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Chapter: 9th Science : Chemistry : Carbon and its Compounds

Answer the following questions

Science : Chemistry : Carbon and its Compounds : Book Back Important Questions, Answers, Solutions : Answer briefly, Answer in detail, Exercise Numerical Problems, Intext Activities





IV. Answer briefly:


1. Differentiate graphite and diamond.



• Each carbon atom has three covalent bonds.

• Soft, slippery to touch and opaque

• It has planar layers of hexagon units.

• It is conductor of heat and electricity.


• Each carbon atom has four covalent bonds.

• Hard, heavy and transparent

• It has tetrahedral units linked in three dimension

• It is non-conductor of heat and electricity


2. Write all possible isomers of C4 H10.



3. Carbon forms only covalent compounds. Why?

Answer: Carbon forms only covalent compounds because it has 4 electrons, in its.


4. Define Allotrophy.

Answer: Allotrophy is a property by which are element can exist in more than one form that are physically different and chemically similar.


5. Why are one-time use and throwaway plastics harmful?

Answer: 1. Use and throwaway plastics cause short and long-term environmental damage.

2. Half of all the plastic made today is used for throwaway plastic items. These block drains and pollute water bodies.

3. One-time use plastic causes health problems for humans, plants and animals.

4. Some examples are plastic carry bags, cups, plates, straws, water pouches, cutlery and plastic sheets used for food wrapping.


V.Answer in detail:


1. What is catenation? How does carbon form catenated compounds?


Catenation is binding of an element to itself or with other elements through covalent bonds to form open chain or closed chain compounds.

(i) Carbon is the most common element which undergoes catenation and forms long chain compounds.

(ii) Carbon atom links repeatedly to itself through covalent bond to form linear chain, branched chain (or) ring structure.

 (iii) This property of carbon itself is the reason for the presence of large number of organic carbon compounds.

(iv) So organic chemistry essentially deals with catenated carbon compounds.

(v) Example: Starch and cellulose contain chains of hundreds of carbon atoms.


2. What are the chemical reactions of carbon?

Answer: Elemental carbon undergoes no reaction at room temperature.

Oxidation: Carbon combines with oxygen to form its oxides such as carbon monoxide (CO) and carbon dioxide (CO2), with evolution of heat. Organic carbon compounds like hydrocarbon also undergo oxidation to form oxides and steam with evolution of heat and flame.

This reaction is also called ‘Combustion’.

2C(S) + O2(g) → 2CO(g) + heat.

C(s) + O2(g) → CO2(g) + heat.

CH4(g) +2O2(g) → CO2(g) + 2H2O(g) + heat.

Reaction with Steam: Carbon reacts with steam to form carbon monoxide and hydrogen. This mixture is called water gas.

C(S) +H2O(g) → CO(g) + H 2(g)

Reaction with Sulphur: With sulphur, carbon forms its disulphide at high temperature.

C(S) + 2S(g) → CS2(g)

Reaction with Metals: At elevated temperatures, carbon reacts with some metals like iron, tungsten, titanium, etc., to form their carbides.

Tungesten + Carbon → Tungesten carbide

W + C → WC.


3. Name the three safer resin codes of plastics and describe their features.



VI. Higher Order Thinking Skills:


1. Why do carbon exist mostly in combined state?

Answer: 1.Carbon is found in free state as well as combined state in nature.

2. Due to the following properties, carbon can form innumerable compounds.

1) Catenation, 2) Tetravalency, 3) Multiple bonds, 4) Isomerism, 5) Allotropy.


2. When a carbon fuel burns in less aerated room, it is dangerous to stay there. Why?


1. When a carbon fuel burns in less aerated room, the fuel may undergo incomplete combustion.

2. It results in the formation of carbon monoxide.

3. When exposed to carbon monoxide (CO) it enters human body, through breathing, affects the function of haemoglobin.

4. Sometimes, it will lead to death.


3. Explain how dioxins are formed? Which plastic type they are linked to and why they are harmful to humans?


Dioxin formation:

1. Dioxin compounds are not created intentionally, but are formed inadvertently by a number of human and natural activities.

2. These activities include combustion and incineration, forest fires, chlorine bleaching of pulp and paper, certain types of chemical manufacturing and processing, and other industrial processes.

3. Cigarette smoke, some home-heating systems, and exhaust from vehicles using leaded and unleaded petrol as well as diesel fuels also produce small amounts of dioxins.

4. Burning materials that may contain chlorine such as plastics, wood treated with pentachlorophenol (PCP), pesticide-treated wastes, other chemicals such as polychlorinated biphenols (PCBs), and even bleached paper can produce dioxins.

Their link with plastic:

1. Dioxins are linked with PVC (Polyvinyl Chloride plastics).

2. The most dangerous emissions can be caused by burning PVC, as it releases dioxins.

Harmful effects of Dioxins to humans:

1. Dioxins are the most toxic to the human organisms.

2. Dioxins can cause cancer, disrupt the endocrine system, alteration in pituitary and thyroid gland functions, immune suppression, neurobehavioral effects and cause reproductive and developmental effects.

3. They are carcinogenic and a hormone disruptor and persistent, and they accumulate in our body-fat and thus mothers give it directly to their babies via the placenta.


4. Yugaa wants to buy a plastic water bottle. She goes to the shop and sees four different kinds of plastic bottles with resin codes 1,3,5 and 7. Which one should she buy? Why?

Answer: 1.Yugaa should buy a plastic water bottle with Resin Code No.5, which is considered as one of the safer plastics. It is light and hard. 

Reasons to avoid resin codes 1, 3, 7

1. Bottle with Resin Code 1 is to be used only once. This plastic can release a chemical additive called antimony, which is not good for health.

2. Bottle with Resin Code 3 is most toxic plastic. It will have a smell of a new shoe. It should be avoided.

3. Bottle with Resin Code 7 has the plastic types PC and ABS which are unsafe and toxic.


Intext activities



With the help of your teacher, try to classify the following as organic and inorganic compounds.

HCN, CO2, Propane, PVC,CO Keroserie, LPG, Coconut oil, Wood , Perfume, Alcohol, Na2CO3, CaCO3, MgO, Cotton, Petrol.











Wood, kerosene,coconut oil








Take a football since it resembles to Buckminster fullerene. Count how many hexagonal and pentagonal panels are in it. Every corner is considered as one carbon. Compare your observation with fullerene and discuss with your friends.


To compare the structure of fullerene with football

Materials required:

Foot ball


1. Take a foot ball.

2. Count the hexagonal and pentagonal rings shapes in foot ball.


Shapes Fullerene (CAft) Foot ball


The structure of foot ball is compared with fullerene. 

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