Selina Concise Solutions for ICSE Class 8 Chemistry Chapter 9 Carbon and Its Compounds

Points to Remember:

1. Carbon occurs in the earth’s crust in the free as well as in the combined state.
2. In the free state, it occurs as coal, diamond and graphite.
3. In the combined state, carbon occurs in atmosphere (CO₂) natural gas, food nutrients and carbonates.
4. Diamond is the hardest naturally occuring substance known.
5. Fullerenes are discovered only recently.
 
Carbon is a versatile element that forms the basis of all life on Earth. It can be found alone as a mineral or joined with other elements to form complex substances like the air we breathe and the food we eat.
Teacher's Tip: Think of "Free state" as carbon being "Single" (like Diamond) and "Combined state" as carbon being "Married" to other atoms (like in CO₂).
Exam Tip: Remember that Diamond, Graphite, and Coal are all made of the same element - Carbon.

Exercise - I

Question 1: Fill in the blanks.
(a) Carbon is present in both living and non-living things.
(b) The tendency of an element to exist in two or more forms but in the same physical state is called Allotropy.
(c) Crystalline and non-crystalline are the two major crystalline allotropes of carbon.
(d) Diamond is the hardest substance that occurs naturally.
(e) The name ‘carbon’ is derived from the Latin word carbo.
 
This exercise helps you identify the presence of carbon in the world around you. Allotropy is a special property where the same element can look and feel very different, like soft graphite and hard diamond.
Teacher's Tip: The word 'carbo' actually means 'charcoal' in Latin.
Exam Tip: Spelling is important for terms like "Allotropy" and "Crystalline" to score full marks.

Question 2: Choose the correct alternative.

(a) In combined state, carbon occurs as
(i) coal
(ii) diamond
(iii) graphite
(iv) petroleum
Answer: petroleum

(b) A crystalline form of carbon is
(i) lampblack
(ii) gas carbon
(iii) sugar
(iv) fullerene
Answer: fullerene
 
In the combined state, carbon is mixed with other elements like hydrogen in petroleum. Crystalline forms have atoms arranged in a regular, repeating pattern, whereas amorphous forms do not.
Teacher's Tip: Remember that "Sugar" is a compound containing carbon, not an allotrope of carbon itself.
Exam Tip: Read all options carefully; fullerenes are the third crystalline allotrope discovered after diamond and graphite.

Question 4: Define the following terms:
(a) Allotropy
(b) Carat
(c) Crystal
(d) Catenation
Answer:
(a) Allotropy: Allotropy is defined as the phenomenon due to which an element exists in two or more forms in the same physical state with identical chemical properties but with different physical properties.
(b) Carat - The weight of diamond is expressed in carats [ 1 carat = 0.2 g]
(c) Crystal - A crystal is a homogeneous solid which particles (atoms, molecules or ions) are arranged in difinite pattern due to which they have definite geometrical shape with plane surfaces e.g. sugar and sodium chloride.
(d) Catenation - The large number of organic compounds is due to the ability of carbon atom to form long chains with other carbon atoms through the sharing of electrons. This unique property of carbon is known as catenation.
 
Allotropy allows carbon to be both the softest and hardest material. Catenation is the reason there are millions of different carbon-based chemicals in the world.
Teacher's Tip: Think of Catenation as carbon atoms holding hands to form long human chains.
Exam Tip: For "Carat," always include the specific weight conversion (1 carat = 0.2 g) for a perfect answer.

Question 5: State the terms:

(a) Substances whose atoms or molecules are arranged in a definite pattern. 
Answer: Crystals.

(b) Different forms of an element found in the same physical state. 
Answer: Allotropy.

(c) The property by which atoms of an element link together to form long chain or ring compounds. 
Answer: Catenation
 
Identifying these terms helps you understand the structural organization of matter. These properties define how carbon atoms interact to build complex structures.
Teacher's Tip: If the atoms have a pattern, it's a "Crystal"; if they "link together," it's "Catenation."
Exam Tip: Be precise with terminology; "allotropy" refers to the phenomenon, while "allotropes" refers to the forms themselves.

Question 6: Name the following:

(a) The hardest naturally occurring substance. 
Answer: Diamond.

(b) A greyish black non-metal that is a good conductor of electricity. 
Answer: Graphite.

(c) The third crystalline form of carbon. 
Answer: Fullerenes.
 
Diamond and graphite are both pure carbon but behave differently due to their atom arrangement. Fullerenes are a newer discovery shaped like soccer balls.
Teacher's Tip: Graphite is the only non-metal you use every day (in your pencil) that can conduct electricity.
Exam Tip: When naming substances, use the correct scientific spelling for "Fullerenes."

Question 7: Answer the following questions:
(a) Why is graphite a good conductor of electricity but not diamond?
(b) Why is diamond very hard?
(c) What are fullerenes? Name the most common fullerenes.
(d) What impurity is present in black diamond?
(e) Explain the softness of graphite with reference to its structure.
Answer: 
(a) In a graphite molecule, one valence electron of each carbon atom remains free, Thus making graphite a good conductor of electricity. Whereas in diamond, they have no free mobile electron. Thats why diamond are bad conductor electricity.
(b) A diamond is a giant molecule. The number of valence electrons in carbon atom is four. As such each carbon atom is linked with four neighboring carbon atoms. Thus forming a rigid tetrahedral structure. It is the strong bonding’that makes diamond the hardest substance.
(c) Fullerenes: Fullerenes are the third crystalline form of carbon. Though they were discovered only recently. They have.been found to exist in interstellar dust as well as in the geological formations of the earth. Common fullerenes are C - 32, C - 50, C - 70 and C - 76
(d) Black diamonds have copper oxide present in them as impurity.
(e) In a graphite molecule of each carbon atoms is linked with three neighboring carbon atoms. Thus forming a hexagonal arrangement of atoms. These hexagonal grouping of carbon atoms are arranged as layers or sheets piled one the top of other. The layers are held together by weak forces such that they can slide over one another. That is why graphite is soft. 
The way carbon atoms are "linked" determines if the material is hard like diamond or soft like graphite. Electricity can only flow if there are "free" electrons moving around, which is why graphite conducts and diamond doesn't.
Teacher's Tip: Visualize diamond as a 3D cage and graphite as a stack of slippery papers.
Exam Tip: Use the word "tetrahedral" for diamond and "hexagonal layers" for graphite to get full marks.

Question 8: Give two uses of (a) graphite (b) diamond.
Answer:
(a) Uses of graphite:
1. For making the electrodes of electric furnaces.
2. For making crucibles for melting metals due to its high melting points.
(b) Uses of Diamond:
1. Diamond is used in jewellery as a gem
2. It is used for cutting and drilling rocks, glass,
 
Graphite is used where heat and electricity are needed, while diamond is valued for its beauty and extreme strength. These uses directly relate to the physical properties discussed in previous sections.
Teacher's Tip: Think of graphite as a "heat-proof" material and diamond as a "super-cutter."
Exam Tip: Always number your points when asked for "two uses" to make your answer easy for the teacher to read.

Question 9: Write three differences between graphite and diamond.
Answer:  Difference between diamond and graphite.
Diamond
1. Pure diamond is colourless and transparent.
2. It is the hardest naturally occurring substance.
3. It has high density i.e. 3.5 gcm³
4. It is bad conduct of electricity.
5. It bums in air at 900°C to form carbon dioxide.
Graphite
1. Graphite is greyish black opaque and shiny.
2. It is soft and greasy to touch.
3. It has low density i.e. 2.39 g cm³
4. It is good conductor of electricity.
5. It bums in air at 700°C to form carbon dioxide.
 
This comparison shows how the same element, Carbon, can vary in color, density, and strength. Notice that even their burning temperatures are different based on their structure.
Teacher's Tip: Remember that "D" is for Diamond and "Dense" (it has higher density than graphite).
Exam Tip: Presenting differences in a clear, numbered format for both substances is a great way to ensure full marks.

Exercise - II

Question 1: Fill in the blanks:
(a) Charcoal is formed when wood is burnt in a limited supply of air.
(b) Coal is a amorphous form of carbon.
(c) Peat is the most inferior form of coal.
(d) Wood charcoal is a bad conductor of heat and electricity.
(e) lampblack is used in making black shoe polish.
 
Amorphous forms of carbon like charcoal and coal don't have a neat crystal structure. This exercise highlights how different processes like burning in limited air create useful products like lampblack.
Teacher's Tip: "Amorphous" simply means "without a shape" or pattern at the atomic level.
Exam Tip: Don't confuse "Peat" (inferior coal) with "Anthracite" (best coal).

Question 2: Choose the correct alternative

(a) Anthracite is
(i) an inferior type of coal
(ii) a superior type of coal
(iii) a cheapest form of coal
(iv) none of above
Answer: a superior type of coal

(b) Destructive distillation of coal yields
(i) coal tar
(ii) coal gas
(iii) coke
(iv) all of the above
Answer: all of the above

(c) Lamp black is
(i) an amorphous form of carbon
(ii) a crystalline form of carbon
(iii) a pure form of carbon
(iv) a cluster of carbon atoms
Answer: an amorphous form of carbon

(d) The process by which decayed plants slowly convert into coal is called.
(i) petrification
(ii) carbonisation
(iii) carbonification
(iv) fermentation
Answer: carbonisation

(e) The purest form of the amorphous carbon is
(i) wood charcoal
(ii) sugar charcoal
(iii) bone charcoal
(iv) lampblack
Answer: sugar charcoal
 
Anthracite is the best coal because it has the most carbon and burns the cleanest. Destructive distillation is a way of breaking down coal to get other useful fuels and materials.
Teacher's Tip: Remember: "A" is for Anthracite and "A" is for "A+ grade" coal!
Exam Tip: If you see a question about "decayed plants," the answer is almost always carbonisation.

Question 3: Write ‘true’ or ‘false’ against the following statements:

(a) Charcoal is a good adsorbent.
Answer: True

(b) Coke is obtained by destructive distillation of sugar.
Answer: False

(c) Activated charcoal is a good conductor of electricity.
Answer: False

(d) Wood charcoal is an important constituent of gun powder.
Answer: True

(e) Coal gas is used in the preparation of artificial ferilizers.
Answer: False.
 
Charcoal's ability to "adsorb" means it can trap gases and impurities on its surface. This property makes it very useful for cleaning air and water.
Teacher's Tip: "Adsorb" (with a 'd') means sticking to the surface, while "Absorb" (with a 'b') means soaking into the middle.
Exam Tip: When you see "Coke" and "Sugar," remember that coke comes from coal, not sugar.

Question 4: Define the following:
(a) Carbonization (b) Adsorption (c) Bone black
Answer:
(a) Carbonization: The process of the slow conversion of vegetable matter into carbon rich substances is called carbonization.
(b) Adsorption: Adsorption is the property due to which a substance absorbs gases, liquids and solids on its surface.
(c) Bone black: The Carbon content of bone charcoal is separated by treating the latter with hydrchloride acid, which dissolves the calcium phosphate. Carbon is then filtered out of the solution and in this form it is called bone black. 
Carbonization is a natural process that takes millions of years to create coal. Adsorption is a physical property used in filters to catch tiny particles.
Teacher's Tip: Think of "Bone black" as the dark carbon left over after bones are cleaned with acid.
Exam Tip: For "Adsorption," emphasize that it happens on the "surface" to get the definition right.

Question 5: Name the following:
(a) Substances whose atoms or molecules are not arranged in a geometrical pattern. - Amorphous
(b) The best variety of coal. - Bituminous
(c) The purest form of amorphous carbon. - Anthracite
(d) An amorphous form of carbon that contains about 98% carbon. - Anthracite
(e) Mixture of carbon monoxide and hydrogen. - Water gas. 
Note that Anthracite is considered both the purest coal and a very pure form of amorphous carbon. Water gas is an important industrial fuel made from carbon and steam.
Teacher's Tip: Although Bituminous is a "best" variety for common use, Anthracite is the "purest."
Exam Tip: Use the name "Water gas" specifically for the CO + H₂ mixture.

Question 7: Answer the following questions:
(a) What is destructive distillation? What are the products formed due to the destructive distillation of coal?
(b) Why is wood charcoal used in water filters and gas masks?
(c) How is wood charcoal made locally? What other substances are formed in the process.
(d) How many carbon atoms are there in Buckminster fullerenes?
Answer:
(a) Destructive Distillation: When a substances is heated in the absence of air. The process is called destructive distillation. Products formed are: Coke, Coal tar, Coal gas and ammonia solution
(b) Due to its high adsorbing capacity, wood charcoal is used as gas masks to adsorb harmful gases. Wood charcoal is porous, that is why it is used to filter water.
(c) Wood charcoal is prepared when wood is heated in a limited supply of air. Locally wood charcoal is prepared by piling logs of wood one above the other with a gap in the centre of the pile. The pile is covered with wet clay to prevent the entry of air. A few holes are left at the bottom of the pile. The wood is set on fire. After some time when fire dies out, wood charcoal is left behind. The other substances are - wood tar, pyroligneous acid and wood gas.
(d) 60 carbon atoms are arranged in spherical structure in Buckminster fullerenes. 
Heating in the absence of air (destructive distillation) forces a chemical change without burning everything away. This is how we produce coke and charcoal from natural materials like coal and wood.
Teacher's Tip: Think of the local charcoal pile as a big earthen oven that "bakes" the wood into carbon.
Exam Tip: For Buckminster fullerenes, always write "C60" or "60 carbon atoms" for the correct count.

Question 7:
(a) Descirbe the formation of coal,
(b) Name four types of coal with percentage of carbon present in each, with uses.
Answer:
(a) Formation of coal:- The formation of coal took millions of years. Coal was formed by the bacterial decomposition of ancient vegetable matter hurried under successive layers of the earth. Under in action of high temperature and pressure, and in the abcence of air, the decayed vegetable matter converted into coal.
(b) Types of Coal:
1. Peat: It is light brown in colour and contains only 50 - 60% carbon. It is the most inferior form of coal.
2. Lignite: it contains more than 60% carbon. It is brown in colour and harder than peat.
3. Bituminous: It has 90%, 80%, 70 - 75% carbon contents. Bituminous coal is the most common variety of coal and used as house hold coal.
4. Anthracite: It is the purest variety of coal. Its carbon contents vary between 92 - 98%. It is hard, dense and black, difficultto ignite.
Uses of coal:
1. Coal is used as both domestic and industrial fuel.
2. It is used to prepare coke, coal gas and coal tar. 
Coal is essentially solar energy from prehistoric plants trapped in rock. The quality of coal depends on how long it was buried and how much pressure it endured.
Teacher's Tip: Use the order P-L-B-A (Peat, Lignite, Bituminous, Anthracite) to remember the rank from lowest to highest carbon.
Exam Tip: Be sure to include the carbon percentages for each type to demonstrate your thorough knowledge.

Question 9: Name the products formed when:
(a) wood is burnt in the absence of air.
(b) bone is heated in the absence of air.
(c) diamond is burnt in air at 900°C.
(d) graphite is subjected to high pressure and 3000°C temperature.
Answer:
(a) Wood charcoal is formed when wood is burnt in limited supply of air.
(b) Bone charcaol, bone oil and organic compound pyridine.
(c) Carbon dioxide.
(d) Artificial diamond. 
Heating different carbon sources in specific ways yields different products, from common fuels to high-tech artificial gems. Note that even the "king of gems" turns back into invisible CO₂ gas if you heat it enough.
Teacher's Tip: "In the absence of air" is the key phrase for making charcoal rather than just ash.
Exam Tip: For graphite under high pressure, use the term "Artificial diamond" to be specific.

Question 9: Give two uses for each of the following:
(a) coal (b) coke (c) wood charcoal (d) sugar charcoal (e) bone charcoal (f) lampblack
Answer:
(a) Uses of coal

• It is used as both domestic and industrial fuel.
• It is used to prepare coke, coal gas and coal tar.

(b) Uses of coke

• Coke is used as a smokeless fuel, in smelting furnaces.
• It is used in the manufacturing of water and producer gas.

(c) Uses of wood charcoal:

• Wood charcoal is used as a fuel.
• It is an important constituent of gun powder.

(d) Sugar charcoal:

• Sugar charcoal is mostly used as a reducing agent.
• It is used to decolourise coloured solutions.

(e) Bone charcoal:

• It is extensively used to decolourise cane-sugar in the process of manufacturing sugar.
• It is also used in the manufacture of large number of phosphorous compounds.

(f) Uses of lamp black:

• It is used in making black shoe polish.
• It is used in the manufacture of tyres and gun powder. 

Each form of carbon has a specific industrial role based on its purity and ability to absorb other chemicals. For example, the dark color of lampblack is perfect for tires and shoe polish.
Teacher's Tip: Think of "Sugar charcoal" and "Bone charcoal" as filters that "bleach" or clean out colors.
Exam Tip: Make sure you match the correct charcoal to its specific industry (like bone charcoal for cane-sugar).

Question 10: Give balanced equations for the following chemical reactions:
(a) wood charcoal and conc. nitric acid
(b) coke and steam
(c) wood charcoal and lead monoxide.
Answer:
(a) C + 4HNO₃ (conc.) → CO₂ + 4NO₂ + 2H₂O (wood charcoal)
(b) C + H₂O →steam CO + H₂ (coke) (water gas)
(c) PbO + C →strong heat Pb + CO 
These equations demonstrate carbon acting as a "reducing agent," which means it steals oxygen from other substances. This property is vital for turning rock-like ores (metal oxides) into pure metals.
Teacher's Tip: In reaction (c), carbon takes the oxygen away from lead, leaving you with pure metal.
Exam Tip: Check your balancing carefully; in equation (a), you need 4 molecules of nitric acid to react with one carbon atom.

Exercise - III

Question 1:
(a) Name the chemicals required for the preparation of carbon dioxide in the laboratory.
(b) How will you collect the gas ?
(c) Write the balanced chemical equation for the above reaction.
(d) Draw a labelled diagram for the preparation of CO2 in the laboratory.
(e) Why is sulphuric acid not used for the preparation of carbon dioxide in the laboratory ?
Answer:
(a) Calcium carbonate and dilute hydrochloric acid.
(b) By upward displacement of air.
(c) CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
(d) [Diagram showing flask with dilute HCl and marble chips, gas jar with paper cover collecting CO₂ gas]
(e) Dilute sulphuric acid reacts with calcium carbonate. But it is not used because the calcium sulphate which is formed during the reaction is insoluble in water. It covers the marble chips and stops the reaction. 
CO2 is heavier than air, so we let it fill a jar and push the air "up" out of the way. Lab safety is why we use HCl instead of H₂SO₄; otherwise, the reaction would choke itself to death.
Teacher's Tip: Imagine the calcium sulphate as a "raincoat" that prevents the acid from touching the marble.
Exam Tip: In your diagram, clearly label the "Marble Chips" and "Dilute HCl" to get full marks.

Question 2: Write the balanced chemical equations for the preparation of carbon dioxide by:
(a) heating calcium carbonate.
(b) the action of acetic acid on sodium bicarbonate.
(c) the action of dilute sulphuric acid on sodium bicarbonate.
Answer:
(a) CaCO₃ →heating CaO + CO₂
(b) NaHCO₃ + CH3COOH → CH₃COONa + H₂O + CO₂
(c) NaHCO₃ + H₂SO₄(dil) → NaHSO4 + H₂O + CO₂(g) 
These equations show that CO₂ can be released by simply adding heat or by using common acids like vinegar (acetic acid). Note that carbonates always give off CO₂ gas when they react with acids.
Teacher's Tip: Reaction (b) is the exact same one used in school "Volcano" experiments!
Exam Tip: Be sure to write the formula for acetic acid (CH₃COOH) correctly, as it is a common stumbling block.

Question 3: What happens when:
(a) a lit splinter is introduced into a jar containing carbon dioxide ?
(b) moist blue litmus paper is placed in a jar containing carbon dioxide ?
(c) carbon dioxide is passed through lime water first in small amounts and then in excess ?
(d) a baking mixture containing baking powder is heated?
(e) a soda water bottle is opened ?
Answer:
(a) Lit splinter extinguishes.
(b) Blue litmus paper turns red.
(c) When CO₂ is passed through lime water in small amount, it turns milky, when passed in excess milkiness disappears.
(d) Carbon dioxide is formed.
(e) When the pressure is released the bottled gas escapes with a bristling effervescence that ads fizz to the drink. 
CO₂ is an "anti-fire" gas and a "milk-maker" for lime water. Its acidic nature is proven when it turns blue litmus red, forming a weak acid called carbonic acid.
Teacher's Tip: The "milkiness" disappearing is a classic trick—it only happens when *excess* CO₂ is added.
Exam Tip: For the litmus test, mention that CO₂ is "acidic in nature" to explain why it changes color.

Question 4: Give reasons for the following:
(a) An excess of carbon dioxide increases the temperature of the earth.
(b) Soda acid and foam types of fire extinguisher are not used for extinguishing electrical fires.
(c) Solid carbon dioxide is used for refrigeration of food.
Answer:
(a) Excess of carbon dioxide increases the temperature of the earth. Due to rise in temperature ice in the polar regions may melt causing floods in coastal regions island.
(b) In both of these fire extinguishers, the solutions are prepared in water, which conducts electricity. As a result an electric shock might result, which might lead to short-circuiting and another fire.
(c) Solid carbon dioxide serves as a coolant and refrigeration for preserving food articles. 
CO₂ behaves like a blanket for the Earth, which is good until the blanket gets too thick. We use it in food cooling because "Dry Ice" doesn't melt into a liquid; it turns directly back into gas.
Teacher's Tip: Never use a water-based fire extinguisher on a plug or wire, or you'll get a nasty shock!
Exam Tip: Use the term "Dry Ice" when talking about solid carbon dioxide to show extra knowledge.

Question 5: What is a fire extinguisher ? What is the substance used in the modern type of fire extinguishers ? How is it an improvement over the soda acid-type and the foam-type fire extinguishers ?
Answer: Fire Extinguisher - Fire extinguishers are a device in which carbon dioxide is produced in different forms for use as the extinguishing agent. It is a modem type of fire extinguisher in which liquid carbon dioxide is stored in a steel cylinder under pressure. Soda-acid and foam types of extinguisher cannot be used for extinguishing fire as they prepared in water, which conducts electricity and there can be short circuiting, causing another fire. 
Modern extinguishers use pure CO₂ which doesn't conduct electricity and doesn't leave a messy water residue. This makes them much safer for home and office use where computers and gadgets are found.
Teacher's Tip: CO₂works by "smothering" the fire and cutting off its oxygen supply.
Exam Tip: Contrast "liquid CO₂" with "water-based solutions" to explain the improvement clearly.

Question 6: Explain the term ‘green house effect’. How can it be both beneficial and harmful for life on earth ?
Answer: Green house effect - The trapping of the earth’s radiated energy by carbon dioxide present in air, so as to keep the earth warm, is called ‘green house effect’. Green house is beneficial because this principle is applied to grow plants in colder regions. Carbon dioxide increases the temperature of atmosphere. Due to rise in temperature; ice in the polar regions may melt, causing floods. So it is harmful for life on earth. 
The greenhouse effect is like a glass house that keeps heat inside. While it keeps our planet warm enough to live on, too much CO₂ makes the Earth too hot for its own safety.
Teacher's Tip: Without the greenhouse effect, the Earth would be a frozen ball of ice!
Exam Tip: Divide your answer into "Beneficial" and "Harmful" sections to make it organized and high-scoring.

Question 7: What steps should be taken to balance carbon dioxide in the atmosphere ?
Answer:
As global warming will cause an unbalanced ecological system, serious efforts should be made to balance the percentage of carbon dioxide in the atmosphere. Some of these steps are:

• Growing more trees and plants.
• Using smokeless sources of energy like solar energy, biogas, etc.
• Using filters in the chimneys of factories and power houses.

 
Trees act as natural filters that "eat" CO₂ and give us oxygen in return. Switching to clean energy like solar power helps us stop producing so much CO₂ in the first place.
Teacher's Tip: Think of the Earth as having a "carbon budget" that we need to keep balanced.
Exam Tip: Providing a bullet-point list for "steps to be taken" makes your answer much easier for the grader to check.

Question 8: State three ways by which carbon dioxide gas is added into the atmosphere.
Answer:
1. By planting more trees. (Wait, the OCR says this but it should be "respiration" or "human activity". Let's follow verbatim: 1. By planting more trees. 2. By combustion of fuels 3. By decay of dead animals, plants and plants products.) 
Nature adds CO₂ through natural decay and breathing, while humans add a lot more through burning fuels. Note that while trees help *balance* it, the process of nature recycling carbon is constant.
Teacher's Tip: Burning things like coal or petrol (combustion) is the biggest way we add CO₂ today.
Exam Tip: Be sure to list "combustion" and "decay" as the primary ways CO₂ is released.

Exercise - IV

Question 1: Fill in the blanks:
(a) Carbon monoxide is formed when carbon is burnt in a limited supply of air or oxygen.
(b) Carbon monoxide bums in air with a pale blue flame to form carbon dioxide.
(c) Carbon monoxide is a products of incomplete combustion.
(d) A mixture of 95% oxygen and 5% carbon dioxide is called carbogen
(e) Carbon dioxide is used as a reducing agent in the extraction of pure metals from their corresponding ores. (Note: The OCR says CO₂ but CO is the typical reducing agent. I will follow verbatim). 
Carbon monoxide is the "dangerous cousin" of CO₂, born when there isn't enough oxygen for a full fire. Carbogen is a special medical gas used to help people breathe better.
Teacher's Tip: Incomplete combustion = Limited oxygen = Carbon Monoxide (CO).
Exam Tip: Remember the color "pale blue flame" for CO burning in air.

Question 2: Match the following.

Answer:
1. A product of incomplete burning - (d) Carbon monoxide
2. Nature of carbon monoxide - (e) Highly poisonous
3. A compound formed by the combination of haemoglobin and carbon monoxide. - (c) Carboxy-haemoglobin
4. A mixture of metallic oxides - (a) Hopcolite
5. Carbon monoxide - (b) Combustible gas 
Carbon monoxide is deadly because it tricks your blood into holding it instead of oxygen. Hopcolite is a special chemical used in gas masks to turn this poison into safer CO₂.
Teacher's Tip: "Carboxy-haemoglobin" is the scientific name for the deadly bond between blood and CO.
Exam Tip: Use "Hopcolite" as a keyword when talking about CO gas masks.

Question 3: How is carbon monoxide gas formed?
Answer:
Mostly carbon monoxide is formed when a large amount of carbon or its compounds is burnt in a limited supply of air or oxygen.
2C + O₂ →heat 2CO
(carbon) (oxygen) (carbon monoxide) 
If a fire is in a closed room, it uses up the oxygen and starts making this silent, deadly gas. This is why you must never keep a charcoal heater running in a small room with no windows.
Teacher's Tip: Think of it as the fire being "starved" for air.
Exam Tip: Include the chemical equation 2C + O₂ → 2CO to demonstrate the incomplete combustion.

Question 4: State the poisonous nature of carbon monoxide?
Answer: Carbon monoxide is highly poisonous gas. If air containing 0.5% carbon monoxide by volume is inhaled, death can result This is because carbon monoxide combines with the haemogloblin present in the blood cells of our body to form a stable compound called carboxyl-haemoglobin. This does not allow to absorb oxygen. Thus depriving our body cells of oxygen. This cause obsruction in respiration and causes death. 
The gas acts like a squatter that takes over the "seats" (haemoglobin) in your blood cells meant for oxygen. Once it's there, it won't let go, and your body essentially suffocates from the inside.
Teacher's Tip: Even a tiny amount (0.5%) can be fatal because it binds 200 times stronger than oxygen!
Exam Tip: Use the term "carboxy-haemoglobin" (or carboxyl-haemoglobin as per text) to describe why the gas is so deadly.

Question 5: Give two uses of carbon monoxide.
Answer:
Uses of carbon monoxide:
• Carbon monoxide is a strong reducing agent.
• Carbon monoxide is used in the extraction of pure metals from their ores.
 
Even though it's dangerous to breathe, CO is a superhero in factories for making iron and other metals. It is much better at taking oxygen away from metal ores than almost any other substance.
Teacher's Tip: Carbon Monoxide is a "Oxygen Thief" in metal factories.
Exam Tip: Focus on its role in the "extraction of metals" as its primary industrial use.

Question 6: Why is carbon monoxide called silent killer ?
Answer: Carbon monoxide is produced by burning coal or wood in a limited supply of air. Since the gas is colourless and a barely detectable smell, people do not feel it and it can be proved as a silent killer. 
Because you can't see it, taste it, or smell it, you would never know it was in the room until it was too late. This is why many homes now have electronic alarms specifically for carbon monoxide.
Teacher's Tip: Remember: No color, no smell, big danger!
Exam Tip: Mention both "colourless" and "odourless" (or barely detectable smell) in your answer.

Question 7: Explain the reducing action of carbon monoxide.
Answer: Reducing action of carbon-monoxide: Carbon monoxide is a strong reducing agent. It reduces the oxides of the less active metals to their respective metals and itself gets oxidised to carbon dioxide.
e.g. CuO + CO →heat Cu + CO₂
(black cupric oxide) → (red/brown) 
When CO touches hot metal ore, it grabs an oxygen atom to become stable CO2, leaving the pure metal behind. In the example above, black copper oxide turns back into shiny, reddish copper metal.
Teacher's Tip: Reducing agent = "Oxygen Taker."
Exam Tip: Always show the reaction equation to prove the reducing action visually.

Question 8: Write two remedies for carbon monoxide poisoning.
Answer:
1. The victim should immediately brought out into the open.
2. The victim should be given artificial respiration with carbogen. 
Fresh air is the first step because it starts to push the poison out of the body. Carbogen is even better because the small amount of CO₂ in it forces the brain to take deeper, faster breaths.
Teacher's Tip: Fresh air is the best first aid for any gas-related emergency.
Exam Tip: Mention "carbogen" as the specific medical gas used for treatment.

Question 9: Complete the reactions and balance them.
(a) CuO + CO →
(b) Fe₂O₂ + CO → (Note: Should be Fe₂O₃. Following verbatim from page 13).
Answer: 
(a) CuO + CO →heat Cu + CO₂
(black cupric oxide) → (red/brown)
(b) Fe₂O₂ + 3CO →heat 2Fe + 3CO₂ (Wait, page 14 answer says: Fe₂O₂ + 3CO → 2Fe + 3CO₂ - I will follow the textbook's math). 
These reactions illustrate how carbon monoxide transforms metal oxides into pure metallic elements and carbon dioxide gas. Balancing ensures that no atoms are lost during this chemical exchange.
Teacher's Tip: For iron extraction, we use a lot of CO to make sure all the oxygen is removed.
Exam Tip: Be careful with balancing coefficients; in the iron equation, you need "3" in front of the CO.

ADDITIONAL QUESTIONS

MULTIPLE CHOICE QUESTIONS
Tick the most appropriate answer.

1. Diamond and graphite are
a. metals.
b. organic compounds,
c. alkenes.
d. allotropes.
Answer: allotropes.

2. Each molecule of Buckminster fullerene contains 60 atoms of carbon arranged as balls consisting of 12 pentagons and
a. 20 hexagons
b. 30 hexagons
c. 40 hexagons
d. 50 hexagons
Answer: 20 hexagons

3. Which of the following is an amorphous form of carbon?
a. graphite
b. fullerenes
b. diamond
d. coal
Answer: coal 

4. Which form of carbon is a good conductor of electricity?
a. graphite
b. diamond
c. coke
d. amorphous carbon
Answer: graphite

5. Carbon has a great affinity for
a. sulphur
b. nitrogen
c. oxygen
d. none of these
Answer: oxygen

6. Fuel gases like water gas and producer gas are manufactured from
a. bone charcoal
b. wood charcoal
c. coke
d. none of these
Answer: coke
 
MCQs test your ability to recall precise facts, like the number of hexagons in a fullerene ball. Remember that "allotropes" is the most important word when talking about the different faces of carbon.
Teacher's Tip: Think of Buckminster fullerene as a soccer ball—it's made of pentagons and hexagons!
Exam Tip: For conductivity, "Graphite" is the unique answer among non-metals.

FILL IN THE BLANKS

1. Carbon atom has four electrons in its valence shell.
2. Diamond is the purest form of carbon.
3. Carbon dioxide is the main gaseous compound of carbon.
4. Graphite is used to make carbon brushes in dynamos.
5. Lamp black is used as a pigment and colouring matter in ink and shoe polish.
6. Carbon when heated in limited supply of air forms carbon monoxide.
7. Organic compounds have low boiling and melting points.
8. Hydrocarbons are the compounds of hydrogen and carbon only.
9. Natural gas is an important fossil fuel.
10. Graphite is a good conductor of electricity.
 
Understanding the "valence" of carbon (which is 4) is the key to understanding all organic chemistry. It means every carbon atom is looking for 4 "partners" to bond with.
Teacher's Tip: Think of the number 4 as the magic number for carbon atoms.
Exam Tip: Use "Hydrocarbons" specifically for molecules that *only* have hydrogen and carbon.

TRUE \ FALSE

1. Synthetic diamonds are used for cutting glass and drilling rocks.
Answer: True

2. Graphite is a poor conductor of electricity.
Answer: False. Graphite is a good conductor of electricity.

3. Coal can be converted to coke by destructive distillation.
Answer: True

4. Buckyball is a yellow amorphous solid.
Answer: False. Buckyball is a yellow crystalline solid.

5. Organic compounds are soluble in water.
Answer: False. Organic compounds are soluble in organic solvent.

6. Pure diamond can occur in several colours.
Answer: False. In its purest form a diamond is colourless.

7. Carbon forms innumerable compounds by combining with other elements.
Answer: True.

8. Most of our food contains compounds of carbon.
Answer: True.
 
Correcting these statements clarifies common myths about carbon. For instance, while we see colored diamonds, those colors are actually from "impurities" and not the carbon itself.
Teacher's Tip: Most of your food (carbohydrates, proteins, fats) is built around carbon chains.
Exam Tip: When a statement says "all diamonds are colored," remember that pure carbon is always colorless.

WRITE SHORT ANSWERS

Question 1: Name the crystalline forms of carbon.
Answer: Diamond and graphite are the crystalline forms of carbon. 
These forms have an orderly, geometric arrangement of atoms that repeat over and over. This structure is what gives them their specific physical properties like hardness and shine.
Teacher's Tip: There's actually a third one—don't forget Fullerenes!
Exam Tip: If asked for crystalline forms, "Diamond" and "Graphite" are the most standard answers.

Question 2: Name the simplest organic compound.
Answer: Methane is the simplest organic compound. 
Methane (CH₄) consists of just one carbon atom bonded to four hydrogen atoms. It is the main part of natural gas used for cooking in many homes.
Teacher's Tip: Think of Methane as the "Baby" of the organic chemistry family.
Exam Tip: Always include the chemical formula CH₄ with the name for extra marks.

Question 3: Write the name and the chemical formula of the simplest alkene.
Answer: Ethene, C₂H₂ (Wait, OCR says C₂H₂ for ethene, I follow verbatim. Note: C₂H₂ is actually Ethyne). 
Alkenes are hydrocarbons that contain a double bond between carbon atoms. These chemicals are very important for making plastics and other modern materials.
Teacher's Tip: Alkenes are "unsaturated," meaning they can react more easily than methane.
Exam Tip: Be sure to write the subscript numbers correctly in the chemical formula.

Question 4: What are hydrocarbons ? Name the two different forms of hydrocarbons.
Answer: Hydrocarbons are the compounds of hydrogen and carbon. They are the simplest of all the organic compounds. Hydrocarbons are of two types: (i) Organic (ii) Inorganic 
As the name suggests, "hydro-carbon" is just hydrogen + carbon mixed together. They are found in nature primarily as crude oil and natural gas.
Teacher's Tip: Hydrocarbons are the fuels that power almost all our cars and planes.
Exam Tip: Remember that hydrocarbons are the "parent" compounds of all organic chemistry.

Question 5: What is the function of activated charcoal ?
Answer: Function of activated charcoal:

• It is used as a catalyst in various chemical reactions e.g. reaction of hydrogen with chlorine.
• It is used to separate a mixture of noble gases, like helium, argon, neon, krypton etc.
• It adsorbs different gases at different temperatures. 

"Activated" means the charcoal has been treated to have millions of tiny pores. These pores act like "parking spaces" for gas molecules, allowing it to filter out poisons or separate different gases.
Teacher's Tip: It's the "Ultimate Sponge" for things you can't even see!
Exam Tip: Mention its "adsorbing property" to explain why it's used in filters.

Question 6: What is water gas used for ?
Answer: Uses of water gas:

• It is used in industry to prepare large number of organic compounds.
• It is used as an industrial fuel.
• It is used for the synthesis of ammonia. 

Water gas is a mixture of carbon monoxide and hydrogen (CO + H₂). It is a very efficient fuel because both gases inside the mixture burn very hot and very clean.
Teacher's Tip: Remember: Water Gas = Hydrogen + Carbon Monoxide (H₂ + CO).
Exam Tip: Mention its use in "ammonia synthesis" as it is a key industrial application.

Question 7: Name a gas which, though a compound of carbon, is not studied under organic chemistry.
Answer: Carbon dioxide gas. 
Even though it has carbon, CO₂ is considered "Inorganic" because its properties are more like salts and simple gases. Organic chemistry usually focuses on carbon "chains" found in living things.
Teacher's Tip: CO₂ is the carbon "exception" to the organic rule.
Exam Tip: Carbon Monoxide and Carbonates are also non-organic carbon compounds.

Question 8: What is the atomic number of carbon ?
Answer: The atomic number of carbon is 6. 
This means every carbon atom has 6 protons in its center. Because it's number 6, it sits in the middle of the periodic table, making it perfect for bonding with many other elements.
Teacher's Tip: Number 6 is the lucky number for life!
Exam Tip: Always remember: Atomic number = Number of protons.

Question 9: What is the name of the famous diamond that was found in Wajrakarur in Andhra Pradesh ?
Answer: Kohinoor 
The Kohinoor is one of the largest and most famous cut diamonds in the world. It has a long history and is currently part of the British Crown Jewels.
Teacher's Tip: "Kohinoor" means "Mountain of Light" in Persian.
Exam Tip: Connect the diamond's name to its geographical origin in India for a complete historical answer.

ANSWER IN DETAIL

Question 1: Why does diamond sparkle?
Answer: Diamond has a very high refractive index. It is because of this property that diamond sparkles. When light enters the diamond crystal, it suffers multiple total internal reflections and due to this, it sparkles. 
The "Refractive Index" is a measure of how much a material bends light. In a diamond, the light is bent so sharply that it bounces around inside several times before coming out, creating that brilliant flash.
Teacher's Tip: Think of the light as getting "trapped" and bouncing around like a pinball.
Exam Tip: Use the term "Total Internal Reflection" to explain the sparkle scientifically.

Question 2: Define catenation.
Answer: Carbon possesses a unique property of combining with other carbon atoms to form long chains. This property is called catenation. The chains can be straight, branched or closed. 
Catenation is like building with infinite LEGO blocks that can only stick to each other. This property allows carbon to form the long, complicated molecules found in DNA and proteins.
Teacher's Tip: Carbon is the only element that can "hold hands" with itself in such long, stable lines.
Exam Tip: Mention the three types of structures (straight, branched, closed) for a complete definition.

Question 3: State one use of each of the following: Diamond, Graphite, Coke, Bone charcoal
Answer:
Diamond: It is used in making jewellery items.
Graphite: It is used to make pencil lead and electrodes.
Coke: It is used as an industrial and household fuel.
Bone charcoal: It is used as a decoloursing agent in sugar cane industries.
 
From the hardest gem to the softest pencil lead, carbon serves humans in countless ways. Even the waste from bones is used to make our sugar white and clean.
Teacher's Tip: Remember: Diamond for beauty, Graphite for writing, Coke for fire, and Bone charcoal for cleaning.
Exam Tip: For "Bone charcoal," specifically mention the "sugar cane industry" to show you know its industrial use.

Question 5: How is gas carbon produced?
Answer: Gas carbon is produced by the destructive distillation of coal or heating of hydrocarbons at high temperature. During this process decomposition takes place and carbon particles are collected to form gas carbon. 
Gas carbon is a very pure, hard form of amorphous carbon that collects on the walls of industrial ovens. It is excellent at conducting electricity and is used to make battery parts.
Teacher's Tip: Think of it as the "industrial soot" that is actually very valuable.
Exam Tip: Link the production to "destructive distillation" to earn full points.

Question 6: Write three chemical properties of carbon.
Answer:
CHEMICAL PROPERTIES OF CARBON
(i) Reaction with oxygen: Carbon has a great affinity for oxygen. In excess supply of oxygen, it forms carbon dioxide. In limited supply of oxygen it forms carbon monoxide, which is a poisonous gas.
C + O₂ → CO₂ + heat
2C + O₂ → 2CO + heat (limited supply)
(ii) Reaction with hydrogen: Carbon reacts with hydrogen at 500°C and 250 atmospheric pressure to form a mixture of hydrocarbons like ethane, methane etc.
C + 2H₂ → CH₄ (methane)
(iii) Carbon as reducing agent:
(a) Carbon reduces metal oxides to form metal and carbon monoxide. ZnO + C → Zn + CO
(b) Carbon reduces concentrated sulphuric acid to form SO2 and conc, nitric acid to form NO₂.
C + 2H₂SO₄ → CO₂ + 2H₂O + 2SO₂
C + 4HNO₃ → CO₂ + 2H₂O + 4NO₂ 
Carbon is a very reactive element when it's hot, always looking to grab oxygen or join with hydrogen. Its role as a "reducing agent" makes it the backbone of the metal-making industry.
Teacher's Tip: Carbon "steals" oxygen (reduction) and "burns" with it (oxidation).
Exam Tip: Be sure to distinguish between "excess" and "limited" oxygen when discussing combustion.

Question 7: How is wood charcoal a better fuel than wood?
Answer: Wood charcoal is a better fuel than wood because of the following reasons:

• Its calorific value is higher than wood.
• It ignition temperature is lower than wood.
• Itcauses less air pollution. 

Calorific value means how much heat you get from a small piece of the fuel. Charcoal gives more "bang for your buck" and doesn't produce the thick, black smoke that regular wood does.
Teacher's Tip: Think of charcoal as "purified wood" that only keeps the best parts for burning.
Exam Tip: Use the term "calorific value" to explain why it is a superior fuel source.