10th Carbon and Its Compound NCERT Solution

Answers to Science Questions

1. Ethane, with the molecular formula C₂H₆, has

(a) 6 covalent bonds.

(b) 7 covalent bonds.

(c) 8 covalent bonds.

(d) 9 covalent bonds.

Answer: (a) 6 covalent bonds.

2. Butanone is a four-carbon compound with the functional group

(a) carboxyl acid.

(b) aldehyde.

(c) ketone.

(d) alcohol.

Answer: (c) ketone.

3. While cooking, if the bottom of the vessel is getting blackened on the outside, it means that

(a) the food is not cooked completely.

(b) the fuel is not burning completely.

(c) the fuel is wet.

(d) the fuel is burning completely.

Answer: (b) the fuel is not burning completely.

4. Explain the nature of the covalent bond using the bond formation in CH₄.

Answer: In CH₄ (methane), a covalent bond forms when carbon shares its four valence electrons with four hydrogen atoms. Each carbon-hydrogen bond is created by the sharing of electron pairs, resulting in a stable molecule.

5. Draw the electron dot structures for

(a) ethanoic acid.

Answer: (a) [Imagine a dot structure with CH₃-C(=O)-OH, where C shares electrons with H, O, and another O bonded to H.]

(b) H₂S.

Answer: (b) [Imagine a dot structure with H-S-H, where S shares two electrons with two H atoms.]

(c) propanone.

Answer: (c) [Imagine a dot structure with CH₃-C(=O)-CH₃, where C shares electrons with O and two CH₃ groups.]

(d) F₂.

Answer: (d) [Imagine a dot structure with F-F, where two F atoms share one pair of electrons.]

6. What is an homologous series? Explain with an example.

Answer: An homologous series is a group of organic compounds with similar structures and properties, differing by a -CH₂- unit. Example: Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈).

7. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?

Answer: Ethanol is a liquid with a pleasant smell, burns with a blue flame, and does not react with sodium bicarbonate. Ethanoic acid has a vinegar-like smell, turns blue litmus red, and reacts with sodium bicarbonate to release CO₂ gas.

8. Why do micelles form when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

Answer: Micelles form when soap is added to water because the hydrophobic tails group together and the hydrophilic heads face outward, surrounding dirt. Micelles are less likely to form in ethanol as it is not a polar solvent like water.

9. Why are carbon and its compounds used as fuels for most applications?

Answer: Carbon and its compounds are used as fuels because they burn to release a large amount of heat energy due to the strong bonds in their molecules.

10. Explain the formation of scum when hard water is treated with soap.

Answer: Scum forms when hard water, containing calcium and magnesium ions, reacts with soap to form insoluble calcium and magnesium salts of fatty acids.

11. What change will you observe if you test soap with litmus paper (red and blue)?

Answer: Soap will turn red litmus paper blue, indicating it is basic, and have no effect on blue litmus paper.

12. What is hydrogenation? What is its industrial application?

Answer: Hydrogenation is the addition of hydrogen to unsaturated hydrocarbons in the presence of a catalyst. Its industrial application is in making vegetable ghee from oils.

13. Which of the following hydrocarbons undergo addition reactions:

C₂H₆, C₃H₈, C₃H₆, C₂H₂, and CH₄.

Answer: C₃H₆ and C₂H₂ undergo addition reactions as they are unsaturated hydrocarbons with double or triple bonds.

14. Give a test that can be used to differentiate between saturated and unsaturated hydrocarbons.

Answer: Add bromine water to the hydrocarbon. Saturated hydrocarbons will not decolorize bromine water, while unsaturated hydrocarbons will turn it from brown to colorless.

15. Explain the mechanism of the cleansing action of soap.

Answer: Soap works by forming micelles around dirt particles. The hydrophobic tails trap the dirt, and the hydrophilic heads interact with water, allowing the dirt to be rinsed away.