E X E R C I S E S CHAPTER 4 Carbon and its Compounds SCIENCE NCERT TEXTBOOK (CBSE) CLASS 10:

 

E X E R C I S E S

CHAPTER 4 Carbon and its Compounds


1. Ethane, with the molecular formula C₂H₆, has:

Ethane is an alkane, and each bond between carbon atoms and between carbon and hydrogen atoms is a single covalent bond.

  • The number of covalent bonds in ethane is determined by counting all the bonds formed:
    • 1 bond between the two carbon atoms
    • 6 bonds between carbon and hydrogen atoms (3 hydrogens on each carbon)

So, the total number of covalent bonds is 7.

Answer: (b) 7 covalent bonds

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

Butanone is a ketone, which has a carbonyl group (C=O) as its functional group.

Answer: (c) Ketone

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

  • This happens when the fuel is not burning completely, leading to the formation of carbon particles (soot). Incomplete combustion occurs when there is insufficient oxygen for the fuel to burn entirely.

Answer: (b) The fuel is not burning completely

4. Explain the nature of the covalent bond using the bond formation in CH₃Cl:

In CH₃Cl (methyl chloride), a covalent bond is formed by the sharing of electrons between carbon (C) and chlorine (Cl). The carbon atom shares one electron with each of the three hydrogen atoms and one electron with the chlorine atom to form single covalent bonds. This sharing of electrons allows each atom to achieve a stable electron configuration.

  • The carbon atom has 4 electrons in its outer shell and shares one with each of the 3 hydrogens and one with chlorine.
  • Chlorine has 7 electrons in its outer shell and shares one electron with carbon, completing its octet.

Thus, a covalent bond is formed when electrons are shared between atoms to achieve stable electron configurations.

5. Draw the electron dot structures for:

(a) Ethanoic acid (CH₃COOH):

  • CH₃COOH has 4 bonds: 3 between C and H atoms, 1 between C and O, and another between O and H.

The electron dot structure looks like:


   H   H   O
   |   |   ||
H—C—C—O—H
   |   |
   H   O

(b) H₂S (Hydrogen sulfide):

  • H₂S has 2 bonds between sulfur and hydrogen atoms.

The electron dot structure looks like:


        H—S—H

(c) Propanone (C₃H₆O):

  • Propanone (acetone) has 3 carbon atoms, one of which is double-bonded to oxygen (carbonyl group), and the other two are bonded to hydrogens.

The electron dot structure looks like:


  H3C—C=O
      |
      CH3

(d) F₂ (Fluorine gas):

  • F₂ has a single bond between two fluorine atoms.

The electron dot structure looks like:

      F—F

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

A homologous series is a group of organic compounds that have the same functional group and similar chemical properties, differing by a constant unit (usually a CH₂ group) in their molecular formula.

  • Example: The alkanes (methane, ethane, propane, butane) form a homologous series. They all have single bonds between carbon atoms and hydrogen atoms, and each successive member differs by one CH₂ group.

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

  • Ethanol (C₂H₅OH) is a colorless, volatile liquid with a sweet odor. It is a simple alcohol.
  • Ethanoic acid (CH₃COOH) is a colorless liquid with a sour taste and a pungent smell. It is acidic in nature.

Chemical Test:

  • Ethanoic acid turns blue litmus paper red (due to its acidic nature), while ethanol does not.
  • Ethanol does not react with sodium bicarbonate, while ethanoic acid reacts with it to produce carbon dioxide gas.

8. Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?

  • Micelles are formed when soap molecules aggregate in water. The hydrophobic tails of soap molecules face inward, and the hydrophilic heads face outward, forming a spherical structure.
  • In water, soap forms micelles because water is a polar solvent, which allows the hydrophilic heads to interact with water and the hydrophobic tails to cluster together.
  • In ethanol (a non-polar solvent), micelle formation is less likely because ethanol cannot dissolve the hydrophilic heads of the soap molecules as effectively as water can.

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

  • Carbon and its compounds (such as hydrocarbons) are used as fuels because they release a large amount of energy when they undergo combustion. This energy is harnessed for heating, electricity generation, and transportation.

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

  • Hard water contains dissolved salts like calcium and magnesium ions. When soap is added to hard water, it reacts with these ions to form insoluble compounds, which are called scum.
  • The scum formed does not clean well and is wasted soap.

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

  • Soap is basic in nature, so it will turn red litmus paper blue.

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

  • Hydrogenation is the process of adding hydrogen to a compound, typically to unsaturated fats or oils, to convert them into saturated fats.
  • Industrial application: Hydrogenation is used in the production of margarine and vegetable oils to make them solid at room temperature.

13. Which of the following hydrocarbons undergo addition reactions:

  • C₂H₆ (Ethane) – Saturated (alkane), does not undergo addition reactions.
  • C₃H₈ (Propane) – Saturated (alkane), does not undergo addition reactions.
  • C₃H₆ (Propene) – Unsaturated (alkene), undergoes addition reactions.
  • C₂H₂ (Ethene) – Unsaturated (alkene), undergoes addition reactions.
  • CH₄ (Methane) – Saturated (alkane), does not undergo addition reactions.

Answer: C₃H₆ and C₂H₂ undergo addition reactions.

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

  • Bromine water test: Unsaturated hydrocarbons (alkenes or alkynes) will decolorize bromine water, while saturated hydrocarbons (alkanes) will not react and the bromine water will remain colored.

15. Explain the mechanism of the cleaning action of soaps.

  • Soap molecules have two ends: a hydrophilic head (water-loving) and a hydrophobic tail (water-hating). When soap is added to water:
    1. The hydrophobic tails attach to grease or dirt.
    2. The hydrophilic heads point outward, interacting with water.
    3. The soap forms micelles around the dirt or grease, trapping it.
    4. The micelles are then washed away with water, removing the dirt and grease from the surface.

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