Chapter - 4: Carbon and Its Compounds
Textual Questions and Answers:
1. What would be the electron dot structure of carbon dioxide which has the formula CO₂?
Answer:
Carbon dioxide is a covalent molecule consisting of three atoms, where a carbon atom is bonded to two oxygen atoms. Both carbon and oxygen have p orbitals that can interact due to their symmetrical compatibility. According to the valence bond theory, carbon forms four bonds, while oxygen forms two.
2. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? [Hint: the eight atoms of sulphur are joined together in the form of a ring]?
Answer: The atomic number of sulfur is 16, and its electronic configuration is 2,8,6. The sulfur atom has six valence electrons. S₈ is the chemical formula for a sulfur molecule, and each sulfur atom is bonded to identical atoms on each side by single covalent bonds, completing its octet.
Textual Questions and Answers:
1. How many structural isomers can you draw for pentane?
Answer: Three structural isomers of pentane are:
- n-Pentane
- Iso-Pentane
- Neopentane
2. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Answer: (i) Catenation - The ability of carbon atoms to form long chains and rings by bonding with other carbon atoms.
(ii) Tetravalency - Carbon has four valence electrons, allowing it to form stable covalent bonds with various elements, including hydrogen, oxygen, and nitrogen.
3. What will be the formula and electron dot structure of cyclopentane?
Answer: The chemical formula for cyclopentane is C₅H₁₀, and it is a cyclic molecule.
4. Draw the structure for the following compounds: (i) Ethanoic acid (ii) Bromopentane (iii) Butanone (iv) Hexanal
Answer: (i) Ethanoic acid - CH₃COOH
(ii) Bromopentane - C₅H₁₁Br
(iii) Butanone - CH₃COCH₂CH₃
(iv) Hexanal - C₆H₁₂O
5. How would you name the following compounds?
Answer:
(i) Bromoethane
(ii) Methanal.
(iii) Hexyne.
Textual Questions and Answers:
1. Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Answer: The conversion of ethanol to ethanoic acid is an oxidation reaction because oxygen is added to ethanol by oxidizing agents like alkaline potassium permanganate or acidified potassium dichromate.
2. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Answer: The oxygen-ethyne flame is extremely hot and produces a very high temperature, which is used for welding metals. A mixture of ethyne and air is not used because ethyne burns incompletely in air, producing a sooty flame that is not hot enough for welding.
Textual Questions and Answers:
1. How would you distinguish experimentally between an alcohol and a carboxylic acid?
Answer: Carboxylic acids react with sodium carbonate to produce carbon dioxide gas, which turns lime water milky, whereas alcohols do not react with sodium carbonate.
Reaction: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
2. What are oxidising agent?
Answer: Oxidising Agent.
Page -76
1. Would able to check if water is hard by using a no. detergent?
Answer: Detergents cannot be used to check the hardness of the water, as they lather easily in both soft and hard water. However, the hardness of water can be detected using soaps, as soaps don't lather easily in hard water.
2. People use a variety of methods to wash cloths, usually after adding the soap, they 'beat' the cloths on a stone, or beat it with a paddle, scrub with a brush or the mixture is agitated in a washing machine why is agitation necessary to get clean clothes?
Answer: It is necessary to agitate to get clean clothes because the soap micelles which entrap oily or greasy particles on the surface of dirty cloth have to be removed from its surface. When the cloth washed in soap solution is agitated or beaten, the micelles containing any or greasy dirt particles get removed from the surface of dirty cloth and go into water. And the dirty cloth gets cleaned.
Chapter - 4: Carbon and Its Compounds
Exercises:
1. Ethane, with the molecular formula C₂H₆, has how many covalent bonds?
(a) 6 covalent bonds
(b) 7 covalent bonds
(c) 8 covalent bonds
(d) 9 covalent bonds
Answer: (b) 7 covalent bonds
2. Butane is a four-carbon compound with which functional group?
(a) Carboxylic 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, what does it indicate?
(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 CH₃Cl.
Answer: Covalent bonds form by sharing electrons so that the atoms complete their outermost shells. In CH₃Cl, carbon forms four covalent bonds: three with hydrogen atoms and one with a chlorine atom, sharing electrons to achieve stability.
5. Draw the electron dot structures for:
(a) Ethanoic acid
(b) H₂S
(c) Propanone
(d) F₂
Answer: (a) Ethanoic acid: CH₃COOH
(b) H₂S: H-S-H
(c) Propanone: CH₃COCH₃
(d) F₂: F-F
6. What is a homologous series? Explain with an example.
Answer: A homologous series is a group of organic compounds with the same general formula and similar chemical properties, where each successive compound differs by a CH₂ group. Example: Alkanes (Methane - CH₄, Ethane - C₂H₆, Propane - C₃H₈).
7. How can ethanol and ethanoic acid be differentiated on the basics of their physical and chemical properties?
Answer:
(a) Ethanol has a pleasant smell, while ethanoic acid has a vinegar-like odor.
(b) Ethanol is neutral, while ethanoic acid turns blue litmus red.
(c) Ethanol does not react with sodium bicarbonate, while ethanoic acid produces CO₂.
8. Why does micelle formation take place when soap add to water? Will a micelle be formed in other solvents such as ethanol also?
Answer: Micelles form because soap molecules have a hydrophobic tail and a hydrophilic head, which arrange themselves in water. In ethanol, micelles do not form because ethanol is a non-polar solvent.
9. Why are carbon and its compounds used as fuels for most applications?
Answer: Carbon compounds release a large amount of heat energy when burned, making them efficient fuels.
10. Explain the formation of scum when hard water is treated with soap.
Answer: Hard water contains calcium and magnesium ions, which react with soap to form insoluble scum.
11. What change will you observe if you test soap with litmus paper?
Answer: Soap turns red litmus paper blue, indicating that it is basic.
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. It is used in the production of vegetable ghee from oils.
13. Which of the following hydrocarbons undergo addition reactions?
(a) C₂H₆
(b) C₃H₈
(c) C₃H₆
(d) C₂H₂
Answer: (c) C₃H₆ and (d) C₂H₂ undergo addition reactions.
14. Give a test that can be used to differentiate chemically between butter and cooking oil.
Answer: When bromine water is added to cooking oil, its color disappears, indicating unsaturation. Butter does not react.
15. Explain the mechanism of the cleaning action of soap.
Answer: Mechanism of the cleaning action of soap:When soap is dissolved in water, it forms a colloidal suspension, creating spherical structures called micelles. A soap molecule has two parts:
The hydrophobic (non-polar) tail: This part is water-repelling and is attracted to grease or oil.
The hydrophilic (polar) head: This part is water-attracting and faces outward towards the water.
In micelles, the hydrocarbon tails cluster inward around the grease or oil, while the ionic heads remain on the outside, interacting with water. This forms an emulsion, allowing the grease or dirt to be lifted and washed away with water.
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