Lesson: Carbon and its Compounds

Question: 1

Carbon exists in the atmosphere in the form of:

(a) Carbon monoxide only

(b) Carbon monoxide in traces and carbon dioxide

(d) Coal

Solution:

Question:2

Which of the following statements are usually correct for carbon compounds?

(i) are good conductors of electricity

(ii) are poor conductors of electricity

(iii) have strong forces of attraction between their molecules

(iv) do not have strong forces of attraction between their molecules

(a) (i) and (iii)

(b) (ii) and (iii)

(d) (ii) and (iv)

Solution:

Question:3

A molecule of ammonia ( $N H_{3}$ ) has:

(a) Only single bonds

(b) Only double bonds

(d) Two double bonds and one single bond

Solution:

Question: 4

Buckminsterfullerene is an allotropic form of:

(a) Phosphorus

(b) Sulphur

(d) Tin

Solution:

Question: 5

Which of the following are correct structural isomers of butane?

(a) (i) and (iii)

(b) (ii) and (iv)

(d) (iii) and (iv)

Solution:

Question:6

${CH}_{3} COOH \overset{Heat {+Alkaline KMnO}_{4}}{\to} {CH}_{3} COOH$

In the above given reaction, alkaline $K M n O_{4}$ acts as:

(a) Reducing agent

(b) Oxidising agent

(d) Dehydrating agent

Solution:

Question:7

Oils on treating with hydrogen in the presence of palladium or nickel catalyst form fats.

This is an example of:

(a) Addition reaction

(b) Substitution reaction

(d) Oxidation reaction

Solution:

Question: 8

In which of the following compounds, $—$ OH is the functional group?

(a) Butanone

(b) Butanol

(d) Butanal

Solution:

Question: 9

The soap molecule has a:

(a) Hydrophilic head and a hydrophobic tail

(b) Hydrophobic head and a hydrophilic tail

(d) Hydrophilic head and a hydrophilic tail

Solution:

Question: 10

Which of the following is the correct representation of electron dot structure of nitrogen?

Solution:

Question: 11

Structural formula of ethyne is:

Solution:

Question: 12

Identify the unsaturated compounds from the following:

(i) Propane

(ii) Propene

(iii) Propyne

(iv) Chloropropane

(a) (i) and (ii)

(b) (ii) and (iv)

(d) (ii) and (iii)

Solution:

Question: 13

Chlorine reacts with saturated hydrocarbons at room temperature in the:

(a) Absence of sunlight

(b) Presence of sunlight

(d) Presence of hydrochloric acid

Solution:

Question: 14

In the soap micelles:

(a) The ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.

(b) Ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster.

(d) Both ionic end and carbon chain are on the exterior of the cluster

Solution:

Question: 15

Pentane has the molecular formula $C_{5} H_{12}$ . It has:

(a) 5 covalent bonds

(b) 12 covalent bonds

(d) 17 covalent bonds

Solution:

Question: 16

Structural formula of benzene is:

Solution:

Question: 17

Ethanol reacts with sodium and forms two products.

These are:

(a) Sodium ethanoate and hydrogen

(b) Sodium ethanoate and oxygen

(d) Sodium ethoxide and oxygen

Solution:

Question: 18

The correct structural formula of butanoic acid is:

Solution:

Question: 19

Vinegar is a solution of:

(a) $50 % - 60 %$ acetic acid in alcohol

(b) $5 % - 8 %$ acetic acid in alcohol

(d) $50 % - 60 %$ acetic acid in water

Solution:

Question: 20

Mineral acids are stronger acids than carboxylic acids because

(i) Mineral acids are completely ionised

(ii) Carboxylic acids are completely ionised

(iii) Mineral acids are partially ionised

(iv) Carboxylic acids are partially ionised

(a) (i) and (iv)

(b) (ii) and (iii)

(d) (iii) and (iv)

Solution:

Question: 21

Carbon forms four covalent bonds by sharing its four valence electrons with four univalent atoms, e.g. hydrogen. After the formation of four bonds, carbon attains the electronic configuration of:

(a) Helium

(b) Neon

(d) Krypton

Solution:

Question: 22

The correct electron dot structure of a water molecule is:

Solution:

Question: 23

Which of the following is not a straight chain hydrocarbon?

Solution:

Question; 24

Which among the following are unsaturated hydrocarbons?

(a) (i) and (iii)

(b) (ii) and (iii)

(d) (iii) and (iv)

Solution:

Question: 25

Which of the following does not belong to the same homologous series?

(a) $C H_{4}$

(b) $C_{2} H_{6}$

(d) $C_{4} H_{8}$

Solution:

Question: 26

The name of the compound $C H_{3} — C H_{2} — C H O$ is:

(a) Propanal

(b) Propanone

(d) Ethanal

Solution:

Question: 27

The heteroatoms present in $C H_{3} — C H_{2} — O — C H_{2} — C H_{2} C l$ are:

(i) Oxygen

(ii) Carbon

(iii) Hydrogen

(iv) Chlorine

(a) (i) and (ii)

(b) (ii) and (iii)

(d) (i) and (iv)

Solution:

Question: 28

Which of the following represents saponification reaction?

(a) $C H_{3} C O O N a + N a O H^{\overset{C a O}{\to}} C H_{4} + N a_{2} C O_{3}$

(b) $C H_{3} C O O H + C_{2} H_{5} O H^{\overset{H_{2} S O_{4}}{\to}} C H_{3} - C O O - C_{2} H_{5} + H_{2} O$

(d) $C H_{3} C O O C_{2} H_{5} + N a O H \to C H_{3} C O O N a + C_{2} H_{5} O H$

Solution:

Question: 29

The first member of alkyne homologous series is:

(a) Ethyne

(b) Ethene

(d) Methane

Solution:

Question: 30

Draw the electron dot structure of ethyne and also draw its structural formula:

Solution:

Structural formula of ethyne

H C C H

Electron dot structure of ethyne ( $C_{2} H_{2}$ )

Question: 31

Write the names of the following compounds:

Solution:

(a) Pentanoic acid

(b) Butyne

(d) Pentanol

Question: 32

Identify and name the functional groups present in the following compounds.

Solution:

Question: 33

A compound X is formed by the reaction of a carboxylic acid $C_{2} H_{4} O_{2}$ and an alcohol in presence of a few drops of $H_{2} S O_{4}$ . The alcohol on oxidation with alkaline $K M n O_{4}$ followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of (a) carboxylic acid, (b) alcohol and (c) the compound X. Also, write the reaction.

Solution:

(a) The carboxylic acid is ethanoic acid.

(b) The alcohol is ethanol.

The reaction is as follows:

$\begin{array}{l} C H_{3} C O O H + C_{2} H_{5} O H^{\overset{H_{2} {SO}_{4}}{\to}} C H_{3} C O O C_{2} H_{5} + H_{2} O \\ E t h a n o i c a c i d E t h a n o l E t h y l e t h a n o a t e \end{array}$

Question: 34

Why detergents are better cleansing agents than soaps? Explain.

Solution:

Detergents are better cleansing agents than soaps. This is because detergents are effective even in hard water whereas, soaps cannot be used in hard water for washing clothes or cleaning dirt. This is because the charged ends of detergents do not react with calcium and magnesium ions in hard water to form insoluble precipitate.

Question: 35

Name the functional groups present in the following compounds

(a) $C H_{3} C O C H_{2} C H_{2} C H_{2} C H_{3}$

(b) $C H_{3} C H_{2} C H_{2} C O O H$

(d) $C H_{3} C H_{2} O H$

Solution:

(a) Ketone

(b) Carboxylic acid

(d) Alcohol

Question: 36

How is ethene prepared from ethanol? Give the reaction involved in it.

Solution:

Ethanol dehydrates on heating with concentrated sulphuric acid at 443 K and gives ethane and water.

$C_{2} H_{5} O H \to_{443 K}^{H o t c o n c . H_{2} S O_{4}} C H_{2} = C H_{2} + H_{2} O$

Question: 37

Intake of small quantity of methanol can be lethal. Give comment.

Solution:

Methanol gets oxidised in the liver and forms methanal. Methanal reacts rapidly with the protoplasm and leads to its coagulation. It also blocks the optic nerves leading to blindness.

Question: 38

A gas is evolved when ethanol reacts with sodium. Name the gas evolved and also write the balanced chemical equation of the reaction involved.

Solution:

Hydrogen gas is evolved when ethanol reacts with sodium. The equation for the reaction is:

$2 C H_{3} C H_{2} O H + 2 N a \to 2 C H_{3} C H_{2} O N a + H_{2}$

Question: 39

Ethene is formed when ethanol at 443 K is heated with excess of concentrated sulphuric acid. What is the role of sulphuric acid in this reaction? Write the balanced chemical equation of this reaction.

Solution:

When ethanol is heated to form ethane, sulphuric acid acts as a dehydrating agent in the reaction.

$C_{2} H_{5} O H \to_{443 K}^{H o t c o n c . H_{2} S O_{4}} C H_{2} = C H_{2} + H_{2} O$

Question: 40

Carbon, Group (14) element in the Periodic Table, is known to form compounds with many elements.

Write an example of a compound formed with:

(a) Chlorine (Group 17 of Periodic Table)

(b) Oxygen (Group 16 of Periodic Table)

Solution:

(a) Carbon tetrachloride ( $C C l_{4}$ )

(b) Carbon dioxide ( $C O_{2}$ )

Question: 41

In electron dot structure, the valence shell electrons are represented by crosses or dots.

(a) The atomic number of chlorine is 17. Write its electronic configuration

(b) Draw the electron dot structure of chlorine molecule.

Solution:

(a) Electronic configuration of chlorine:

	K	L	M
Number of electrons	2	8	7

Question: 42

Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.

Solution:

Carbon has a smaller size. Due to its smaller size, carbon exhibits catenation much more than silicon, which has a relatively bigger size. This smaller size makes the C $-$ C bonds strong while the Si $-$ Si bonds are comparatively weaker.

Question: 43

Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.

Solution:

Unsaturated hydrocarbons have double or triple bonds between two carbon atoms. They participate in the addition reaction.

Due to the presence of double bond, these molecules can break one of the carbon-carbon bonds and can add other atoms by sharing of electrons with new atoms.

Thus, addition reaction results in the formation of a saturated compound.

All unsaturated carbon compounds decolorize bromine water whereas all saturated hydrocarbons do not decolorize bromine water.

Ethane and ethene can, thus, be distinguished by the bromine water test.

Question: 44

Match the reactions given in Column (A) with the names given in column (B).

Solution:

(a) $—$ (iv)

(b) $—$ (i)

(d) $—$ (iii)

Question: 45

Write the structural formulae of all the isomers of hexane.

Solution:

Question: 46

What is the role of metal or reagents written on arrows in the given chemical reactions?

Solution:

(a) Ni acts as a catalyst.

(b) Concentrated $H_{2} S O_{4}$ acts as a catalyst.

Question: 47

A salt X is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogen carbonate. Name the salt X and the gas evolved. Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named. Also, write chemical equation of the reaction involved.

Solution:

When ethanoic acid reacts with sodium hydrogen carbonate, sodium ethanoate is formed. Thus, X is sodium ethanoate.

Gas evolved is carbon dioxide.

Activity: The gas that is evolved is passed through lime water. It turns the lime water milky. This confirms the evolution of carbon dioxide gas in the reaction.

$C H_{3} C O O H + N a H C O_{3} \to C H_{3} C O O N a + H_{2} O + C O_{2}$

Question: 48

(a) What are hydrocarbons? Give examples.

(b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.

Solution:

(a) Hydrocarbons are compounds formed mainly from carbon and hydrogen. E.g. methane, ethene, propyne, butanol. pentanoic acid, etc.

(b) In saturated hydrocarbons, there is no double or triple bond between two carbon atoms.

In unsaturated hydrocarbons, there is at least one double or triple bond between two carbon atoms.

(c) Functional group $-$ A functional group is an atom or a group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds. Examples of functional groups includes hydroxyl group ( $-$ OH), aldehyde group ( $-$ CHO), carboxylic group ( $-$ COOH), etc.

Question: 49

Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.

Solution:

The reaction which is commonly used in the conversion of vegetable oils to fats is called hydrogenation reaction.

This reaction involves the addition of hydrogen to an unsaturated hydrocarbon to obtain saturated hydrocarbon. This reaction is carried out in the presence of a catalyst like nickel or palladium.

It can be seen that one of the two bonds between the carbon atoms breaks to accommodate hydrogen and form saturated hydrocarbon.

Question: 50

(a) Write the formula and draw electron dot structure of carbon tetrachloride.

(b) What is saponification? Write the reaction involved in this process.

Solution:

a) The chemical formula for carbon tetrachloride is $C C l_{4}$ .

(b) Saponification is the process of making soap. It involves conversion of ethyl acetate into salts of carboxylic acids and ethanol by treating them with a base.

$C H_{3} C O_{2} O H_{5} \overset{N a O H}{\to} C H_{3} C O O N a + C_{2} H_{5} O H$

Question 51

Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation of an ester with well labelled diagram.

Solution:

Activity

· Take 1ml of pure ethanol and 1ml ethanoic acid along with a few drops of concentrated sulphuric acid in a test tube.

· Warm the content in a water-bath at about $60 ° C$ for at least 5 minutes.

· Pour the content into a beaker that contains 20-50 ml of water and smell the resulting mixture.

Observation: The mixture smells sweet indicating the formation of ester.

The reaction is as follows:

$\begin{array}{l} C H_{3} C O O H + C_{2} H_{5} O H \overset{H_{2} S O_{4}}{\to} C H_{3} C O O C_{2} H_{5} + H_{2} O \\ E t h a n o i c a c i d E t h a n o l E s t e r (E t h y l e t h a n o a t e) \end{array}$

Question: 52

A compound C (molecular formula $C_{2} H_{4} O_{2}$ ) reacts with Na $-$ metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol A in the presence of an acid forms a sweet-smelling compound S (molecular formula $C_{3} H_{6} O_{2}$ ). On addition of NaOH to C, it also gives R and water. Son treatment with NaOH solution gives back R and A. Identify C, R, A, S and write down the reactions involved.

Solution:

Here, compound C (molecular formula $C_{2} H_{4} O_{2}$ ) is ethanoic acid.

R is formed when ethanoic acid reacts with sodium. Thus, R is sodium salt of ethanoic acid (sodium acetate) and gas evolved is hydrogen.

On reacting with an alcohol A, ethanoic acid forms a compound S (molecular formula $C_{3} H_{6} O_{2}$ ).

Thus, S is an ester (methyl acetate) and alcohol A is methanol.

The reactions are:

(a) $\begin{array}{l} 2 C H_{3} C O O H + 2 N a \to 2 C H_{3} C O O N a + H_{2} \\ (C) (R) \end{array}$

(b) $\begin{array}{l} C H_{3} C O O H + C H_{3} O H \overset{H_{2} S O_{4}}{\to} C H_{3} C O O C_{2} H_{5} + H_{2} O \\ (C) (A) (S) \end{array}$

(d) $\begin{array}{l} C H_{3} C O O H_{3} + N a O H \to C H_{3} C O O N a + C H_{3} O H \\ (R) (A) \end{array}$

Question: 53

Look at the figure which is given below and answer the following questions.

(a) What change would you observe in the calcium hydroxide solution taken in tube B?

(b) Write the reaction involved in test tubes A and B respectively.

(d) How can a solution of limewater be prepared in the laboratory?

Solution:

(a) Calcium hydroxide solution will turn milky when the gas evolved in the reaction is passed through it.

(b) Reactions involved in test tube A

$2 C H_{3} C O O H + N a_{2} C O_{3} \to 2 C H_{3} C O O N a + H_{2} O + C O_{2}$

Reactions involved in test tube B

$C a {(O H)}_{2} + C O_{2} \to C a C O_{3} + H_{2} O$

(c) Ethanol ( $C_{2} H_{5} O H$ ) does not react with sodium carbonate ( $N a_{2} C O_{3}$ ). Hence, a similar change is not expected.

$C_{2} H_{5} O H + N a_{2} C O_{3} \to N o c h a n g e$

(d) When calcium oxide is dissolved in water and the supernatant liquid is decanted, lime water is obtained.

Question: 54

How would you bring about the following conversions?

Name the process and write the reaction involved.

(a) Ethanol to ethene.

(b) Propanol to propanoic acid.

Solution:

(a) By the dehydration of ethanol in the presence of concentrated $H_{2} S O_{4}$ ,

$C_{2} H_{5} O H \to_{443 K}^{H o t c o n c . H_{2} S O_{4}} C H_{2} = C H_{2} + H_{2} O$

(b) By the oxidation of propanol using oxidizing agent such as alkaline $K M n O_{4}$ ,

$C H_{3} C H_{2} C H_{2} O H \to_{H e a t}^{A I k . K M n O} C H_{3} C H_{2} C O O H$

Question: 55

Draw the possible isomers of the compound with molecular formula $C_{3} H_{6} O$ and also give their electron dot structures.

Solution:

Question: 56

Explain the given reactions with the examples:

(a) Hydrogenation reaction

(b) Oxidation reaction

(d) Saponification reaction

(e) Combustion reaction

Solution:

(a) Hydrogenation reaction :

The addition of hydrogen to an unsaturated hydrocarbon to make it saturated is known as hydrogenation reaction.

Example:

$V e g e t a b l e o i l (U n s a t u r a t e d f a t) + H y d r o g e n$

$\to V e g e t a b l e g h e e (S a t u r a t e d f a t)$

(b) Oxidation reaction: The reaction which involves addition of oxygen to a reactant or removal of hydrogen from a reactant is called oxidation reaction.

Example: Methane reacts with oxygen to form carbon dioxide and water. Here methane is oxidised to carbon dioxide.

(c) Substitution reaction: When an atom or a group of atoms substitutes another atom or a group of atoms from the molecule, it is known as substitution reaction.

Example: In the presence of sunlight, chlorine is added to methane to form methyl chloride and hydrochloric acid.

$C H_{4} + C l_{2} \to C H_{3} C l + H C l$

(d) Saponification: A reaction in which an ester is hydrolysed in the presence of a base is called saponification reaction.

Example: It is used in the preparation of soap.

$C H_{3} C O O C_{2} H_{5} + N a O H \to C H_{3} C O O N a + C_{2} H_{5} O H$

(e) Combustion reaction: A reaction, in which organic compounds burn readily in air to form CO₂ and water vapour along with lot of heat, is known as combustion reaction.

Example: Methane burns in air to form carbon dioxide and water, releasing large amount of heat and light.

$C H_{4} + 2 O_{2} \to C O_{2} + 2 H_{2} O + H e a t a n d l i g h t$

Question: 57

An organic compound A on heating with concentrated $H_{2} S O_{4}$ forms a compound B which on addition of one mole of hydrogen in the presence of Ni forms a compound C. One mole of compound C on combustion forms two moles of $C O_{2}$ and 3 moles of $H_{2} O$ . Identify the compounds A, B and C and write the chemical equations of the reactions involved.

Solution:

One mole of compound C on combustion forms two moles of $C O_{2}$ and 3 moles of $H_{2} O$ . This means that the compound has at least 2 carbon atoms and 6 hydrogen atoms. Thus, the molecular formula of C is $C_{2} H_{6}$ (ethane).

Compound C, i.e. ethane, is obtained by the addition of one mole of hydrogen ( $H_{2}$ ) to compound B. Thus, compound B should be $C_{2} H_{4}$ (ethene).

Compound B, i.e. ethene, is obtained by heating the compound A with concentrated $H_{2} S O_{4}$ which shows it to be an alcohol. So compound A could be $C_{2} H_{5} O H$ (ethanol).

$\begin{array}{l} C H_{3} C H_{2} O H \overset{H o t C o n c . H_{2} S O_{4}}{\to} C_{2} H_{4} + H_{2} O \\ A B \\ C_{2} H_{4} + H_{2} \overset{N i}{\to} C_{2} H_{6} \\ B C \\ 2 C_{2} H_{6} + 7 O_{2} \to 4 C O_{2} + 6 H_{2} O + H e a t a n d l i g h t \\ C \end{array}$

A is ethanol ( $C_{2} H_{5} O H$ )

B is ethene ( $C_{2} H_{4}$ )

C is ethane ( $C_{2} H_{6}$ )