RBSE Solutions Class 10 Science Chapter 8 Carbon and its Compounds

I. Multiple Choice Questions:

Question 1. What is the bond angle in methane?
(a) 109°28'
(b) 120°
(c) 180°
(d) 105°
Answer: (a) 109°28'
In simple words: The atoms in a methane molecule are arranged in a specific way, and the angle between any two bonds is 109 degrees and 28 minutes. This tetrahedral shape is very common in organic chemistry.

🎯 Exam Tip: Remember that methane (CH4) has a tetrahedral geometry around the carbon atom, leading to a bond angle of approximately 109.5° (109°28'). This specific angle is a key characteristic of sp3 hybridized carbon.

Question 2. \( \text{C}_5\text{H}_{10} \) is the formula of which hydrocarbon?
(a) Pentane
(b) Pentene
(c) Pentyne
(d) Pentadiene
Answer: (b) Pentene
In simple words: The formula \( \text{C}_5\text{H}_{10} \) fits the general formula \( \text{C}_n\text{H}_{2n} \), which is for alkenes. Since it has 5 carbon atoms, it is called pentene, meaning an alkene with five carbons.

🎯 Exam Tip: To identify hydrocarbons from their molecular formula, remember the general formulas: alkanes \( (\text{C}_n\text{H}_{2n+2}) \), alkenes \( (\text{C}_n\text{H}_{2n}) \), and alkynes \( (\text{C}_n\text{H}_{2n-2}) \). Match the given formula to the correct series.

Question 3. What is the formula of Freon-11?
(a) \( \text{CFCl}_3 \)
(b) \( \text{C}_2\text{F}_2\text{Cl}_4 \)
(c) \( \text{CF}_2\text{Cl}_2 \)
(d) \( \text{C}_2\text{F}_4\text{Cl} \)
Answer: (a) \( \text{CFCl}_3 \)
In simple words: Freon-11 is a type of chlorofluorocarbon (CFC) that has one carbon atom, one fluorine atom, and three chlorine atoms. These compounds were widely used but are now restricted due to their impact on the ozone layer.

🎯 Exam Tip: Freon nomenclature can be tricky. Freon-11 (or CFC-11) has the formula \( \text{CFCl}_3 \). Remembering a few common Freon formulas, like Freon-12 (\( \text{CF}_2\text{Cl}_2 \)), helps in distinguishing them.

Question 5. Which allotrope of carbon is a good conductor of electricity?
(a) Diamond
(b) Graphite
(c) Fullerene
(d) Coke
Answer: (b) Graphite
In simple words: Graphite is special because its carbon atoms are arranged in layers, and some electrons are free to move. This movement allows electricity to pass through easily, unlike diamond where all electrons are fixed in bonds.

🎯 Exam Tip: Understand the structure of carbon allotropes. Graphite's hexagonal layers with delocalized electrons explain its conductivity and softness, while diamond's rigid tetrahedral structure explains its hardness and insulating properties.

Question 6. For improving the tensile strength and quality of natural rubber, it is heated with sulphur. What is the name of this process?
(a) Polymerization
(b) Saponification
(c) Vulcanisation
(d) Equalization
Answer: (c) Vulcanisation
In simple words: When natural rubber is heated with sulfur, it becomes much stronger and more useful. This special chemical process is known as vulcanization, which makes rubber more durable.

🎯 Exam Tip: Vulcanisation is a crucial process for enhancing rubber properties. Knowing the name of the process and the key reactant (sulphur) is important for questions on polymer modification.

Question 7. What is the prefix if number of carbon atoms is 3?
(a) Eth-
(b) Prop-
(c) But-
(d) Pent-
Answer: (b) Prop-
In simple words: In naming organic compounds, each number of carbon atoms has a specific prefix. For three carbon atoms, the prefix "prop-" is always used, as seen in propane or propene.

🎯 Exam Tip: Memorize the prefixes for the first ten carbon chains (meth-, eth-, prop-, but-, pent-, hex-, hept-, oct-, non-, dec-) as they are fundamental to IUPAC nomenclature.

Carbon And Its Compounds Very Short Answer Type Questions

Question 9. Write the general formulae of alkane, alkene and alkyne.
Answer: The general formulas for these hydrocarbon families are:
Alkane: \( \text{C}_n\text{H}_{2n+2} \)
Alkene: \( \text{C}_n\text{H}_{2n} \)
Alkyne: \( \text{C}_n\text{H}_{2n-2} \)
In simple words: These formulas help us know how many hydrogen atoms are connected to carbon atoms in different types of carbon chains. They show if the chain has only single bonds (alkane), one double bond (alkene), or one triple bond (alkyne).

🎯 Exam Tip: These general formulas are essential for understanding and predicting the properties of hydrocarbons. Practice applying them to various 'n' values to check your understanding.

Question 10. Hydrocarbons are made up of which elements?
Answer: Hydrocarbons are made up of hydrogen and carbon elements. These are the two basic elements found in all organic compounds that make up fuel and many other materials.
In simple words: Hydrocarbons only contain hydrogen and carbon atoms.

🎯 Exam Tip: The name "hydrocarbon" itself gives a clue about its composition: "hydro" refers to hydrogen and "carbon" refers to carbon.

Question 11. Write the full form of IUPAC.
Answer: The full form of IUPAC is International Union of Pure & Applied Chemistry. This organization sets the rules for naming chemical compounds worldwide, ensuring clarity and consistency.
In simple words: IUPAC is an international group that makes rules for how we name chemicals so everyone understands them.

🎯 Exam Tip: Knowing the full form of IUPAC is important, but more crucially, understand that its rules (IUPAC nomenclature) provide a systematic way to name organic compounds, avoiding confusion.

Question 12. Define vulcanization.
Answer: Vulcanization is the process where natural rubber is heated with sulphur. This heating improves the rubber's tensile strength and overall quality, making it more durable and elastic. The sulphur creates cross-links between the rubber polymer chains, which gives it better properties.
In simple words: Vulcanization makes natural rubber stronger by heating it with sulfur.

🎯 Exam Tip: When defining a process like vulcanization, clearly mention the key reactant (sulphur) and the main benefits (improved strength and quality) to score full marks.

Question 13. What could be the total number of carbon atoms in fullerene?
Answer: The number of carbon atoms in fullerene can be 60, 70, or more. The most well-known fullerene is Buckminsterfullerene, which contains 60 carbon atoms in a soccer ball-like structure.
In simple words: Fullerene molecules can have 60, 70, or even more carbon atoms.

🎯 Exam Tip: Remember that fullerenes are a class of carbon allotropes, not just one specific molecule. C60 is the most common example, but other fullerenes exist with varying numbers of carbon atoms.

Question 15. What is Freon.
Answer: Freons are compounds formed when chlorine and fluorine atoms combine with carbon. These compounds are also known as chlorofluorocarbons, or poly-chloro-fluoroalkanes. They were once widely used as refrigerants and propellants, but their use is now restricted because they damage the ozone layer.
In simple words: Freons are chemicals made of carbon, chlorine, and fluorine, used in fridges and sprays, but they harm the ozone layer.

🎯 Exam Tip: When defining Freon, emphasize its composition (carbon, chlorine, fluorine) and its classification as a chlorofluorocarbon (CFC). Also, briefly mention its historical uses and environmental impact.

Question 16. Which scientist was the first to synthesize organic compound?
Answer: Friedrich Wohler was the first scientist to synthesize an organic compound. In 1828, he synthesized urea from inorganic compounds, challenging the vital force theory that organic compounds could only be produced by living organisms.
In simple words: Friedrich Wohler was the first scientist to make an organic compound in a lab.

🎯 Exam Tip: Remember Wohler's synthesis of urea as a landmark event in chemistry, as it disproved the "vital force" theory and paved the way for modern organic chemistry.

Question 17. Write the full form of CNG.
Answer: The full form of CNG is Compressed Natural Gas. It is a fuel gas that is a mixture of hydrocarbons, mainly methane, and is stored under high pressure.
In simple words: CNG stands for Compressed Natural Gas.

🎯 Exam Tip: CNG is an important alternative fuel. Understand that it is primarily methane and is used in compressed form, making it a cleaner burning fuel than gasoline or diesel.

Question 18. Orion is made by polymerization of which molecule?
Answer: Orion (likely an OCR error for Orlon, a type of acrylic fiber) is made by the polymerization of acrylonitrile monomer. Acrylonitrile monomers link together to form long polymer chains, creating acrylic fibers.
In simple words: Orion (Orlon) is made when many acrylonitrile molecules join together.

🎯 Exam Tip: For polymerization questions, identify the monomer unit (the building block) that forms the polymer. In this case, acrylonitrile is the monomer for acrylic polymers like Orlon.

Question 19. Write the names of allotropes of carbon.
Answer: The main allotropes of carbon are diamond, graphite, and fullerene. These forms have different physical properties because their carbon atoms are arranged differently, even though they are all made of pure carbon.
In simple words: Carbon can exist in different forms like diamond, graphite, and fullerene.

🎯 Exam Tip: Be able to list and distinguish the major allotropes of carbon, and recall their key physical properties and general structures.

Question 20. Write IUPAC name of isobutane.
Answer: The IUPAC name of isobutane is Methylpropane. Isobutane is a common name for a branched alkane, but Methylpropane is its systematic name according to IUPAC rules, indicating a three-carbon chain with a methyl group. There are four carbons in total, but the longest continuous chain is three carbons long.
In simple words: Isobutane's official chemical name is Methylpropane.

🎯 Exam Tip: When naming branched alkanes, always find the longest continuous carbon chain first, then identify the substituents and their positions. Common names like 'iso' and 'neo' are often recognized but the IUPAC name is preferred.

Question 22. PVC is made by polymerization of which molecule?
Answer: PVC, which stands for Polyvinyl Chloride, is made by the polymerization of vinyl chloride molecules. Many vinyl chloride units join together to form the long polymer chain of PVC, a widely used plastic.
In simple words: PVC is made from many small vinyl chloride molecules joining up.

🎯 Exam Tip: For synthetic polymers, identify both the full name of the polymer (e.g., Polyvinyl Chloride) and its corresponding monomer (e.g., vinyl chloride). This demonstrates a full understanding of the polymerization process.

Carbon And Its Compounds Short Answer Type Questions

Question 23. Write any three differences in properties of diamond and graphite.
Answer: Here are three differences between diamond and graphite:

In simple words: Diamond is very hard, clear, and does not conduct electricity, while graphite is soft, grey, and conducts electricity well.

🎯 Exam Tip: When comparing allotropes, always link their physical properties directly to their atomic structure. For instance, diamond's hardness comes from its rigid 3D network, while graphite's conductivity comes from delocalized electrons in its layered structure.

Question 24. What do you understand by catenation of carbon atom?
Answer: Catenation is the unique ability of carbon atoms to combine with other carbon atoms to form long chains, branched chains, or cyclic structures. This property allows carbon to create a vast number of large and complex molecules, which is fundamental to organic chemistry. This self-linking ability is strong due to the carbon-carbon bond strength.
In simple words: Catenation is when carbon atoms link up with each other in long chains or rings.

🎯 Exam Tip: Catenation is a defining characteristic of carbon. When defining it, emphasize both the "self-linking" aspect and the resulting "large and complex molecules" (chains, branches, rings).

Question 25. Write IUPAC name and structural formula of following:
(a) \( \text{C}_5\text{H}_{12} \)
(b) \( \text{C}_4\text{H}_8 \)
(C) \( \text{C}_3\text{H}_4 \)
Answer:
(c) \( \text{CH}_2\text{Cl}-\text{CH}_2-\text{CH}_2\text{Cl} \) (1,3-dichloropropane)
(d) \( \text{CH}_3-\text{CH}_2-\text{CH}(\text{C}_2\text{H}_5)-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3 \) (3-ethyl-4-methylhexane)
(e) \( \text{CH}_2=\text{CH}-\text{CH}(\text{CH}_3)-\text{CH}_3 \) (3-methyl-1-butene)
In simple words: To name a compound, first count the longest chain of carbon atoms. Then, identify any groups attached to this chain and their positions. The structural formula shows how all the atoms are connected.

🎯 Exam Tip: For IUPAC naming, always identify the longest carbon chain first, then number the chain to give substituents the lowest possible numbers. Pay close attention to double/triple bonds and functional groups.

Question 26. Write any two uses of Freon.
Answer: Two common uses of Freon are:
(i) As an inert solvent: Freons can dissolve many substances without reacting with them, making them useful in certain cleaning processes.
(ii) As a coolant in refrigerators and cold storage: Freons were historically widely used in cooling systems because they evaporate and condense easily, transferring heat efficiently.
In simple words: Freons were used as safe cleaning liquids and to make fridges cool.

🎯 Exam Tip: While Freons have environmental concerns, their historical uses (refrigerants, aerosols, solvents) are important to know. Focus on their physical properties that made them suitable for these applications.

Question 27. Why CNG is better than LPG as a fuel?
Answer: CNG is considered better than LPG as a fuel for several reasons. Firstly, CNG is lighter than air, so if there's a leak, it disperses upwards into the atmosphere, reducing the risk of fire or explosion. LPG, being heavier, tends to settle on the ground, creating a higher hazard. Secondly, CNG has a lower carbon content, leading to a more complete combustion and producing negligible amounts of harmful carbon monoxide and carbon dioxide compared to LPG. This makes CNG a more environmentally friendly fuel option. CNG's cleaner burning also results in less engine wear over time.
In simple words: CNG is better because it is lighter and floats away if it leaks, making it safer. Also, it burns cleaner and produces less pollution than LPG.

🎯 Exam Tip: When comparing fuels like CNG and LPG, focus on safety aspects (density relative to air) and environmental impact (combustion products). These are key differentiating factors.

Question 28. Diamond is hard but graphite is soft. Why?
Answer: Diamond is very hard because each carbon atom is strongly bonded to four other carbon atoms in a rigid, three-dimensional tetrahedral arrangement. This creates a very strong and stable network. In contrast, graphite is soft because each carbon atom is bonded to only three other carbon atoms, forming flat hexagonal sheets. These sheets are held together by weak forces, allowing them to easily slide past each other. This layered structure makes graphite soft and slippery.
In simple words: Diamond is hard because its carbon atoms are locked in a strong 3D structure. Graphite is soft because its carbon atoms are in layers that can easily slide over each other.

🎯 Exam Tip: Always explain the differences in properties of allotropes by referring to their distinct crystal structures and the types of bonding present. For carbon, the number of bonds per atom and the arrangement are crucial.

Question 29. Write any four characteristics of fullerene.
Answer: Here are four characteristics of fullerene:

• It appears like a football due to its spherical or ellipsoidal shape.
• A molecule of fullerene typically contains 60, 70, or more atoms of carbon, arranged in a cage-like structure.
• \( \text{C}_{60} \) (Buckminsterfullerene) is generally a bad conductor of electricity because its electrons are mostly localized within the molecular cage.
• Some fullerenes can act as superconductors at high temperatures when appropriately doped, exhibiting unique electrical properties.

In simple words: Fullerenes look like tiny footballs, can have many carbon atoms, usually don't conduct electricity well, but can sometimes become superconductors.

🎯 Exam Tip: When describing fullerenes, highlight their unique cage-like structure, variable carbon atom count (with \( \text{C}_{60} \) as the prime example), and their electrical properties, which can vary.

Carbon And Its Compounds Long Answer Type Questions

Question 31. What are the uses of graphite?
Answer: Graphite has several important uses due to its unique properties:

• Used in making pencils: The softness and ability of its layers to slide make it ideal for lead in pencils.
• Used as a dry lubricant: In machinery, it reduces friction without the need for oil, especially at high temperatures.
• For making electrodes: Its electrical conductivity makes it suitable for electrodes in batteries and electrolysis.
• For polishing iron articles: Its fine particles can give a smooth finish to metal surfaces.
• As a moderator in nuclear furnaces (reactors): It helps to slow down neutrons in nuclear reactors.

In simple words: Graphite is used in pencils, as a slippery powder to make machines run smoothly, in electric parts, for polishing, and to control nuclear reactions.

🎯 Exam Tip: When listing uses of a substance, try to relate each use back to a specific physical or chemical property of that substance. For graphite, its softness, slipperiness, and conductivity are key.

Question 32. Write main characteristics of carbon atom.
Answer: The main characteristics of a carbon atom are:

• Valency of carbon atom is 4: Carbon is tetravalent, meaning it can form four chemical bonds with other atoms, allowing for a wide variety of compounds.
• Carbon can make single, double, and triple bonds with other atoms: This versatility enables carbon to form diverse structures, from simple alkanes with single bonds to alkenes with double bonds and alkynes with triple bonds.
• Catenation: Carbon atoms have the unique ability to link with other carbon atoms to form long chains, branched structures, and rings, which is crucial for creating large organic molecules.
• Isomerism: Carbon compounds can exist as isomers, meaning they have the same molecular formula but different structural arrangements and properties.

In simple words: Carbon atoms can make four bonds, they can form single, double, or triple bonds, they can link together in long chains, and they can make different shapes with the same atoms.

🎯 Exam Tip: The tetravalency and catenation are the most important characteristics explaining carbon's ability to form a vast number of organic compounds. Ensure you can describe these clearly.

Question 34. What are plastics? Write the names of polymers of main plastics.
Answer: Plastics are materials made from polymers, which are large molecules formed by joining many smaller organic molecules (monomers). Plastics can be molded into various solid objects when soft and then retain their shape when hardened. They are widely used due to their versatility and durability.
Some examples of main plastics (polymers) include:

• Polyvinyl Chloride (PVC)
• Polythene (Polyethylene)
• Polystyrene

In simple words: Plastics are materials made of long chains of small organic molecules that can be shaped easily. Common plastics are PVC, polythene, and polystyrene.

🎯 Exam Tip: When defining plastics, mention their polymeric nature and moldability. When listing examples, try to include the full name along with the common abbreviation (e.g., Polyvinyl Chloride (PVC)).

Question 35. What is the utility of diamond and graphite?
Answer: Diamond and graphite, despite both being carbon allotropes, have distinct utilities due to their unique properties:
Uses of diamond:

• It is used for making jewellery because of its exceptional brilliance and sparkle.
• It is used for making cutting instruments for glass and rocks due to its extreme hardness.

Uses of graphite:

• It is used for making pencils (as 'lead') due to its softness and slippery nature.
• It is used as a lubricant due to its layered structure allowing layers to slide past each other easily.

In simple words: Diamond is used in jewelry and for cutting because it's super hard. Graphite is used in pencils and as a smooth, slippery material for machines because it's soft.

🎯 Exam Tip: When discussing the utility of substances, always link the use to a specific property. For diamond, it's hardness and luster; for graphite, it's softness, slipperiness, and conductivity.

Question 36. Explain the nomenclature of Freons.
Answer: The nomenclature of Freons (chlorofluorocarbons) follows a specific numbering system to indicate the number of carbon, hydrogen, and fluorine atoms in the molecular formula. The Freon number is represented as Freon-xyz, where:

• 'x' = number of carbon atoms - 1
• 'y' = number of hydrogen atoms + 1
• 'z' = number of fluorine atoms

For example, for Freon-11 (\( \text{CFCl}_3 \)):
Carbon atoms = 1, so \( x = 1 - 1 = 0 \).
Hydrogen atoms = 0, so \( y = 0 + 1 = 1 \).
Fluorine atoms = 1, so \( z = 1 \).
This results in Freon-011, which is commonly written as Freon-11. The remaining bonds are occupied by chlorine atoms (4 - 1 (for F) = 3 (for Cl)).
In simple words: Freons are named using numbers (like Freon-11). These numbers tell us how many carbon, hydrogen, and fluorine atoms are in the molecule using a simple code.

🎯 Exam Tip: Understanding the 'xyz' rule for Freon nomenclature is crucial. Practice applying it to common Freons like Freon-11 and Freon-12 to solidify your understanding.

Question 38. Write short notes on following:
(a) Freon
(b) CNG
(c) Natural rubber
Answer:
(a) **Freon:** When carbon atoms combine with chlorine and fluorine, the resulting compounds are called chlorofluorocarbons, commonly known as Freons. A poly-chloro-fluoroalkane is a type of Freon. For example, Freon-11 (\( \text{CFCl}_3 \)) can be produced by reacting carbon tetrachloride with hydrogen fluoride in the presence of antimony pentachloride catalyst. Freons were widely used as refrigerants and propellants but are now restricted due to their role in ozone depletion.
(c) **Natural Rubber:** Natural rubber is a polymer derived from latex, a milky sap produced by certain trees, primarily the rubber tree. The monomer unit of natural rubber is isoprene. Initially, natural rubber is highly elastic and has low tensile strength. To improve its properties like strength, elasticity, and durability, it undergoes a process called vulcanization, which involves heating it with sulphur. Acetic acid is often added to latex to cause it to coagulate and solidify.
In simple words: (a) Freon is a chemical made of carbon, chlorine, and fluorine, used for cooling but bad for the ozone. (c) Natural rubber comes from tree sap and is made stronger by adding sulfur through a process called vulcanization.

🎯 Exam Tip: For short notes, provide a concise definition, key properties or components, and any notable applications or environmental considerations. For Freon, mention its composition and environmental impact; for natural rubber, its source, monomer, and the importance of vulcanization.

Question 39. Answer the following:
(a) Write the rules of nomenclature of alkane.
(b) Write the formulae of following:
(1) Neopentane
(2) Isopentane
(3) 1,3-dichloropropane
(4) 3-ethyl-4-methyl hexane
(5) 3-methyl-l-butene
Answer:
(a) The rules for the nomenclature of alkanes are:

• The longest continuous carbon chain is selected as the parent chain. Any groups not part of this chain are called substituents.
• If there are two or more chains of the same length, the chain with the greater number of substituents is chosen as the parent chain.
• Substituents are named first, and prefixes (like methyl, ethyl) are written in alphabetical order.
• If the same substituent appears multiple times, prefixes like mono-, di-, tri-, tetra-, penta- are used to indicate the number of times it appears.
• Numbers indicating the positions of substituents are separated by commas, and a hyphen is used between a number and a name.

(b) The structural formulas provided as examples are:
(c) \( \text{CH}_2\text{Cl}-\text{CH}_2-\text{CH}_2\text{Cl} \)
(d) \( \text{CH}_3-\text{CH}_2-\text{CH}(\text{C}_2\text{H}_5)-\text{CH}(\text{CH}_3)-\text{CH}_2-\text{CH}_3 \)
(e) \( \text{CH}_2=\text{CH}-\text{CH}(\text{CH}_3)-\text{CH}_3 \)
In simple words: (a) When naming alkanes, first find the longest carbon chain. Then, name and number any attached groups. If there are many of the same group, use words like 'di' or 'tri'. (b) The formulas show how atoms are connected.

🎯 Exam Tip: Mastering IUPAC rules for alkanes is fundamental. Practice naming and drawing structures for various branched alkanes, paying close attention to chain selection, numbering, and alphabetical order of substituents.

Carbon And Its Compounds Additional Questions Solved

Question 1. The isomeric pair is
(a) ethane and propane
(b) propane and butane
(c) ethane and butane
(d) butane and 2-methyl propane
Answer: (d) butane and 2-methyl propane
In simple words: Isomers are compounds that have the same total number of each type of atom but are arranged differently. Butane (\( \text{C}_4\text{H}_{10} \)) and 2-methyl propane (also \( \text{C}_4\text{H}_{10} \)) are isomers because they share the same molecular formula but have different structures.

🎯 Exam Tip: Isomers have the same molecular formula but different structural formulas. Always count the total number of carbon and hydrogen atoms in each option to check for the same molecular formula before comparing structures.

Question 2. The structural formula of ethyl ethanoate is
(a) \( \text{CH}_3-\text{C}(=\text{O})-\text{OCH}_3 \)
(b) \( \text{CH}_3-\text{C}(=\text{O})-\text{OCH}_2\text{CH}_3 \)
(C) \( \text{CH}_3-\text{CH}_2-\text{C}(=\text{O})-\text{OCH}_2\text{CH}_3 \)
Answer:
In simple words: (No answer provided in the source.)

🎯 Exam Tip: For esters, the 'ethyl' part comes from the alcohol (ethanol), and the 'ethanoate' part comes from the carboxylic acid (ethanoic acid). The \( \text{-COO-} \) group is characteristic of esters.

Question 3. Identify the product formed when methane reacts with chlorine in the presence of sunlight is
(a) \( \text{C}_2\text{Cl}_6 \)
(b) \( \text{CH}_3\text{Cl} \)
(c) \( \text{CHCl}_4 \)
(d) None of the options
Answer: (b) \( \text{CH}_3\text{Cl} \)
In simple words: When methane and chlorine mix under sunlight, a hydrogen atom in methane is replaced by a chlorine atom, forming chloromethane. This is the first step in a series of substitution reactions.

🎯 Exam Tip: Remember that the reaction between alkanes and halogens (like chlorine) in the presence of sunlight is a free-radical substitution reaction. The reaction can proceed further to form di-, tri-, and tetra-substituted products.

Question 4. Which is denatured spirit?
(a) ethanol only
(b) ethanol and methanol (50%)
(c) ethanol and methanol (5%)
(d) methanol only
Answer: (c) ethanol and methanol (5%)
In simple words: Denatured spirit is mainly ethanol with a small amount of methanol added to make it unsuitable for drinking, usually for industrial purposes.

🎯 Exam Tip: Denaturing alcohol involves adding substances (like methanol) to ethanol to make it poisonous or unpalatable, preventing its consumption and making it tax-free for industrial use.

Question 5. According to IUPAC system, the correct name of the organic compound is
\( \text{CH}_3-\text{CH}(\text{Br})-\text{CH}_2-\text{C}(=\text{O})-\text{OH} \)
(a) 2-bromobutanoic acid
(b) 2-bromobutysis acid
(c) 3-bromobutanoic acid
(d) 3-bromo-2-hydroxybutan-2-one
Answer: (c) 3-bromobutanoic acid
In simple words: The compound has a four-carbon chain with a carboxylic acid group at one end and a bromine atom attached to the third carbon atom. So, it's 3-bromobutanoic acid.

🎯 Exam Tip: When naming carboxylic acids, the carbon of the \( \text{-COOH} \) group is always carbon number 1. Number the chain from this end to give substituents the lowest possible numbers.

Question 7. Vinegar is a solution of
(a) 30% - 40% acetic acid in alcohol
(b) 5% - 8% acetic acid in alcohol
(c) 5% - 8% acetic acid in water
(d) 15% - 20% acetic acid in water
Answer: (c) 5% - 8% acetic acid in water
In simple words: Vinegar is a dilute solution of acetic acid (also known as ethanoic acid) in water, typically containing 5% to 8% acetic acid.

🎯 Exam Tip: Remember the common name and chemical name for acetic acid (ethanoic acid) and its concentration range in household vinegar. This is a basic but frequently asked fact.

Question 8. The correct electron dot structure of a water molecule is
(a) \( \text{H}:\dot{\text{O}}:\dot{\text{O}}:\dot{\text{O}}:\text{H} \)
(b) \( \text{H}:\dot{\text{O}}:\text{H} \)
(c) \( \text{H}:\ddot{\text{O}}:\text{H} \)
(d) \( \text{H}:\dot{\text{O}}:\text{H} \)
Answer: (c) \( \text{H}:\ddot{\text{O}}:\text{H} \)
In simple words: In a water molecule, the oxygen atom shares one electron pair with each hydrogen atom. It also has two lone pairs of electrons that are not shared, making it a bent shape.

🎯 Exam Tip: When drawing electron dot structures, ensure all valence electrons are accounted for, both in bonding pairs and lone pairs. For water, oxygen has six valence electrons, forming two single bonds and having two lone pairs.

Question 9. Bromine reacts with saturated hydrocarbon at room temperature in the
(a) absence of sunlight
(b) presence of water
(c) presence of sunlight
(d) presence of hydrochloric acid
Answer: (c) presence of sunlight
In simple words: Saturated hydrocarbons (like alkanes) do not react easily. For them to react with halogens like bromine, they need extra energy, which is provided by sunlight, in a process called free-radical substitution.

🎯 Exam Tip: Recall the conditions for halogenation of alkanes. UV light or high temperatures are required to initiate the free-radical substitution mechanism, as alkanes are generally unreactive.

Question 11. Identify the correct way of numbering an organic compound (according to IUPAC).
(a) \( \text{CH}_3-\text{CH}_2-\text{CH}-\text{CH}_2-\text{CH}_3 \)
\( \quad\quad\quad \text{|} \)
\( \quad\quad\quad \text{C-H} \)
\( \quad\quad\quad \text{||} \)
\( \quad\quad\quad \text{O} \)
(b) \( \text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_3 \)
\( \quad\quad\quad \text{|} \)
\( \quad\quad\quad \text{C-H} \)
\( \quad\quad\quad \text{||} \)
\( \quad\quad\quad \text{O} \)
(c) \( \text{CH}_3-\text{CH}_2-\text{CH}-\text{CH}_2-\text{CH}_3 \)
\( \quad\quad\quad \text{|} \)
\( \quad\quad\quad \text{O} \)
(d) \( \text{CH}_3-\text{CH}_2-\text{CH}-\text{CH}_2-\text{CH}_3 \)
\( \quad\quad\quad \text{|} \)
\( \quad\quad\quad \text{C-H} \)
\( \quad\quad\quad \text{||} \)
\( \quad\quad\quad \text{O} \)
Answer: (a)
\( \text{CH}_3-\text{CH}_2-\text{CH}-\text{CH}_2-\text{CH}_3 \)
\( \quad\quad\quad \text{|} \)
\( \quad\quad\quad \text{C-H} \)
\( \quad\quad\quad \text{||} \)
\( \quad\quad\quad \text{O} \)
In simple words: In IUPAC naming, you must find the longest carbon chain that includes the functional group and number it so the functional group gets the lowest possible number. Option (a) correctly numbers the chain to give the carbonyl carbon the lowest position.

🎯 Exam Tip: Always prioritize the functional group for the lowest possible number when naming organic compounds according to IUPAC rules.

Question 13. The upper and lower homologue of \( \text{C}_2\text{H}_5\text{OH} \) are respectively
(a) methyl alcohol and butyl alcohol
(b) ethyl alcohol and propyl alcohol
(c) butyl alcohol and propyl alcohol
(d) propyl alcohol and methyl alcohol
Answer: (d) propyl alcohol and methyl alcohol
In simple words: Homologues are compounds in the same series that differ by a \( \text{CH}_2 \) unit. For ethanol (\( \text{C}_2\text{H}_5\text{OH} \)), the lower homologue has one less carbon (methyl alcohol, \( \text{CH}_3\text{OH} \)), and the upper homologue has one more carbon (propyl alcohol, \( \text{C}_3\text{H}_7\text{OH} \)).

🎯 Exam Tip: Remember that a homologous series increases or decreases by a \( \text{CH}_2 \) unit when identifying adjacent members.

Question 14. Ethanoic acid was added to sodium carbonate solution and the gas evolved was tested with a burning splinter. The following four observations were reported. Identify the correct observation.
(a) The gas burns with pop sound and the flame gets extinguished
(b) The gas does not burn but the splinter burns with pop sound
(c) The flame extinguishes and the gas does not burn.
(d) The gas burns with a blue flame and the splinter burns brightly
Answer: (c) The flame extinguishes and the gas does not burn.
In simple words: When ethanoic acid reacts with sodium carbonate, it makes carbon dioxide gas. Carbon dioxide does not burn, and it puts out flames, which is why the burning splinter would stop burning.

🎯 Exam Tip: Recall the standard test for carbon dioxide gas: it extinguishes a burning splint, unlike hydrogen which burns with a pop sound.

Question 15. Which of the following is not a straight chain?
(a) \( \text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2 \)
\( \quad\quad\quad\quad\quad\quad \text{|} \)
\( \quad\quad\quad\quad\quad\quad \text{CH}_2 \)
Answer: (a)
\( \text{CH}_3-\text{CH}_2-\text{CH}_2-\text{CH}_2 \)
\( \quad\quad\quad\quad\quad\quad \text{|} \)
\( \quad\quad\quad\quad\quad\quad \text{CH}_2 \)
In simple words: A straight chain hydrocarbon has all its carbon atoms linked one after another without any branches. The structure in option (a) has a carbon atom branching off the main chain, making it a branched chain, not a straight one.

🎯 Exam Tip: Always look for any carbon atoms that are attached to more than two other carbon atoms; these indicate a branched chain.

Question 16. The general formula for aldehydes is \( \text{C}_n\text{H}_{2n+1}\text{CHO} \). The value of 'n' for the first member.
(a) 1
(b) 0
(c) 0.5
(d) 1.1
Answer: (b) 0
In simple words: For the first member of the aldehyde series, which is formaldehyde (\( \text{HCHO} \)), there are no carbon atoms in the alkyl group part. This means 'n' in the formula \( \text{C}_n\text{H}_{2n+1}\text{CHO} \) must be 0, as \( \text{C}_0\text{H}_1\text{CHO} \) simplifies to \( \text{HCHO} \).

🎯 Exam Tip: The simplest aldehyde, formaldehyde, has no alkyl group (R=H), so the 'n' in \( \text{C}_n\text{H}_{2n+1} \) corresponds to the number of carbons in the alkyl chain, making n=0 for formaldehyde.

Question 17. An organic compound 'X' has the molecular formula \( \text{C}_3\text{H}_6\text{O}_2 \). It has a pleasant smell but does not turn blue litmus red. It has structural formula
(a) \( \text{H}_5\text{C}_2-\text{C=O}-\text{OH} \)
(b) \( \text{CH}_3-\text{C=O}-\text{OCH}_3 \)
(c) both (a) and (b)
(d) None of the options
Answer: (b) \( \text{CH}_3-\text{C=O}-\text{OCH}_3 \)
In simple words: The compound with molecular formula \( \text{C}_3\text{H}_6\text{O}_2 \), a pleasant smell, and that does not change litmus paper is likely an ester. Option (b) shows methyl acetate (\( \text{CH}_3\text{COOCH}_3 \)), which is an ester that fits these properties. Esters are known for their sweet, fruity smells and are typically neutral, so they don't affect litmus.

🎯 Exam Tip: A pleasant smell often indicates an ester, especially when paired with a neutral pH (no litmus change).

Carbon and its Compounds Very Short Answer Type Questions

Question 1. What is a hydrocarbon?
Answer: A hydrocarbon is a chemical compound that is made up entirely of hydrogen and carbon atoms. These organic compounds form the basis of many fuels and raw materials. Petroleum and natural gas are rich sources of hydrocarbons.
In simple words: Hydrocarbons are compounds only made of hydrogen and carbon.

🎯 Exam Tip: Remember that hydrocarbons are fundamental organic compounds, forming the backbone of much of organic chemistry.

Question 2. Give different forms in which carbon occurs in nature.
Answer: Carbon can be found in nature in both free and combined forms. In its free form, it exists as allotropes like graphite and diamond. In combined forms, carbon is found in compounds such as carbon dioxide in the air and carbonates in minerals.
In simple words: Carbon is found freely as diamond and graphite, and in compounds like carbon dioxide or carbonates.

🎯 Exam Tip: Distinguish between elemental carbon (allotropes) and carbon in compounds when describing its occurrence in nature.

Question 3. Name two types of hydrocarbon.
Answer: The two main types of hydrocarbons are saturated hydrocarbons and unsaturated hydrocarbons. Saturated hydrocarbons contain only single bonds, while unsaturated hydrocarbons contain at least one double or triple bond.
In simple words: The two types of hydrocarbons are saturated (only single bonds) and unsaturated (double or triple bonds).

🎯 Exam Tip: The key difference between saturated and unsaturated hydrocarbons lies in the type of carbon-carbon bonds present (single vs. double/triple).

Question 4. What are covalent bonds?
Answer: Covalent bonds are chemical bonds that are formed when two atoms share a pair of electrons. In covalent compounds, the intermolecular forces between molecules are typically small, which makes these bonds relatively easy to break. This sharing creates a strong link between the atoms themselves.
In simple words: Covalent bonds happen when atoms share electrons. They are usually strong bonds between atoms.

🎯 Exam Tip: Focus on "sharing of electrons" as the core definition of a covalent bond, and note that these bonds are strong within molecules but weaker between molecules.

Question 5. What is catenation?
Answer: Catenation is the unique ability of a carbon atom to form strong bonds with other carbon atoms. This property allows carbon to create long chains, branched structures, and large cyclic molecules. This is why carbon forms so many different compounds.
In simple words: Catenation is carbon's special ability to link up with other carbon atoms to form long chains and big molecules.

🎯 Exam Tip: Catenation is a defining characteristic of carbon that explains the vast diversity of organic compounds.

Question 6. Name two forms of allotropes of carbon.
Answer: Two well-known forms of allotropes of carbon are diamond and graphite. Both are made only of carbon atoms, but their different arrangements give them very different properties.
In simple words: Diamond and graphite are two forms of carbon's allotropes.

🎯 Exam Tip: Allotropes are different structural forms of the same element, showing distinct physical properties but similar chemical behavior.

Question 8. Identify the following compound.
\( \text{H} \)
\( \text{|} \)
\( \text{H}-\text{C}-\text{C=C}-\text{H} \)
\( \text{|} \)
\( \text{H} \)
Answer: Propyne.
In simple words: This compound is called propyne. It has three carbon atoms in a chain and a triple bond between two of them.

🎯 Exam Tip: Compounds with a triple bond are alkynes, and the prefix "prop-" indicates three carbon atoms.

Question 9. Name the following compound.
\( \quad\quad \text{H} \)
\( \quad\quad \text{|} \)
\( \quad \text{H}-\text{C}\text{---}\text{C}-\text{H} \)
\( \quad \text{//}\\ \text{H}-\text{C}\text{---}\text{C}-\text{H} \)
\( \quad\quad \text{|} \)
\( \quad\quad \text{H} \)
Answer: Benzene, \( \text{C}_6\text{H}_6 \).
In simple words: This six-carbon ring structure with alternating single and double bonds is called benzene. It is a very important aromatic compound.

🎯 Exam Tip: Benzene is characterized by its stable hexagonal ring structure with delocalized pi electrons, making it an aromatic compound.

Question 10. Give the formula for the functional group of aldehyde.
Answer: The functional group for an aldehyde is \( \text{-CHO} \). It consists of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydrogen atom, and also connected to the rest of the molecule.
\( \quad \text{O} \)
\( \quad \text{||} \)
\( \text{-C}-\text{H} \)
In simple words: The aldehyde functional group is \( \text{-CHO} \), where a carbon atom is double-bonded to oxygen and single-bonded to hydrogen.

🎯 Exam Tip: Recognise the aldehyde group as \( \text{-CHO} \) or \( -\text{C}(=\text{O})\text{H} \); it's always at the end of a carbon chain.

Question 12. Name the given compound
\( \text{H}\quad\text{H} \)
\( \text{|} \quad \text{|} \)
\( \text{H}-\text{C}-\text{C}-\text{C}-\text{C}-\text{H} \)
\( \text{|} \quad \text{|} \quad \text{|} \quad \text{|} \)
\( \text{H}\quad\text{H}\quad\text{O}\quad\text{H} \)
Answer: 2-Butanone.
In simple words: This compound has four carbon atoms, and the oxygen is double-bonded to the second carbon from the end, making it a ketone called 2-butanone.

🎯 Exam Tip: Ketones are named by replacing the '-e' of the parent alkane with '-one', with a number indicating the position of the carbonyl group if necessary.

Question 13. How can you convert ethene into ethane?
Answer: Ethene can be converted into ethane through a process called hydrogenation. This involves adding hydrogen gas to ethene in the presence of a catalyst, such as nickel or palladium. The double bond in ethene breaks, and hydrogen atoms attach to the carbon atoms, forming a single bond.
In simple words: You can change ethene to ethane by adding hydrogen gas to it, using a special helper chemical called a catalyst.

🎯 Exam Tip: Hydrogenation is a key reaction for converting unsaturated hydrocarbons (alkenes/alkynes) into saturated ones (alkanes).

Question 14. Give two uses of methane gas.
Answer: Methane gas has several important uses.
(i) It is primarily used as a fuel for heating homes, generating electricity, and powering vehicles.
(ii) It is also the main component of biogas and Compressed Natural Gas (CNG), which are sustainable energy sources.
In simple words: Methane is used as a fuel, and it's a big part of natural gas and biogas.

🎯 Exam Tip: Focus on methane's role as a fuel and its presence in important gas mixtures like natural gas and biogas.

Question 15. What is isomerism?
Answer: Isomerism is a property where two or more chemical compounds have the same molecular formula but different structural arrangements of atoms. This difference in structure leads to different physical and chemical properties for each isomer. For instance, both butane and isobutane have the formula \( \text{C}_4\text{H}_{10} \) but are structured differently.
In simple words: Isomerism is when different compounds have the same chemical formula but different structures.

🎯 Exam Tip: Understand that isomers are distinct compounds, despite sharing the same molecular formula, because their atoms are connected differently.

Question 16. Name the second member of alkyne series.
Answer: The alkyne series starts with ethyne (\( \text{C}_2\text{H}_2 \)), which is the first member. Therefore, the second member of the alkyne series is propyne (\( \text{C}_3\text{H}_4 \)). Each successive member in a homologous series adds a \( \text{CH}_2 \) unit.
In simple words: The second compound in the alkyne family, after ethyne, is propyne.

🎯 Exam Tip: Recall the general formula for alkynes (\( \text{C}_n\text{H}_{2n-2} \)) and the prefixes for carbon chain lengths (eth-, prop-, but-, etc.).

Question 18. Give the IUPAC name of acetic acid and propyl alcohol.
Answer: The IUPAC name for acetic acid is ethanoic acid. The IUPAC name for propyl alcohol is propanol. These systematic names help avoid confusion as common names can sometimes vary.
In simple words: Acetic acid is also called ethanoic acid, and propyl alcohol is called propanol in IUPAC naming.

🎯 Exam Tip: Always use IUPAC nomenclature for clarity; common names can be ambiguous or vary regionally.

Question 19. What will happen to the litmus solution in carboxylic acid?
Answer: When litmus solution is added to a carboxylic acid, the blue litmus paper will change to red. However, red litmus paper will remain the same and show no change. This indicates that carboxylic acids are acidic in nature.
In simple words: In a carboxylic acid, blue litmus paper turns red, but red litmus paper stays red.

🎯 Exam Tip: Remember that acids turn blue litmus red, while bases turn red litmus blue. No change means the litmus paper already matches the solution's pH indicator.

Question 20. Give the electron dot structure of \( \text{CH}_3\text{Cl} \) and \( \text{C}_2\text{H}_2 \).
Answer:
Electron dot structure of \( \text{CH}_3\text{Cl} \):
\( \quad\quad \text{H} \)
\( \quad\quad \text{|} \)
\( \text{H}-\text{C}-\text{Cl} \)
\( \quad\quad \text{|} \)
\( \quad\quad \text{H} \)
Electron dot structure of \( \text{C}_2\text{H}_2 \) (Ethyne):
\( \text{H}-\text{C}\text{≡}\text{C}-\text{H} \)
In simple words: The electron dot structures show how electrons are shared between atoms to form bonds. For \( \text{CH}_3\text{Cl} \), carbon shares electrons with three hydrogens and one chlorine. For \( \text{C}_2\text{H}_2 \), the two carbon atoms share three pairs of electrons, forming a triple bond, and each carbon shares one pair with a hydrogen atom.

🎯 Exam Tip: When drawing electron dot structures, ensure that each atom achieves a stable octet (or duet for hydrogen) by sharing electrons, and use dots or crosses to represent valence electrons.

Question 21. Draw the electron dot structure of \( \text{N}_2 \) and \( \text{NH}_3 \).
Answer:
Electron dot structure of \( \text{N}_2 \):
\( \text{N}\text{≡}\text{N} \)
Electron dot structure of \( \text{NH}_3 \) (Ammonia):
\( \quad\quad\quad \text{H} \)
\( \quad\quad\quad \text{|} \)
\( \text{H}-\text{N}-\text{H} \)
In simple words: For \( \text{N}_2 \), the two nitrogen atoms share three pairs of electrons, forming a strong triple bond. For \( \text{NH}_3 \), the nitrogen atom shares one pair of electrons with each of the three hydrogen atoms, and it also has one lone pair of electrons.

🎯 Exam Tip: Remember that nitrogen atoms need three bonds to achieve a stable octet, so they form a triple bond in \( \text{N}_2 \) and three single bonds (with one lone pair) in \( \text{NH}_3 \).

Question 23. Give the IUPAC name and write the functional group present in vinegar.
Answer: The IUPAC name for vinegar is ethanoic acid. The functional group present in ethanoic acid (and thus in vinegar) is the carboxyl group, which is written as \( \text{-COOH} \). This group consists of a carbonyl group (\( \text{C=O} \)) and a hydroxyl group (\( \text{-OH} \)) attached to the same carbon.
In simple words: Vinegar's IUPAC name is ethanoic acid, and its main functional part is the carboxyl group (\( \text{-COOH} \)).

🎯 Exam Tip: The carboxyl group (\( \text{-COOH} \)) is characteristic of carboxylic acids and is responsible for their acidic properties.

Question 24. A compound has a molecular formula \( \text{C}_2\text{H}_6\text{O} \). It is used as a fuel. Name the compound and name its functional group.
Answer: The compound with the molecular formula \( \text{C}_2\text{H}_6\text{O} \) that is used as a fuel is ethanol. Its chemical formula can also be written as \( \text{C}_2\text{H}_5\text{OH} \). The functional group present in ethanol is the hydroxyl group, which is represented as \( \text{-OH} \). This group is characteristic of alcohols.
In simple words: The compound is ethanol, and its functional group is the hydroxyl group (\( \text{-OH} \)).

🎯 Exam Tip: Recognize the \( \text{-OH} \) functional group as indicative of an alcohol, and ethanol as a common fuel and solvent.

Carbon and its Compounds Short Answer Type Questions

Question 1. What is the reactive site in the given hydrocarbon? Write its IUPAC name.
\( \text{H}_3\text{C}-\text{CH}_2-\text{CH} = \text{CH}-\text{CH}_3 \)
Answer: In the hydrocarbon \( \text{H}_3\text{C}-\text{CH}_2-\text{CH} = \text{CH}-\text{CH}_3 \), the reactive site is the double bond. This double bond makes the molecule unsaturated and more prone to chemical reactions. The IUPAC name of the compound is 2-pentene because it has five carbon atoms (pent-), a double bond (-ene), and the double bond starts at the second carbon.
In simple words: The double bond between the carbon atoms is the reactive part. The name of this chemical is 2-pentene.

🎯 Exam Tip: Double and triple bonds are typically the most reactive sites in hydrocarbons, as they allow for addition reactions.

Question 2. What is the difference in the number of carbon and hydrogen atoms between two successive members of a homologous series? Also give the difference in their atomic masses.
Answer: Between two consecutive members of a homologous series, the difference in the number of atoms is one carbon atom and two hydrogen atoms, which corresponds to a \( \text{-CH}_2 \) group. The difference in their atomic masses is therefore 14 atomic mass units (a.m.u.), as carbon has an atomic mass of 12 and two hydrogens contribute 2.
In simple words: Each new member in a homologous series adds one carbon and two hydrogen atoms (\( \text{CH}_2 \)) to the molecule. This means their mass changes by 14 a.m.u. each time.

🎯 Exam Tip: The constant \( \text{CH}_2 \) difference in composition and 14 a.m.u. difference in mass are defining characteristics of a homologous series.

Question 3. Why does carbon form compounds mainly by covalent bonding?
Answer: Carbon forms compounds mainly through covalent bonding due to its small size and tetravalency. To achieve a stable noble gas configuration, carbon needs to gain or lose four electrons. Losing four electrons would require a very high amount of energy, and gaining four electrons would create too much electron-electron repulsion due to its small size. Therefore, sharing electrons through covalent bonds is the most favorable and stable way for carbon to form compounds.
In simple words: Carbon forms bonds by sharing electrons because it is too hard to gain or lose four electrons due to its size and electron arrangement. Sharing is easier.

🎯 Exam Tip: Carbon's tetravalency (ability to form four bonds) and its tendency to share electrons rather than gain or lose them are crucial for covalent bonding.

Question 5. Write the structural formula for bromopentane and ethanoic acid.
Answer:
Structural formula for Bromopentane (\( \text{C}_5\text{H}_{11}\text{Br} \)):
\( \text{H}\quad\text{H}\quad\text{H}\quad\text{H}\quad\text{H} \)
\( \text{|} \quad \text{|} \quad \text{|} \quad \text{|} \quad \text{|} \)
\( \text{H}-\text{C}-\text{C}-\text{C}-\text{C}-\text{C}-\text{Br} \)
\( \text{|} \quad \text{|} \quad \text{|} \quad \text{|} \quad \text{|} \)
\( \text{H}\quad\text{H}\quad\text{H}\quad\text{H}\quad\text{H} \)
Structural formula for Ethanoic acid (\( \text{CH}_3\text{COOH} \)):
\( \quad\quad \text{H}\quad\quad\text{O} \)
\( \quad\quad \text{|} \quad\quad \text{||} \)
\( \text{H}-\text{C}-\text{C}-\text{O}-\text{H} \)
\( \quad\quad \text{|} \)
\( \quad\quad \text{H} \)
In simple words: Bromopentane is a straight chain of five carbons with a bromine atom attached at one end. Ethanoic acid has two carbon atoms; one is part of a methyl group, and the other is part of a carboxyl group.

🎯 Exam Tip: Always ensure all valencies are satisfied (carbon with four bonds, hydrogen with one, oxygen with two, bromine with one) when drawing structural formulas.

Question 6. Draw the structures of two isomers of butane.
Answer: Butane (\( \text{C}_4\text{H}_{10} \)) has two isomers: n-butane and isobutane (or 2-methylpropane).
Structure of n-butane:
\( \text{H}\quad\text{H}\quad\text{H}\quad\text{H} \)
\( \text{|} \quad \text{|} \quad \text{|} \quad \text{|} \)
\( \text{H}-\text{C}-\text{C}-\text{C}-\text{C}-\text{H} \)
\( \text{|} \quad \text{|} \quad \text{|} \quad \text{|} \)
\( \text{H}\quad\text{H}\quad\text{H}\quad\text{H} \)
Structure of isobutane (2-methylpropane):
\( \quad\quad \text{H} \)
\( \quad\quad \text{|} \)
\( \text{H}-\text{C}-\text{H} \)
\( \quad\quad \text{|} \)
\( \text{H}-\text{C}-\text{C}-\text{H} \)
\( \text{|} \quad \text{|} \quad \text{|} \)
\( \text{H}\quad\text{H}\quad\text{H} \)
In simple words: Butane can exist in two forms: a straight chain called n-butane, and a branched chain called isobutane. Both have the same number of carbon and hydrogen atoms but are arranged differently.

🎯 Exam Tip: Isomers have the same molecular formula but different structural formulas; for alkanes, this often involves straight versus branched chains.

Question 7. A student burns a hydrocarbon in air and obtains sooty flame. Give two reasons for this observation.
Answer: A sooty (yellow, smoky) flame is usually observed when there is incomplete combustion of a hydrocarbon. This can happen due to two main reasons:
1. Incomplete combustion of saturated hydrocarbons: If there is not enough oxygen available for saturated hydrocarbons to burn completely, they will produce a sooty flame along with carbon monoxide and soot.
2. Combustion of unsaturated hydrocarbons: Unsaturated hydrocarbons (like alkenes and alkynes) typically have a higher carbon-to-hydrogen ratio. They generally burn with a sooty flame even in a good supply of air because their carbon atoms do not get fully oxidized.
In simple words: A sooty flame happens when a fuel doesn't burn completely, either because there isn't enough oxygen or because the fuel itself (like unsaturated hydrocarbons) naturally produces more soot.

🎯 Exam Tip: Sooty flames indicate incomplete combustion, which can be caused by insufficient oxygen or the presence of unsaturated hydrocarbons.

Question 8. Differentiate between saturated and unsaturated hydrocarbons. Give one example for each.
Answer:

In simple words: Saturated hydrocarbons have only single bonds and burn cleanly, while unsaturated ones have double or triple bonds and often burn with a smoky flame.

🎯 Exam Tip: The presence of single versus multiple bonds is the fundamental distinguishing feature, impacting flame type and typical reaction pathways.

Question 9. Write the general formula for each of the following hydrocarbons and give one example for each.
(i) Alkene
(ii) Alkyne
Answer:
(i) Alkene: The general formula for alkenes is \( \text{C}_n\text{H}_{2n} \). An example of an alkene is ethene (\( \text{C}_2\text{H}_4 \)). Alkenes contain at least one carbon-carbon double bond.
(ii) Alkyne: The general formula for alkynes is \( \text{C}_n\text{H}_{2n-2} \). An example of an alkyne is ethyne (\( \text{C}_2\text{H}_2 \)). Alkynes contain at least one carbon-carbon triple bond.
In simple words: Alkenes have the formula \( \text{C}_n\text{H}_{2n} \) (like ethene), and alkynes have \( \text{C}_n\text{H}_{2n-2} \) (like ethyne).

🎯 Exam Tip: Memorize the general formulas for alkanes, alkenes, and alkynes, as they are essential for identifying and naming hydrocarbons.

Question 10. Diamond and graphite show different physical properties although they are made up of carbon and shows same chemical properties. What is this property called?
Answer: This property is called allotropy. The physical properties of diamond and graphite are different because the way carbon atoms are bonded and arranged within their structures varies. In diamond, each carbon atom is strongly bonded to four other carbon atoms in a tetrahedral arrangement, making it very hard. In contrast, graphite consists of carbon atoms bonded to three other carbon atoms in hexagonal sheets, which are weakly bonded to each other and can slide past each other, making graphite soft.
In simple words: When an element exists in different forms with different physical properties but the same chemical properties, it's called allotropy. Diamond and graphite are examples of carbon's allotropes.

🎯 Exam Tip: Allotropy is about different structural arrangements of atoms of the same element, leading to distinct physical properties while chemical behavior remains similar.

Carbon and its Compounds Long Answer Type Questions

Question 1. (a) What do you mean by allotropy?
(b) What is isomerism?
(c) Give one example of homologous series, give two properties of it.
(d) What is the full form of IUPAC?
Answer:
(a) Allotropy: Allotropy is the property of an element to exist in different physical forms while having the same chemical properties. This difference arises from the distinct ways atoms are bonded to each other. For example, diamond and graphite are both made of pure carbon but look and feel very different due to their atomic structures.

(b) Isomerism: Isomerism is a phenomenon where two or more chemical compounds have the exact same molecular formula but possess different structural arrangements of atoms. These structural differences lead to variations in their physical and chemical properties. A good example is butane and isobutane, both \( \text{C}_4\text{H}_{10} \), but one is a straight chain and the other is branched.
(c) Homologous series: A homologous series is a family of organic compounds that follow a general formula and have similar chemical properties, with successive members differing by a \( \text{-CH}_2 \) group. An example is the alkane series: Methane (\( \text{CH}_4 \)), Ethane (\( \text{C}_2\text{H}_6 \)), Propane (\( \text{C}_3\text{H}_8 \)), Butane (\( \text{C}_4\text{H}_{10} \)), etc.
Two properties of a homologous series are:
1. The difference between any two consecutive members in the series is a \( \text{-CH}_2 \) group, resulting in a mass difference of 14 a.m.u.
2. All members in a given homologous series show similar chemical properties due to the presence of the same functional group, but there is a gradual change in their physical properties as molecular mass increases.
(d) IUPAC: The full form of IUPAC is the International Union of Pure and Applied Chemistry. This organization is responsible for setting global standards for chemical nomenclature and terminology.
In simple words: Allotropy is when an element like carbon appears in different forms (like diamond and graphite). Isomerism is when different chemicals have the same formula but different structures. A homologous series is a group of chemicals that follow a pattern, like alkanes, each one bigger by a \( \text{CH}_2 \) unit, and they act alike. IUPAC is the group that sets the rules for naming chemicals.

🎯 Exam Tip: For definitions, provide clear, concise explanations and use examples where appropriate to illustrate the concept fully.

Question 2. (a) What are hydrocarbons?
(b) Give difference between saturated and unsaturated hydrocarbons.
(c) Why does carbon form large number of compounds?
Answer:
(a) Hydrocarbons: Hydrocarbons are organic chemical compounds that are exclusively composed of hydrogen and carbon atoms. They are fundamental to organic chemistry and serve as primary components of fossil fuels like petroleum and natural gas.
(b) Difference between saturated and unsaturated hydrocarbons:

(c) Carbon forms a large number of compounds due to three main properties:
1. Catenation: This is carbon's unique ability to form strong covalent bonds with other carbon atoms, creating long straight chains, branched chains, and stable cyclic structures.
2. Isomerism: Carbon compounds can exist in multiple structural forms (isomers) even with the same molecular formula, leading to a wider variety of distinct compounds.
3. Tetravalency: Carbon has a valency of four, meaning each carbon atom can form four covalent bonds with other carbon atoms or other elements like hydrogen, oxygen, and nitrogen. This allows for diverse bonding patterns and the creation of complex molecules.
In simple words: (a) Hydrocarbons are compounds made only of carbon and hydrogen. (b) Saturated ones have only single bonds, while unsaturated ones have double or triple bonds. (c) Carbon makes many compounds because it can link with other carbon atoms in long chains, form different shapes (isomers), and make four bonds with other atoms.

🎯 Exam Tip: When explaining why carbon forms many compounds, emphasize catenation, isomerism, and tetravalency as the key contributing factors.

Question 3. Give a brief overview of different systems of nomenclature of organic compounds.
Answer: Organic compounds can be named using three main systems:
1. Trivial System: This is an older system where compounds are named based on their natural source or properties. For example, \( \text{CH}_3\text{OH} \) is called "wood spirit" because it was first obtained from wood. Acetic acid (from vinegar) is another example. While simple for common compounds, it lacks systematic rules for complex molecules.
2. Derived System: In this system, compounds are named as derivatives of simpler parent compounds. For instance, \( \text{CH}_3\text{CH}_2\text{OH} \) (ethanol) might be named as "methyl carbinol", where carbinol (\( \text{CH}_3\text{OH} \)) is the parent compound. This system can become cumbersome for larger or more complex structures.
3. IUPAC System (International Union of Pure and Applied Chemistry): This is the most widely accepted and systematic naming system. It uses a set of rules to ensure each compound has a unique and unambiguous name. The rules involve:
• Identifying the longest continuous carbon chain (parent chain).
• Numbering the carbon chain to give substituents and functional groups the lowest possible numbers.
• Using prefixes for the number of carbon atoms (e.g., meth-, eth-, prop-).
• Using suffixes to indicate the type of bond (e.g., -ane, -ene, -yne) and functional groups (e.g., -ol for alcohol, -oic acid for carboxylic acid).
• Writing the name by combining prefixes, parent chain name, and suffix in a specific order.
In simple words: There are three main ways to name organic chemicals: the Trivial System (old names from where they came from), the Derived System (names based on simpler chemicals), and the IUPAC System (a modern, rule-based way that gives each chemical a unique name).

🎯 Exam Tip: Understand that the IUPAC system is the most important for systematic naming, while trivial and derived names offer historical context but are less precise for new or complex compounds.

Question 4. Write a short note on CNG and differentiate between CNG and LPG.
Answer: Compressed Natural Gas (CNG) is essentially natural gas that has been highly pressurized. This gas is typically found above oil layers in underground wells. When CNG is burned, it produces very small amounts of carbon monoxide or carbon dioxide due to its lower carbon content. This makes CNG a more environmentally friendly fuel compared to traditional petroleum products, contributing less to air pollution.

In simple words: CNG is natural gas pressed into a small space that burns cleanly, causing less pollution. LPG is a heavier gas from crude oil used for cooking, while CNG is a lighter gas from wells used in cars.

🎯 Exam Tip: When comparing fuels like CNG and LPG, always highlight key differences in their source, density, safety, and main uses to score full marks.

Question 5. What is nylon-66? Give the reaction of production of nylon. Write some uses of nylon.
Answer: Nylon-66 is a type of synthetic polymer. It is created when two specific molecules, adipic acid (which has six carbon atoms) and hexamethylenediamine (also with six carbon atoms), join together in a special reaction called condensation polymerization. The name 'Nylon-66' comes from both starting materials having six carbon atoms. This type of reaction, where small molecules join and release a smaller molecule like water, is known as condensation polymerization.
The production reaction is:
\( n HOOC-(CH_2)_4-COOH \text{ (Adipic acid)} + n H_2N-(CH_2)_6-NH_2 \text{ (Hexamethylenediamine)} \)
\( \implies \) \( [-OC-(CH_2)_4-CO-NH-(CH_2)_6-NH-]_n \text{ (Nylon-66)} + 2n H_2O \)
Nylon-66 is used in many things like making gears and bearings for machines. It is also found in tyres, various types of cloth, fibres, ropes, and even toothbrushes. Its strength and durability make it suitable for these diverse applications.
In simple words: Nylon-66 is a man-made material formed by linking two different chemicals, each having six carbon atoms. It is used to make strong products like machine parts, tyres, and ropes.

🎯 Exam Tip: Remember that Nylon-66 is a condensation polymer, meaning water is removed during its formation. Also, note that the '66' in its name refers to the six carbon atoms in each of its monomer units.

Question 38. Write short notes on following:
(a) Freon
(b) CNG
(c) Natural rubber
Answer:
(a) Freon: Freons are a group of chemical compounds known as chlorofluorocarbons (CFCs). They are created when carbon atoms bond with both chlorine and fluorine atoms. For example, Freon-11 is produced when carbon tetrachloride reacts with hydrogen fluoride, especially with antimony pentachloride acting as a catalyst. These compounds were widely used as refrigerants and propellants, but their use has been greatly reduced because they are known to damage the Earth's ozone layer.
In simple words: Freons are chemicals made of carbon, chlorine, and fluorine. They were used in refrigerators but are now avoided because they harm the ozone layer.

(b) CNG: Compressed Natural Gas (CNG) is natural gas that has been compressed under high pressure. This gas is found above oil layers in oil wells. When CNG burns, it produces very small amounts of carbon monoxide or carbon dioxide because it contains less carbon than other fuels. This characteristic makes CNG a more environment-friendly fuel choice compared to other petroleum-based products.
In simple words: CNG is natural gas pressed into a small space. It burns cleanly and causes less air pollution.

(c) Natural rubber: Natural rubber is a polymer obtained from latex, which is a milky sap collected from rubber trees. It is essentially a polymer of a molecule called isoprene. To process it, acetic acid is added to the latex, causing it to solidify. The initial rubber produced this way is highly elastic but lacks sufficient tensile strength for many applications. To enhance its strength, durability, and reduce its elasticity, it undergoes a process called vulcanization, where it is heated with sulphur. Vulcanization prevents the rubber from becoming sticky in warm weather and brittle in cold weather.
In simple words: Natural rubber comes from tree sap. It is made stronger and more useful by heating it with sulphur in a process called vulcanization.

🎯 Exam Tip: For short notes, always define the term, explain its composition or origin, mention its key properties or uses, and include any significant environmental or historical context if relevant.