium carbonate + Dilute hydrochloric acid \(\implies\) Calcium chloride + Water + Carbon dioxide When Calcium carbonate reacts with dilute hydrochloric add it forms Caldum chloride, water and Carbon dioxide gas is evolved.In simple words: Calcium carbonate reacts with dilute hydrochloric acid to produce calcium chloride, water, and carbon dioxide gas.

🎯 Exam Tip: This reaction is a classic test for carbonates (producing \(\text{CO}_2\)). Remember the gas (\(\text{CO}_2\)) and its upward arrow, indicating evolution.

 

Question 4. Carbon dioxide is passed through an aqueous solution of Sodium hydroxide:
Answer:\(\text{2NaOH} + \text{CO}_2 \implies \text{Na}_2\text{CO}_3 + \text{H}_2\text{O}\) Aqueous Sodium hydroxide + Carbon dioxide \(\implies\) Sodium carbonate + Water When Carbon dioxide gas is passed through an aqueous solution of Sodium hydroxide it forms Sodium carbonate and Water.In simple words: When carbon dioxide is passed through an aqueous sodium hydroxide solution, it reacts to form sodium carbonate and water.

🎯 Exam Tip: This is an acid-base reaction where acidic \(\text{CO}_2\) reacts with basic \(\text{NaOH}\). Ensure the reactants and products are correctly balanced.

 

Question 5. Carbon dioxide is passed through an aqueous solution of Sodium carbonate:
Answer:\(\text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2 \implies 2\text{NaHCO}_3\) Sodium carbonate + Water + Carbon dioxide \(\implies\) Sodium bicarbonate When carbon dioxide is passed through an aqueous solution of Sodium carbonate, it forms Sodium bicarbonate.In simple words: Passing carbon dioxide through an aqueous solution of sodium carbonate causes it to react and form sodium bicarbonate.

🎯 Exam Tip: This reaction shows the conversion of a normal carbonate to a bicarbonate; ensure the balanced equation correctly reflects the addition of \(\text{CO}_2\) and \(\text{H}_2\text{O}\).

 

Question 6. Carbon dioxide is passed through freshly prepared lime water for a short duration and then for longer duration:
Answer:\(\text{Ca(OH)}_2 + \text{CO}_2 \implies \text{H}_2\text{O} + \text{CaCO}_3\downarrow\) Calcium hydroxide (lime water) + Carbon dioxide \(\implies\) Water + Calcium carbonate (white) When Carbon dioxide is passed through freshly prepared lime water, it forms water and white precipitate of Calcium carbonate because of which lime water turns milky.
\(\text{CaCO}_3 + \text{H}_2\text{O} + \text{CO}_2 \implies \text{Ca(HCO}_3)_2\) Calcium carbonate + Water + Carbon dioxide \(\implies\) Calcium bicarbonate (Soluble) When Carbon dioxide is continuously passed through milky lime water, it forms Calcium bicarbonate which is soluble in water and therefore, water once again turns colourless.In simple words: Initially, carbon dioxide turns limewater milky by forming insoluble calcium carbonate, but with prolonged bubbling, the milkiness disappears as soluble calcium bicarbonate is formed.

🎯 Exam Tip: This is a crucial two-stage reaction often used to test for \(\text{CO}_2\). Remember both equations and the visual changes (milkiness then clearing) with the corresponding products.

 

Question 7. Carbon dioxide gas is dissolved in water.
Answer:\(\text{CO}_{2(g)} + \text{H}_2\text{O} \implies \text{H}_2\text{CO}_3\) Carbon dioxide + Water \(\implies\) Carbonic acid Carboh dioxide gas is fairly soluble in water, it dissolves in water under pressure to form Carbonic acid.In simple words: When carbon dioxide gas dissolves in water, especially under pressure, it forms carbonic acid, making the solution acidic.

🎯 Exam Tip: This reaction explains the acidity of carbonated drinks and rainwater. Note that \(\text{CO}_2\) is more soluble under pressure.

 

Question 8. Sodium bicarbonate reacts with dilute Sulphuric acid, (reaction in fire extinguisher):
Answer:\(2\text{NaHCO}_3 + \text{H}_2\text{SO}_4 \implies \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O} + 2\text{CO}_2\uparrow\) Sodium bicarbonate + Sulphuric acid \(\implies\) Sodium sulphate + Water + Carbon dioxide When Sodium bicarbonate reacts with dilute Sulphuric acid it forms Sodium sulphate, water and Carbon dioxide gas.In simple words: In a fire extinguisher, sodium bicarbonate reacts with dilute sulfuric acid to produce sodium sulfate, water, and crucially, carbon dioxide gas, which helps suppress fires.

🎯 Exam Tip: This reaction demonstrates how fire extinguishers generate \(\text{CO}_2\). Remember the reactants and products, and especially the role of \(\text{CO}_2\) in extinguishing fires.

 

Question 9. Methane gas is burnt in air:
Answer:\(\text{CH}_4 + 2\text{O}_2 \implies \text{CO}_2\uparrow + 2\text{H}_2\text{O} + \text{heat}\) Methane + Oxygen \(\implies\) Carbon dioxide + Water + heat Methane is highly inflammable, it burns in air with a bluish flame and combines with oxygen present in air to form Carbon dioxide and water. In these reaction 213 kcal/mol of heat is given out.In simple words: Methane, a highly flammable gas, burns completely in air, reacting with oxygen to produce carbon dioxide, water, and a significant amount of heat.

🎯 Exam Tip: This is a combustion reaction of methane. Ensure the equation is balanced, and mention the release of heat as it's a key characteristic of fuel combustion.

 

Question 10. Methane and Chlorine gases react with each other.
Answer:\(\text{CH}_4 + \text{Cl}_2 \xrightarrow{\text{Light}} \text{CH}_3\text{Cl} + \text{HCl}\) Methane + Chlorine \(\xrightarrow{\text{Light}}\) Methyl Chloride + Hydrogen Chloride Methane and chlorine gases react with each other at the temperature of 250 °C to 400 °C in presence of ultra voilet light and form mainly Methyl chloride (Chloromethane and ' Hydrogen chloride) This reaction is called Chlorination of methane.In simple words: Methane reacts with chlorine gas in the presence of light or heat to form methyl chloride (chloromethane) and hydrogen chloride through a substitution reaction called chlorination.

🎯 Exam Tip: Note the specific conditions (light or temperature) required for this substitution reaction, which is a fundamental concept in organic chemistry.

 

Question 11. Production of methane gas in biogas plant.
Answer:\(\text{CH}_3\text{COOH} \implies \text{CH}_4 + \text{CO}_2\uparrow\) Organic acid (Acetic acid) \(\implies\) Methane + Carbon dioxide In biogas plant, microbes act on the bio-degradable complex organic compounds and produce organic acids. The methanogenic bacteria act on the organic acids to produce Methane gas and Carbon dioxide gas.In simple words: In a biogas plant, microorganisms first break down complex organic matter into organic acids, which are then converted by methanogenic bacteria into methane and carbon dioxide.

🎯 Exam Tip: Understand this as a two-stage anaerobic digestion process. Focus on the role of microbes and the final products: methane and carbon dioxide.

 

Question 12. Production of water gas:
Answer:\(\text{C} + \text{H}_2\text{O} \implies \text{CO}\uparrow + \text{H}_2\uparrow\) Red hot coke + Super heated steam \(\implies\) Carbon monoxide + Hydrogen This gaseous product of carbon monoxide gas and hydrogen gas together is called as water gas.In simple words: Water gas, a mixture of carbon monoxide and hydrogen, is produced by passing superheated steam over red-hot coke.

🎯 Exam Tip: Remember the reactants (red-hot coke and superheated steam) and the products (carbon monoxide and hydrogen) which together constitute "water gas."

 

Question 1. Regular fire extinguisher.
Answer:

• A fire extinguisher contains Sodium bicarbonate powder. There is also dilute sulphuric acid placed in a glass capsule.
• On pressing the knob, the capsule breaks and sulphuric acid comes in contact with the sodium bicarbonate. These two react chemically to release \(\text{CO}_2\) which comes out.
• \(\text{CO}_2\) based fire extinguishers do not cause corrosion and are non-conductors of electricity. Therefore, they are used when electrical or electronic equipment catches fire.
• \(\text{CO}_2\) based fire extinguishers are used to extinguish small scale fire. It is beyond their capacity to extinguish a big fire.
• In modern fire extinguishers liquid and solid \(\text{CO}_2\) is filled under pressure. On reducing the pressure, it becomes gaseous and comes out forcefully through the horn-like hose pipe.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक सामान्य अग्निशामक की आंतरिक संरचना को दर्शाता है। इसमें एक नॉब, एक कैप्सूल, सल्फ्यूरिक एसिड और सोडियम बाइकार्बोनेट पाउडर होता है। नॉब दबाने पर एसिड बाइकार्बोनेट से प्रतिक्रिया करता है, जिससे आग बुझाने वाली कार्बन डाइऑक्साइड गैस निकलती है।In simple words: A regular fire extinguisher works by mixing sodium bicarbonate powder with dilute sulfuric acid upon activation, which produces carbon dioxide gas to suppress small fires, especially electrical ones, without causing corrosion.

🎯 Exam Tip: Focus on the chemical reaction between sodium bicarbonate and sulfuric acid, the production of \(\text{CO}_2\), and its properties (non-conductor, heavy, non-combustible) that make it effective for small electrical fires.

 

Question 2. Biogas plant.
Answer:

• Animal dung, dry leaves, wet garbage get decomposed by anaerobic microbes in a biogas plant.
• This produces methane gas, also called biogas.
• Biogas is a very cheap fuel option which meets the demand for cooking gas. It is also used for the production of electricity.
• Biogas contains about 55% to 60% methane and the rest is carbon dioxide.
• Biogas is a fuel which is convenient to use and, in addition to this, a very good manure is also produced as a side product of the process.
• Biogas production process - Production of biogas is an anaerobic process. It takes place in two stages.
(a) Production of acids - The microbes act on the biodegradable complex organic compound and produce organic acids. (b) Methane gas production - The methanogenic bacteria act on the organic acids to produce methane gas.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक बायोगैस संयंत्र की कार्यप्रणाली को दर्शाता है। इसमें एक मिश्रण टैंक होता है जहाँ पशुओं का गोबर और पानी मिलाया जाता है, जो फिर इनलेट चैंबर से डाइजेस्टर टैंक में जाता है। यहाँ अवायवीय जीवाणु जैविक पदार्थों को तोड़कर बायोगैस (मीथेन और कार्बन डाइऑक्साइड) बनाते हैं, जो एक पाइप के माध्यम से बाहर निकलती है, और बची हुई घोल को खाद के रूप में उपयोग किया जाता है।In simple words: A biogas plant decomposes organic waste using anaerobic microbes in a two-stage process: first, producing organic acids, then methanogenic bacteria convert these acids into biogas (primarily methane and carbon dioxide), which serves as a cheap fuel and also yields good manure.

🎯 Exam Tip: Describe the biogas plant as an anaerobic digestion system that converts organic waste into methane-rich biogas (fuel) and valuable manure, highlighting its two-stage microbial action.

 

Question 1. What happens when substances like milk, sugar, wool, dry leaves, hair and seeds are heated strongly in hard glass test tube?
Answer: When milk, sugar, wool, dry leaves, hair and seeds are heated strongly in hard glass test tube, they get charred and a black substance is left behind. This black substance is carbon.
In simple words: When organic substances like milk, sugar, and leaves are heated strongly, they decompose, leaving behind a black residue, which is carbon. This demonstrates carbon's presence in various organic materials.

🎯 Exam Tip: Understanding how organic substances char upon heating is a key indicator of carbon content and is important for practical chemistry observations.

Answer The Following Questions

 

Question 1. Take some milk in an evaporating dish. Heat the evaporating dish on a bunsen burner. What remains behind at the bottom of an evaporating dish on complete evaporation of the milk?
Answer:
• On complete evaporation of milk, a black residue is left behind.
• This residue is of carbon.
In simple words: When milk is heated to complete dryness, a black substance remains, which is a form of carbon. This shows that milk, being an organic substance, contains carbon.

🎯 Exam Tip: Knowing that organic matter leaves carbon upon heating is fundamental for identifying carbon in various substances.

 

Question 2. Take small samples of sugar, wool, dry leaves, hair, seeds, split pulses and plastic in separate test tubes. Heat each test tube and observe the changes taking place in the substances. What does the black substance in each test tube indicate?
Answer:
• On heating the above samples, they get charred and a black substance is left behind.
• The black substance is carbon.
In simple words: When various organic materials like sugar, wool, leaves, hair, seeds, pulses, and plastic are heated, they all turn black, indicating the presence of carbon as their fundamental component.

🎯 Exam Tip: This experiment highlights the pervasive presence of carbon in organic materials, a core concept in organic chemistry.

 

Question 3. Apparatus: Coal, match box, moist litmus paper, etc. Procedure: Ignite the coal. Hold the moist blue litmus paper over the gas released on igniting the coal. Note the observation.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक प्रयोग को दर्शाता है जहाँ एक Bunsen burner पर कोयले के एक टुकड़े को जलाया जा रहा है। जलते हुए कोयले के ऊपर एक नम नीले लिटमस पेपर को रखा गया है ताकि निकलने वाली गैस की प्रकृति का परीक्षण किया जा सके। यह सेटअप कोयले के दहन के उत्पादों और उनके अम्लीय या क्षारीय गुणों को समझने में मदद करता है।
(a) With which gas in the air does the coal react on igniting?
Answer: Coal reacts with oxygen gas present in the air, on igniting.
(b) What is the substance formed?
Answer: The substance formed is carbon dioxide.
(c) What change takes place in the litmus paper?
Answer: The moist blue litmus paper turns red.
(d) Write down the chemical reaction taking place in the above procedure.
Answer:
(i) Carbon combines with oxygen to form Carbon dioxide gas.
\( \text{C}_{\text{(Carbon)}} + \text{O}_{2\text{(Oxygen)}} \implies \text{CO}_{2\text{(Carbon dioxide)}}\uparrow \)
(ii) This CO2 combines with water present on moist blue litmus paper to form Carbonic acid which turns blue litmus to red.
\( \text{CO}_{2\text{(Carbon dioxide)}} + \text{H}_{2}\text{O}_{\text{(Water)}} \implies \text{H}_{2}\text{CO}_{3\text{(Carbonic acid)}} \)
In simple words: When coal burns, it reacts with oxygen to form carbon dioxide. Carbon dioxide then reacts with the water in moist blue litmus paper to form carbonic acid, which turns the litmus paper red, indicating its acidic nature.

🎯 Exam Tip: Remember the reaction of CO2 with water to form carbonic acid; this is a common test for carbon dioxide and a fundamental concept for understanding acid rain.

 

Question 4. Apparatus: Pencil, electrical wires, battery/ cell, small bulb, water, kerosene, test tube, lead pencils, etc. Procedure : Remove the lead from a pencil and arrange the apparatus as shown in the above diagram. Note your observations for the following.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक साधारण विद्युत परिपथ को दर्शाता है जिसका उपयोग पेंसिल के लीड (ग्रेफाइट) की चालकता का परीक्षण करने के लिए किया जाता है। इसमें एक बैटरी/सेल, एक बल्ब और तार जुड़े हुए हैं, जहाँ पेंसिल के लीड को परिपथ के एक हिस्से के रूप में शामिल किया गया है। यदि लीड विद्युत का चालक है, तो बल्ब जलेगा।
(a) What is the colour of lead in the pencil? .
Answer: The colour of the lead in the pencil is black as it is made from graphite which is an allotrophic form of carbon.
(b) Try to break lead with your hand.
Answer: The lead breaks easily as it is made up of graphite which is brittle in nature.
(c) Start the electric current in the circuit and observe. What did you find?
Answer: When we start the electric current in the circuit, the bulb in the circuit glows, indicating that the lead in the pencil is a good conductor of electricity.
(d) Take some water in a test tube. Take some kerosene in another test tube. Put lead dust in both the test tube. What did you observe?
Answer:
(i) Lead dust does not dissolve in water nor in kerosene.
(ii) It remains insoluble in both the test tubes.
In simple words: Pencil lead, made of graphite, is black, brittle, and conducts electricity, causing a bulb to glow in a circuit. It is insoluble in both water and kerosene. This demonstrates graphite's unique properties as an allotrope of carbon.

🎯 Exam Tip: This experiment is crucial for illustrating graphite's properties: its brittleness, insolubility, and especially its electrical conductivity, which distinguishes it from diamond.

 

Question 5. Apparatus : Test tube, straw, lime water, etc. Procedure: Take freshly prepared lime water in a test tube. Blow air in it for some time through the straw and observe the lime water. Note the observation.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक प्रयोग को दर्शाता है जहाँ एक टेस्ट ट्यूब में चूने का पानी (lime water) लिया गया है और एक स्ट्रॉ के माध्यम से उसमें हवा फूंकी जा रही है। यह प्रयोग यह जांचने के लिए किया जाता है कि फूंकी गई हवा में कार्बन डाइऑक्साइड मौजूद है या नहीं, क्योंकि कार्बन डाइऑक्साइड चूने के पानी को दूधिया कर देती है।
(a) What did you see?
Answer: When we blow air through the straw in freshly prepared lime water, it turns milky.
(b) What might be the reason behind the change?
Answer: Freshly prepared lime water is obtained by dissolving lime (CaO) in water (H2O).
\( \text{CaO}_{\text{(Lime)}} + \text{H}_{2}\text{O}_{\text{(Water)}} \implies \text{Ca(OH)}_{2\text{(Lime water)}} \)
When we blow air through the straw in lime water, carbon dioxide (CO2) present in the air reacts with lime water to form white precipitate (insoluble substance) of Calcium Carbonate (CaCO3) due to which lime water turns milky.
\( \text{Ca(OH)}_{2\text{(Lime water)}} + \text{CO}_{2\text{(Carbon dioxide)}} \implies \text{H}_{2}\text{O}_{\text{(Water)}} + \text{CaCO}_{3\downarrow\text{(Calcium Carbonate (White))}} \)
In simple words: Blowing air through limewater makes it milky because the carbon dioxide in our breath reacts with the calcium hydroxide in limewater to form insoluble calcium carbonate, which appears as a white precipitate.

🎯 Exam Tip: This is a classic test for carbon dioxide (CO2) and demonstrates a simple acid-base reaction forming a precipitate. Knowing the chemical equations involved is vital.

 

Question 6. With the help of a neat labelled diagram explain the laboratory preparation of Carbon dioxide gas.
Answer: The laboratory preparation of Carbon dioxide gas is as follows:
Apparatus : Retort stand, round bottom flask, thistle funnel, gas delivery tube, gas jars.
Chemicals: Calcium carbonate (Pieces of Shahabad tiles/marble pieces/limestone), dilute hydrochloric acid.
Procedure:
• Assemble the apparatus as shown in the figure. While assembling, place CaCO3 in the round bottom flask.
• Add dilute HCI in the flask through thistle funnel. See to it that the end of the funnel dips in the acid.
• CO2 is formed as a result of the reaction between CaCO3 and HCI. Collect this gas in four to five gas jars. The chemical equation of the above reaction is as follows.
\( \text{CaCO}_{3} + \text{2HCl} \implies \text{CaCl}_{2} + \text{H}_{2}\text{O} + \text{CO}_{2} \uparrow \)
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र कार्बन डाइऑक्साइड गैस के प्रयोगशाला में निर्माण के लिए एक मानक उपकरण सेटअप को दर्शाता है। इसमें एक रिटॉर्ट स्टैंड, एक गोल पेंदी वाला फ्लास्क, एक थिसल कीप और एक गैस डिलीवरी ट्यूब शामिल है जो गैस जार में हवा के ऊपर की ओर विस्थापन द्वारा CO2 को इकट्ठा करती है। थिसल कीप से हाइड्रोक्लोरिक एसिड को फ्लास्क में मौजूद कैल्शियम कार्बोनेट पर डाला जाता है ताकि प्रतिक्रिया शुरू हो सके।
In simple words: Carbon dioxide gas is prepared in the lab by reacting calcium carbonate (like marble chips) with dilute hydrochloric acid in a flask. The CO2 produced is collected by upward displacement of air in gas jars, and the reaction forms calcium chloride and water as byproducts.

🎯 Exam Tip: Familiarity with common laboratory preparations, including the apparatus, chemicals, procedure, and balanced chemical equation for CO2, is essential for both theoretical understanding and practical exams.