Q1. Ethane, with the molecular formula C₂H₆ has
(a) 6 covalent bonds
(b) 7 covalent bonds
(c) 8 covalent bonds
(d) 9 covalent bonds
Answer:
(b) 7 covalent bonds.

Q2. Butanone is a four-carbon compound with the functional group
(a) carboxylic acid
(b) aldehyde
(c) ketone
(d) alcohol
Answer:
(c) Ketone.

Q3. 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.

Q4. Explain the nature of the covalent bond using the bond formation in CH₃Cl.
Answer:
Covalent bond is formed by sharing of electrons so that the combining atoms complete their outermost shell.

In CH₃Cl : C = 6, H = 1 and Cl = 17 And their electronic configuration is C – 2,4, H – 1 and Cl – 2, 8, 7

Three hydrogen atoms complete their shells by sharing three electrons (one electron each) of carbon atom.
Chlorine completes its outer shell by sharing its one out of seven electrons with one electron of carbon atom.
Thus carbon atom shares all its four electrons with three hydrogen atoms and one of chlorine atom and completes its outermost shell and single covalent bonds are formed in CH₃Cl.

Q5. Draw the electron dot structures for
(a) ethanoic acid
(b) propanone
(c) H₂S
(d) F₂.
Answer:

Q6. What is a homologous series ? Explain with an example.

Answer:
A homologous series is a group of organic compounds that have the same functional group and similar chemical properties. Each compound in the series differs from the next by a –CH₂– group. For example, in the alkane series, methane (CH₄), ethane (C₂H₆), and propane (C₃H₈) all follow the same pattern and show similar reactions.

Main Features of a Homologous Series:

1. All compounds follow the same general formula (e.g., alkanes: CₙH₂ₙ₊₂).

2. Each member differs from the next by –CH₂– (one carbon and two hydrogen atoms).

3. The molecular mass increases by 14 u for each step.

4. They show similar chemical properties.

5. Their physical properties (like boiling point) change gradually with molecular size.

Q7. How can ethanol and ethanoic acid he differentiated on the basis of their physical and chemical properties ?
Answer:
Difference on the basis of physical properties

Difference on the basis of chemical properties

Q8. Why does micelle formation take place when soap is added to water ? Will a micell be formed in other solvents such as ethanol also ?
Answer:
Micelle formation takes place when soap is added to water because the hydrocarbon chains of soap molecules are hydrophobic (water repelling) which are insoluble in water, but the ionic ends of soap molecules are hydrophilic (water attracting) and hence soluble in water.
Such micelle formation will not be possible in other solvents like ethanol in which sodium salt of fatty acids do not dissolve.

Q9. Why are carbon and its compounds used as fuels for most applications ?
Answer:
Carbon and its compounds give a large amount of heat per unit weight and are therefore, used as fuels for most applications.

Q10. Explain the formation of scum when hard water is treated with soap.
Answer:
Hard water contains salts of calcium and magnesium. Calcium and magnesium on reacting with soap form insoluble precipitate called scum. The scum formation lessens the cleansing property of soaps in hard water.

Q11. What change will you observe if you test soap with litmus paper (red and blue)?
Answer:
Red litmus will turn blue because soap is alkaline in nature. Blue litmus remains blue in soap solution.

Q12. What is hydrogenation ? What is its industrial application ?
Answer:
The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydro-carbon is called hydrogenation. The process of hydrogenation takes place in the presence of nickel (Ni) or palladium (Pd) metals as catalyst.

Application : The process of hydrogenation has an important industrial application. It is used to prepare vegetable ghee from vegetable oils.

Q13. Which of the following hydrocarbons undergo addition reactions :
C₂H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄
Answer:
Addition reactions take place only in unsaturated hydrocarbons. So addition reaction take place only in C₃H₆ and C₂H₂.

Q14. Give a test that can be used to differentiate chemically between butter and cooking oil.

To chemically differentiate between butter (a saturated fat) and cooking oil (an unsaturated fat), the Bromine water test can be used.

Test: Bromine Water Test

• Procedure:
  Add a few drops of bromine water to separate samples of butter and cooking oil and shake them well.

• Observation:

  • In cooking oil, the reddish-brown color of bromine water disappears due to the presence of unsaturated carbon–carbon double bonds (C=C), which react with bromine.

  • In butter, the reddish-brown color remains unchanged, indicating it is saturated and does not react with bromine water.

Conclusion:

Cooking oil decolorizes bromine water, while butter does not — thus, the bromine water test helps to distinguish between the two.

Q15. Explain the mechanism of the cleaning action of soaps.
Answer:
Soaps clean by removing oily and greasy dirt from surfaces using a process called emulsification. A soap molecule has two ends: a hydrophobic tail (repels water, attracts oil) and a hydrophilic head (attracts water). When soap is added to water and applied to an oily surface, the hydrophobic tails stick to the oil or grease, while the hydrophilic heads remain in the water. This forms tiny bubble-like structures called micelles, where the oil is trapped inside. When we rinse with water, the micelles get washed away, taking the dirt and oil along with them — leaving the surface clean.