Carbon and its Compound All Exercise and Intext Question/Answers

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1. Ethane, with the molecular formula C2H6 has

(a) 6 covalent bonds.

(b) 7 covalent bonds.

(d) 9 covalent bonds.

Answer: (b) 7 covalent bonds.

Explanation: Ethane (C2H6) has the following covalent bonds:

1 bond between the two carbon atoms
3 bonds between each carbon atom and three hydrogen atoms

So, ethane has a total of: 1(C-C bond) + 6 (C-H bonds) = 7 covalent bonds

1(C-C bond)+6(C-H bonds)=7covalent bonds

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

(a) carboxylic acid.

(b) aldehyde.

(d) alcohol.

Ans: The functional group is a ketone.

Butanone is a four-carbon compound with the functional group: O=C

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.

(d) the fuel is burning completely.

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

If the bottom of the vessel is getting blackened on the outside while cooking, it indicates incomplete combustion of the fuel, leading to the formation of soot.

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

Methane (CH4):

In methane, each carbon atom forms four covalent bonds with hydrogen atoms. Each bond involves sharing one electron from carbon and one electron from hydrogen.

C+4H → CH4

Chloromethane (CH₃CI):

In chloromethane, one hydrogen atom in methane is replaced by a chlorine atom. Chlorine also shares one electron with carbon, forming a covalent bond.

CH₃+ CI → CH₃CI

The covalent bonds are formed by sharing electrons:

3.C-H bonds
1 C-Cl bond

5. Draw the electron dot structures for (a) ethanoic acid. (b) H2 S. (c) propanone. (d) F2 .

(a) Ethanoic Acid: Imagine carbon with 4 balls (electrons), hydrogens with 1 ball each, and oxygen with 6 balls. Oxygen shares 2 with carbon (double bond), 1 with hydrogen, and the rest stay around oxygen. One hydrogen loses its ball to become H+.

(b) Hydrogen Sulfide: Sulfur has 6 balls, hydrogens have 1 each. Sulfur shares 1 ball with each hydrogen to make two single bonds.

(c) Propanone: 3 carbon atoms each share 4 balls. One oxygen shares 2 with a carbon (double bond) and keeps 4 around itself. Hydrogens each share 1 ball with a carbon.

(d) Fluorine: Each fluorine has 7 balls. They share 1 ball each to hold hands.

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

Ans: A homologous series is a group of organic compounds with a similar general formula, possessing similar chemical properties and exhibiting a gradual change in physical properties. Each member differs from the next by a CH₂ unit.

Example: Alkanes

Methane (CH₄)
Ethane (C₂H₆)
Propane (C₃H₈)
Butane (C₄H₁₀)

All alkanes have the general formula (C₂H_2n+2) and show similar chemical behavior, such as combustion and substitution reactions, while their physical properties, like boiling point and melting point, gradually change.

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

Ans: Physical Properties:

Ethanol (CH₃CH₂OH):
- Pleasant, sweet smell
- Boiling point: 78°C
- Liquid at room temperature
Ethanoic Acid (CH₃COOH):
- Sharp, vinegar-like smell
- Boiling point: 118°C
- Solidifies at 16.6°C (freezing point)

Chemical Properties:

Ethanol:
- Does not react with sodium bicarbonate (NaHCO₃)
- Neutral in litmus test (no color change)
Ethanoic Acid:
- Reacts with sodium bicarbonate to produce carbon dioxide (effervescence)
- Turns blue litmus paper red (acidic)

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?

Micelle Formation:

When soap is added to water, micelles form because soap molecules have a hydrophobic (water-repelling) tail and a hydrophilic (water-attracting) head. In water, the hydrophobic tails cluster together, while the hydrophilic heads face outward, forming a spherical structure called a micelle.

Micelle Formation in Other Solvents:

Micelles do not form in non-polar solvents like ethanol because ethanol cannot sufficiently polarize the hydrophilic heads to separate them from the hydrophobic tails. Micelle formation requires a polar solvent like water.

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

Ans: Carbon and its compounds, such as hydrocarbons, are used as fuels for several reasons:

High Energy Content: They release a significant amount of energy upon combustion.
Abundance: Carbon-based fuels are abundant and easily accessible.
Variety: They exist in various forms (solid, liquid, gas) which are suitable for different applications.
Combustion: They combust readily and produce heat, making them efficient for energy generation.

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

Ans: Scum Formation: Hard water contains calcium (Ca²⁺) and magnesium (Mg²⁺) ions. When soap (which contains sodium or potassium salts of fatty acids) is added to hard water, these ions react with the soap to form an insoluble precipitate called scum.

Reaction: 2C17H35COONa + Ca2+ →(C17H35COO)2Ca + 2Na+

The calcium or magnesium salts of fatty acids are not soluble in water, leading to the formation of scum. This reduces the effectiveness of the soap as a cleaning agent.

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

Ans: Soap is typically alkaline (basic) due to the presence of sodium or potassium salts of fatty acids.

Test Observations:

Red Litmus Paper: Turns blue, indicating the basic nature of soap.
Blue Litmus Paper: No change, as the paper is already blue and soap is basic.

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

Ans: Hydrogenation is the chemical reaction where hydrogen (𝐻2) is added to a compound, typically in the presence of a catalyst like nickel, palladium, or platinum.

Industrial Application:

Hydrogenation of Oils: Converts liquid vegetable oils (unsaturated fats) into solid or semi-solid fats (saturated fats), producing margarine and shortening. This process increases the shelf life and alters the texture of the products.

C𝑛H2𝑛+𝐻2→C𝑛H2𝑛+2

13. Which of the following hydrocarbons undergo addition reactions: C2H6 , C3H8 , C3H6 , C2H2 and CH4 .

Addition reactions typically occur with unsaturated hydrocarbons (those containing double or triple bonds). The following undergo addition reactions:

► C₂H₄ (Ethene, C₃H₆ (Propene), C₂H₂ (Ethyne)

Not undergoing addition reactions:

► C₂H₆ (Ethane), C₃H₈ (Propane), CH₄ (Methane)

These are saturated hydrocarbons with only single bonds and do not typically undergo addition reactions.

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

Bromine Water Test (Bromine water contain Br2):

Unsaturated Hydrocarbons: Decolorize bromine water (orange to colorless), indicating the presence of double or triple bonds.

R−CH=CH−R′+Br2→R−CHBr−CHBr−R′

Saturated Hydrocarbons: No change in color, indicating only single bonds are present.

R−CH2−CH3+Br2→No reaction

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

Ans: Soap Molecule Structure:

Hydrophilic Head: Attracted to water (polar).
Hydrophobic Tail: Repelled by water but attracted to grease and oils (non-polar).

Cleaning Mechanism:

Dissolution: When soap is added to water, soap molecules arrange themselves into structures called micelles.
Micelle Formation: The hydrophobic tails cluster together in the center of the micelle, trapping grease and oil, while the hydrophilic heads face outward towards the water.
Emulsification: The grease or oil trapped in the micelle is emulsified and suspended in water, breaking it into smaller droplets.
Rinsing Away: The micelles, containing the trapped grease and oil, are washed away with water, leaving the surface clean.

This process effectively removes dirt and grease from surfaces or fabrics, making soap an effective cleaning agent.

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