Carbon & its Compounds CBQs — CBSE Class 10 (2027) with step-wise solutions

Sample Carbon & its Compounds CBQs

1. Question 1MCQ1 mark
   On undergoing complete combustion in an adequate supply of oxygen, an organic compound produces only carbon dioxide and water vapour as the products. Based on this information, which of the following homologous series could the compound belong to? P) alkanes Q) alcohols R) aldehydes
   • only P
   • only P or Q
   • only Q or R
   • any - P, Q or R
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   1. [1 mark] Correct option: (4) any - P, Q or R. Alkanes, alcohols and aldehydes all contain only carbon, hydrogen and (in the last two) oxygen, so complete combustion of any of them can give only carbon dioxide and water vapour. The information therefore does not narrow the series down.

   Answer: any - P, Q or R

2. Question 2Assertion-Reason1 mark
   Two statements are given - one labelled Assertion (A) and the other labelled Reason (R). Read the statements carefully and choose the option that correctly describes statements A and R. Assertion (A): Vegetable oils are healthier than animal fats. Reason (R): Vegetable oils generally have long unsaturated carbon chains while animal fats have saturated carbon chains.
   • Both A and R are true and R is the correct explanation for A.
   • Both A and R are true and R is not the correct explanation for A.
   • A is true but R is false.
   • A is false but R is true.
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   1. [1 mark] Correct option: (1) Both A and R are true and R is the correct explanation for A. Vegetable oils are indeed considered healthier, and the reason given - that they contain unsaturated chains while animal fats are saturated - is exactly why.

   Answer: Both A and R are true and R is the correct explanation for A.

3. Question 3Short answer3 marks
   A piece of sodium metal is added to excess ethanol and the gas produced is collected. The volume of gas is recorded every 10 s: 0 s→0, 10 s→20, 20 s→40, 30 s→58, 40 s→72, 50 s→80, 60 s→80 (cm3). Describe how the rate of reaction changed during the reaction, and suggest why it changed in this way.
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   1. [1 mark] At first the gas is produced quickly (about 20 cm3 every 10 s), but the rate then decreases (smaller volume increases between readings).
   2. [1 mark] The reaction finally stops, shown by the volume staying constant at 80 cm3 (from 50 s to 60 s).
   3. [1 mark] This is because the sodium is being used up, so less sodium remains to react and the rate falls to zero when it is all consumed.

   Answer: The rate decreased and then stopped (gas volume levelled at 80 cm3) because the sodium was used up.

4. Question 4Case study4 marks
   Home-made vinegar is produced from wine. The wine is taken in a clean glass jar and shaken well to aerate it. Some water is added to the jar and then it is kept undisturbed in a dark place at room temperature to undergo fermentation. After 3-4 weeks, the vinegar would be ready to use. (a) Name the functional groups of the MAIN organic compounds present in wine and vinegar. (b) Based on the atoms getting added/removed when wine is converted to vinegar, name the type of reaction that happens. (c) Name any chemical reagent that would be used for the same reaction if it is carried out in the laboratory.
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   1. [2 marks] (a) wine - hydroxyl / alcohol / -OH; vinegar - carboxyl / carboxylic acid / -COOH.
   2. [1 mark] (b) oxidation
   3. [1 mark] (c) any oxidising agent such as: potassium permanganate / KMnO₄; potassium dichromate / K₂Cr₂O₇.

   Answer: (a) hydroxyl in wine, carboxyl in vinegar; (b) oxidation; (c) alkaline KMnO₄ or acidified K₂Cr₂O₇.

5. Question 5Long answer5 marks
   A laboratory assistant in Hyderabad found two cylinders of hydrocarbon gases labelled only with their molecular formulae: X = C4H10 and Y = C4H8. Both compounds have open (straight) chains of carbon atoms. (a) Which of the two is saturated and which is unsaturated? Justify using their general formulae. (b) Predict the type of flame each gas gives when burnt in air. (c) When Y is passed with hydrogen over heated nickel, it is converted into X. Name this type of reaction and write the chemical equation. (d) What is the role of nickel in the reaction in (c)? (e) Write the balanced chemical equation for the complete combustion of X in air.
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   1. [1 mark] (a) X = C4H10 fits CnH2n+2 (alkane), so it has only single bonds and is saturated; Y = C4H8 fits CnH2n (alkene), so it has a carbon–carbon double bond and is unsaturated.
   2. [1 mark] (b) X (saturated) burns with a clean blue flame; Y (unsaturated) burns with a yellow flame with a lot of black smoke (sooty flame).
   3. [1 mark] (c) Addition reaction (hydrogenation): C4H8 + H2 → C4H10, in the presence of a nickel catalyst on heating.
   4. [1 mark] (d) Nickel acts as a catalyst: it makes the reaction take place (at a faster rate) without itself being used up in the reaction.
   5. [1 mark] (e) 2C4H10 + 13O2 → 8CO2 + 10H2O + heat and light.

   Answer: (a) X saturated, Y unsaturated. (b) X blue; Y sooty yellow. (c) Addition/hydrogenation: C4H8 + H2 → C4H10. (d) Catalyst. (e) 2C4H10 + 13O2 → 8CO2 + 10H2O.

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