Question Bank — Carbon and its Compounds

Section A — MCQs (10 questions, 1 mark each)

1. Which of the following correctly represents the electron dot structure of a molecule of chlorine?
(a) Two chlorine atoms sharing one pair of electrons
(b) Two chlorine atoms sharing two pairs of electrons
(c) Two chlorine atoms sharing three pairs of electrons
(d) Chlorine atom losing one electron to another chlorine atom

2. The general formula of the homologous series of alkenes is
(a) CₙH₂ₙ₊₂
(b) CₙH₂ₙ
(c) CₙH₂ₙ₋₂
(d) CₙH₂ₙ₊₁

3. Assertion (A): Carbon forms a large number of compounds due to its property of catenation.
Reason (R): Carbon has a valency of four and forms strong covalent bonds with other carbon atoms.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

4. Ethanol reacts with sodium to produce
(a) sodium ethoxide and hydrogen
(b) sodium ethanoate and water
(c) ethene and water
(d) ethanoic acid and hydrogen

5. Assertion (A): Unsaturated hydrocarbons give a yellow flame with black smoke on burning.
Reason (R): Unsaturated hydrocarbons undergo incomplete combustion in limited supply of air.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

6. The functional group present in propanone is
(a) –OH
(b) –CHO
(c) >C=O
(d) –COOH

7. Which of the following will give a clean blue flame on burning?
(a) Ethanol in limited air supply
(b) Methane in sufficient air supply
(c) Ethene in limited air supply
(d) Kerosene with blocked air holes

8. The number of covalent bonds in ethyne (C₂H₂) is
(a) 2
(b) 3
(c) 4
(d) 6

9. Soap forms micelles in water because
(a) the hydrophobic end interacts with water
(b) the hydrophilic end interacts with oil
(c) the hydrophobic end interacts with oil and hydrophilic end with water
(d) both ends are hydrophilic

10. Which allotrope of carbon is a good conductor of electricity?
(a) Diamond
(b) Graphite
(c) Fullerene
(d) None of these

Section B — Very Short Answer (6 questions, 2 marks each)

1. Define catenation. Give one example of a compound showing this property in carbon.

2. Write the electron dot structure of ethene (C₂H₄).

3. What is a homologous series? Give one example from alkanes.

4. Why do carbon compounds generally have low melting and boiling points?

5. Distinguish between a substitution reaction and an addition reaction with one example each from carbon compounds.

6. What happens when ethanol is heated at 443 K with excess concentrated sulphuric acid? Write the chemical equation.

Section C — Short Answer (5 questions, 3 marks each)

1. Explain the formation of a covalent bond in methane (CH₄) with the help of an electron dot structure. Why are such compounds poor conductors of electricity?

2. What are structural isomers? Draw the two possible structures of butane (C₄H₁₀).

3. Write the balanced chemical equations for:
(i) Combustion of ethane
(ii) Reaction of ethanoic acid with sodium carbonate
(iii) Oxidation of ethanol using alkaline KMnO₄

4. How does the presence of a functional group affect the properties of carbon compounds? Illustrate with the example of the –OH group.

5. Why is ethanoic acid called a weak acid? Compare its reaction with litmus and sodium hydroxide with that of a strong mineral acid.

Section D — Long Answer (3 questions, 5 marks each)

1. What are soaps and detergents? Explain the mechanism of cleaning action of soap with the help of a labelled diagram of micelle formation. Why do soaps not work effectively in hard water while detergents do? (Diagram-based)

2. Describe the versatile nature of carbon. Explain the two characteristic properties (tetravalency and catenation) that lead to the formation of a large number of carbon compounds. Give examples of straight chain, branched chain and cyclic compounds.

3. Write the chemical equations and observations for the following reactions of ethanol:
(i) With sodium
(ii) Dehydration
(iii) Esterification with ethanoic acid
Also state two uses of ethanol.

Section E — Case/Source-Based (2 questions, 4 marks each)

Case 1

A student performs an activity by burning different carbon compounds on a spatula. He observes that methane gives a clean blue flame while ethene produces a yellow flame with black smoke. When the air supply is reduced, even methane gives a sooty flame. He also notes that coal and petroleum contain sulphur and nitrogen which form harmful oxides on burning.

Sub-questions:
(a) Why does ethene produce black smoke while methane does not? (1)
(b) What happens when the air supply is limited even for saturated hydrocarbons? (1)
(c) Name the major pollutants formed from combustion of coal and petroleum. (1)
(d) Suggest one way to obtain a clean blue flame in a kitchen stove. (1)

Case 2

A laboratory assistant prepares a 5–8% solution of ethanoic acid in water and uses it as vinegar for preservation. He also demonstrates the reaction of glacial ethanoic acid with ethanol in the presence of concentrated sulphuric acid, producing a sweet-smelling compound. On adding NaOH to this compound, alcohol and a sodium salt are regenerated.

Sub-questions:
(a) What is the common name of the 5–8% ethanoic acid solution? (1)
(b) Name the sweet-smelling compound formed and the type of reaction. (1)
(c) Write the chemical equation for the reaction of the ester with NaOH. (1)
(d) What is this reaction with NaOH commonly called and why is it important? (1)

Section F — HOTS and Application (4 questions, 3 marks each)

1. Predict-and-justify: What would happen if carbon did not exhibit catenation? How would this affect the number of carbon compounds existing in nature? Justify your answer.

2. Analyse an unexpected observation: In an experiment, a student burns ethanol in a burner and observes a clean flame, but when the same ethanol is burnt with limited air supply, a black deposit appears on a metal plate above the flame. Analyse this observation and explain the reason.

3. Apply to an unfamiliar real-life situation: In cold climates, pure ethanoic acid often solidifies in winter. A chemist uses this property to identify a sample. How can this property be used to distinguish pure ethanoic acid from ethanol? Explain.

4. Compare two situations: Two hydrocarbons having the same number of carbon atoms are burnt separately. One gives a clean flame while the other gives a yellow sooty flame. Compare the two situations and justify which one is saturated and which is unsaturated, giving reasons.