CBSE Class 10 Science Carbon and its Compounds VBQs Set 04

Question. In the soap micelles
(a) the ionic end of soap is on the surface of the cluster while the carbon chain is in the interior of the cluster.
(b) ionic end of soap is in the interior of the cluster and the carbon chain is out of the cluster.
(c) both ionic end and carbon chain are in the interior of the cluster.
(d) both ionic end and carbon chain are on the exterior of the cluster.
Answer: (a) Ionic end of soap is hydrophilic (water loving) whereas carbon chain of soap is hydrophobic (water hating) but attracts oil, dirt and grease.

Question. Mineral acids are stronger acids than carboxylic acids because
(i) mineral acids are completely ionised
(ii) carboxylic acids are completely ionised
(iii) mineral acids are partially ionised
(iv) carboxylic acids are partially ionised
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)
Answer: (a) (i) and (iv)

Question. Which of the following is not a straight chain hydrocarbon?
(a) \( H_3C—CH_2—CH_2—CH_2—CH_2—CH_3 \)
(b) \( H_3C—CH_2—CH_2—CH_2—CH(CH_3)—CH_3 \)
(c) \( H_2C—CH_2—CH_2—CH_2(CH_3) \)
(d) \( (CH_3)_2CH—CH_2—CH_2—CH_3 \)
Answer: (d) It is branched chain because —CH3 is attached to 2nd carbon.

Question. Draw the electron dot structure of ethyne and also draw its structural formula.
Answer: \( H:C:::C:H \) is the electron dot structure of ethyne (\( C_2H_2 \)).
\( H—C \equiv C—H \) is its structural formula.

Question. Write the names of the following compounds.
(a) \( CH_3—CH_2—CH_2—CH_2—COOH \)
(b) \( CH_3—CH_2—C \equiv C—H \)
(c) \( CH_3—CH_2—CH_2—CH_2—CH_2—CH_2—CHO \)
(d) \( CH_3—CH_2—CH_2—CH_2—CH_2—OH \)
Answer: (a) Pentanoic acid (b) 1-Butyne (c) Heptanal (d) 1-Pentanol

Question. Identify and name the functional groups present in the following compounds.
(a) \( CH_3—CH_2—CH_2—OH \)
(b) \( CH_3—CH_2—CH_2—COOH \)
(c) \( CH_3—CO—CH_2—CH_3 \)
(d) \( CH_3—CH_2—CH=CH_2 \)
Answer: (a) —OH : Alcohol
(b) —COOH : Carboxylic acid
(c) —C(=O)— : Ketone
(d) —C=C— : Alkene

Question. A compound X is formed by the reaction of a carboxylic acid \( C_2H_4O_2 \) and an alcohol in presence of a few drops of \( H_2SO_4 \). The alcohol on oxidation with alkaline \( KMnO_4 \) followed by acidification gives the same carboxylic acid as used in this reaction. Give the names and structures of (a) carboxylic acid, (b) alcohol and (c) the compound X. Also write the reaction.
Answer: (a) Carboxylic acid is ethanoic acid (\( CH_3COOH \)).
(b) Alcohol is ethanol (\( C_2H_5OH \)).
(c) ‘X’ is ethyl ethanoate (\( CH_3COOC_2H_5 \)).
Reaction: \( CH_3COOH + CH_3CH_2OH \xrightarrow{conc. H_2SO_4} CH_3COOC_2H_5 + H_2O \)
Oxidation of alcohol: \( CH_3CH_2OH + 2[O] \xrightarrow{Alkaline KMnO_4} CH_3COOH + H_2O \)

Question. Why detergents are better cleansing agents than soaps? Explain.
Answer: It is because detergents form lot of lather even with hard water. Hard water contains \( Ca^{2+} \) and \( Mg^{2+} \) ions which react with soap to form insoluble salts of calcium and magnesium called scum and soap goes waste. Detergents do not form insoluble compounds with \( Ca^{2+} \) and \( Mg^{2+} \) ions, therefore, these are more effective.

Question. Name the functional groups present in the following compounds.
(a) \( CH_3COCH_2CH_2CH_2CH_3 \)
(b) \( CH_3CH_2CH_2COOH \)
(c) \( CH_3CH_2CH_2CH_2CHO \)
(d) \( CH_3CH_2OH \)
Answer: (a) Ketone (b) Carboxylic acid (c) Aldehyde (d) Alcohol

Question. Intake of small quantity of methanol can be lethal. Comment.
Answer: Methanol is oxidised to methanal in liver. Methanal is highly reactive and good reducing agent. It causes protoplasm to coagulate. It also affects optic nerve and leads to blindness.

Question. Carbon, Group (14) element in the Periodic Table, is known to form compounds with many elements. Write an example of a compound formed with:
(a) chlorine (Group 17 of Periodic Table)
(b) oxygen (Group 16 of Periodic Table)
Answer: (a) \( CCl_4 \) (Carbon tetrachloride) (b) \( CO_2 \) (Carbon dioxide)

Question. In electron dot structure, the valence shell electrons are represented by crosses or dots. (a) The atomic number of chlorine is 17. Write its electronic configuration. (b) Draw the electron dot structure of chlorine molecule.
Answer: (a) Cl(17) Electronic configuration: K=2, L=8, M=7.
(b) Each Chlorine atom shares one electron with the other to form a single covalent bond \( :Cl : Cl: \).

Question. Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.
Answer: Carbon shows catenation to large extent as compared to silicon as well as any other element due to smaller size of carbon. C—C bond is stronger than Si—Si bond because Si is larger in size, so, it forms weaker bond.

Question. Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene.
Answer: Add bromine water. Ethane will not react. Ethene will decolourise bromine water.
Alternative Method (Combustion test): Ethane, a saturated hydrocarbon, will burn with blue flame which is non-smoky, whereas ethene, an unsaturated hydrocarbon, will burn with yellow flame which is smoky due to the presence of unburnt carbon particles.

Question. Match the reactions given in Column (A) with the names given in Column (B).
Column (A)
(a) \( CH_3OH + CH_3COOH \xrightarrow{H^+} CH_3COOCH_3 + H_2O \)
(b) \( CH_2=CH_2 + H_2 \xrightarrow{Ni} CH_3—CH_3 \)
(c) \( CH_4 + Cl_2 \xrightarrow{Sunlight} CH_3Cl + HCl \)
(d) \( CH_3COOH + NaOH \to CH_3COONa + H_2O \)
Column (B)
(i) Addition reaction
(ii) Substitution reaction
(iii) Neutralisation reaction
(iv) Esterification reaction
Answer: (a) – (iv) Esterification reaction because ester is being formed from carboxylic acid and alcohol.
(b) – (i) Addition reaction as hydrogen is being added.
(c) – (ii) Substitution reaction because hydrogen of methane is being substituted by chlorine atom.
(d) – (iii) Neutralisation reaction because acetic acid reacts with sodium hydroxide to form salt and water.

Question. Write the structural formulae of all the isomers of hexane.
Answer: 1. n-Hexane: \( CH_3—CH_2—CH_2—CH_2—CH_2—CH_3 \)
2. 2-Methylpentane: \( CH_3—CH(CH_3)—CH_2—CH_2—CH_3 \)
3. 3-Methylpentane: \( CH_3—CH_2—CH(CH_3)—CH_2—CH_3 \)
4. 2,2-Dimethylbutane: \( CH_3—C(CH_3)_2—CH_2—CH_3 \)
5. 2,3-Dimethylbutane: \( CH_3—CH(CH_3)—CH(CH_3)—CH_3 \)

Question. What is the role of metal or reagents written on arrows in the given chemical reactions?
(a) \( \text{Alkene} + H_2 \xrightarrow{Ni} \text{Alkane} \)
(b) \( CH_3COOH + CH_3CH_2OH \xrightarrow{conc. H_2SO_4} CH_3COOC_2H_5 + H_2O \)
(c) \( CH_3CH_2OH \xrightarrow[Heat]{Alkaline KMnO_4} CH_3COOH \)
Answer: (a) Ni is used as a catalyst.
(b) Conc. \( H_2SO_4 \) acts as a dehydrating agent.
(c) Alkaline \( KMnO_4 \) is an oxidising agent.

Question. (a) What are hydrocarbons? Give examples. (b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each. (c) What is a functional group? Give examples of four different functional groups.
Answer: (a) Hydrocarbons are the compounds made up of carbon and hydrogen atoms only, e.g. \( CH_4 \) (methane), \( C_2H_6 \) (ethane), \( CH_2=CH_2 \) (ethene), etc.
(b) Saturated hydrocarbons contain single covalent bonds only, e.g. methane (\( CH_4 \)) and ethane (\( C_2H_6 \)). Unsaturated hydrocarbons contain double or triple covalent bonds, e.g. ethene (\( CH_2=CH_2 \)) and ethyne (\( HC \equiv CH \)).
(c) Functional group is an atom or group of atoms or reactive part of the compound which determines chemical properties of those compounds, e.g. (i) —OH (Alcohol), (ii) —C(=O)— (Ketone), (iii) —CHO (Aldehyde), (iv) —COOH (Carboxylic acid).

Question. A compound ‘C’ (molecular formula, \( C_2H_4O_2 \)) reacts with Na metal to form a compound ‘R’ and evolves a gas which burns with a pop sound. Compound ‘C’ on treatment with an alcohol ‘A’ in presence of an acid forms a sweet smelling compound ‘S’ (molecular formula \( C_3H_6O_2 \)). On addition of NaOH to ‘C’, it also gives ‘R’ and water. ‘S’ on treatment with NaOH solution gives back ‘R’ and ‘A’. Identify ‘C’, ‘R’, ‘A’, ‘S’ and write down the reactions involved.
Answer: ‘C’ is ethanoic acid (\( CH_3COOH \)).
‘R’ is sodium ethanoate (\( CH_3COONa \)).
‘A’ is methanol (\( CH_3OH \)).
‘S’ is methyl ethanoate (\( CH_3COOCH_3 \)).
Reactions:
1. \( 2CH_3COOH + 2Na \to 2CH_3COONa + H_2 \) (gas burns with pop sound)
2. \( CH_3COOH + CH_3OH \xrightarrow{H^+} CH_3COOCH_3 + H_2O \)
3. \( CH_3COOH + NaOH \to CH_3COONa + H_2O \)
4. \( CH_3COOCH_3 + NaOH \to CH_3COONa + CH_3OH \)

Question. How would you bring about the following conversions? Name the process and write the reaction involved.
(a) Ethanol to ethene
(b) Propanol to propanoic acid
Answer: (a) Ethanol to ethene: \( CH_3CH_2OH \xrightarrow[Heat]{conc. H_2SO_4} CH_2=CH_2 + H_2O \). This is dehydration.
(b) Propanol to propanoic acid: \( CH_3CH_2CH_2OH + 2[O] \xrightarrow{Alkaline KMnO_4} CH_3CH_2COOH + H_2O \). This is oxidation.

Question. Explain the given reactions with the examples
(a) Hydrogenation reaction
(b) Oxidation reaction
(c) Substitution reaction
(d) Saponification reaction
(e) Combustion reaction
Answer: (a) Hydrogenation reaction: Addition of hydrogen to unsaturated hydrocarbons in presence of a catalyst like Ni. E.g., \( CH_2=CH_2 + H_2 \xrightarrow{Ni} CH_3—CH_3 \)
(b) Oxidation reaction: Addition of oxygen or removal of hydrogen. E.g., \( CH_3OH + [O] \xrightarrow{Alkaline KMnO_4} HCOOH + H_2O \)
(c) Substitution reaction: Replacement of an atom by another atom. E.g., \( CH_4 + Br_2 \xrightarrow{Sunlight} CH_3Br + HBr \)
(d) Saponification reaction: Reaction of an ester with a base to form salt of acid and alcohol. E.g., \( C_2H_5COOCH_3 + NaOH \to CH_3OH + C_2H_5COONa \)
(e) Combustion reaction: Burning of an organic compound in air to form \( CO_2 \), \( H_2O \), heat and light. E.g., \( 2C_2H_6 + 7O_2 \to 4CO_2 + 6H_2O + \text{Heat} + \text{Light} \)

Question. An organic compound ‘A’ on heating with conc. \( H_2SO_4 \) forms a compound B, which on addition with 1 mole of hydrogen in presence of Ni forms a compound ‘C. One mole of compound ‘C’ on combustion forms two moles of \( CO_2 \) and 3 moles of \( H_2O \). Identify the compounds A, B and C and write the chemical equation of the reactions involved.
Answer: A—Ethanol, B—Ethene, C—Ethane
1. \( CH_3CH_2OH \xrightarrow{conc. H_2SO_4} CH_2=CH_2 + H_2O \)
2. \( CH_2=CH_2 + H_2 \xrightarrow{Ni, Heat} CH_3—CH_3 \)
3. \( C_2H_6 + \frac{7}{2}O_2 \to 2CO_2 + 3H_2O \)

Question. Which of the following represents formula of a carboxylic acid?
(a) \( C_2H_4 \)
(b) \( C_4H_{10} \)
(c) \( CH_4O \)
(d) \( C_2H_4O_2 \)
Answer: (d) \( C_2H_4O_2 \)

Question. Which of the following can have structural isomers?
(a) Ethane
(b) Butane
(c) Propane
(d) Methane
Answer: (b) Butane

Question. Which of the following is general formula of alkynes?
(a) \( C_nH_{2n+2} \)
(b) \( C_nH_{2n} \)
(c) \( C_nH_{2n–2} \)
(d) \( C_nH_{2n–6} \)
Answer: (c) \( C_nH_{2n–2} \)

Question. Which of the following compound is formed when ethanoic acid reacts with ethanol in presence of conc. \( H_2SO_4 \)?
(a) \( CH_3COCH_2CH_3 \)
(b) \( CH_3COOCH_2CH_3 \)
(c) \( CH_3CH_2COOCH_3 \)
(d) \( CH_3CH_2COOCH_2CH_3 \)
Answer: (b) \( CH_3COOCH_2CH_3 \)

Direction: In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following:
(a) Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
(b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
(c) Assertion is true but the Reason is false.
(d) The statement of the Assertion is false but the Reason is true.

Question. Assertion: Unsaturated hydrocarbons decolourise bromine water.
Reason: Saturated hydrocarbons undergo substitution reaction.
(a) (a)
(b) (b)
(c) (c)
(d) (d)
Answer: (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Assertion: Ethanol reacts with Na metal to form sodium ethoxide and hydrogen gas
Reason: Ethanol does not react with \( NaHCO_3 \).
(a) (a)
(b) (b)
(c) (c)
(d) (d)
Answer: (b) The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.

Question. Write three isomers of \( C_5H_{12} \). Write their IUPAC names.
Answer: The three isomers of pentane (\( C_5H_{12} \)) are:
1. n-Pentane: \( CH_3—CH_2—CH_2—CH_2—CH_3 \)
2. 2-Methylbutane (Isopentane): \( CH_3—CH(CH_3)—CH_2—CH_3 \)
3. 2,2-Dimethylpropane (Neopentane): \( CH_3—C(CH_3)_2—CH_3 \)

Question. Write IUPAC names of following
(i) \( CH_3CH_2COOH \)
(ii) \( CH_3—CO—CH_3 \)
(iii) \( CH_3—CHO \)
(iv) \( CH_3CH_2—C \equiv CH \)
Answer: (i) Propanoic acid
(ii) Propanone
(iii) Ethanal
(iv) 1-Butyne

Question. Write chemical reactions involved:
(a) Ethanol is heated with conc. \( H_2SO_4 \) at 443 K
(b) Ethane reacts with chlorine in presence of sunlight.
(c) Ethene reacts with \( H_2O \) in presence of \( H_2SO_4 \).
Answer: (a) \( CH_3CH_2OH \xrightarrow[443 K]{conc. H_2SO_4} CH_2=CH_2 + H_2O \)
(b) \( C_2H_6 + Cl_2 \xrightarrow{sunlight} C_2H_5Cl + HCl \)
(c) \( CH_2=CH_2 + H_2O \xrightarrow{H_2SO_4} CH_3CH_2OH \)

Question. Complete the following reactions.
(a) \( C_2H_6 + O_2 \to \)
(b) \( CH_3CH_2OH \xrightarrow{KMnO_4/dil. H_2SO_4} \)
(c) \( CH_3COOH + Na_2CO_3 \to \)
Answer: (a) \( 2C_2H_6 + 7O_2 \to 4CO_2 + 6H_2O + \text{Heat} + \text{Light} \)
(b) \( CH_3CH_2OH \xrightarrow{KMnO_4/dil. H_2SO_4} CH_3COOH + H_2O \)
(c) \( 2CH_3COOH + Na_2CO_3 \to 2CH_3COONa + H_2O + CO_2 \)

Question. A compound ‘X’ (\( C_4H_8O_2 \)) on acidic hydrolysis gives ‘Y’ and ‘Z’. ‘Y’ does not react with Mg metal as well as sodium carbonate. ‘Z’ reacts with Mg metal as well as with sodium carbonate. ‘Y’ on oxidation with acidified potassium dichromate gives ‘Z’. Identify ‘X’, ‘Y’ and ‘Z’ and write reactions involved.
Answer: Compound 'X' is an ester, specifically Ethyl ethanoate (\( CH_3COOC_2H_5 \)).
'Y' is Ethanol (\( C_2H_5OH \)) because it does not react with Mg or \( Na_2CO_3 \).
'Z' is Ethanoic acid (\( CH_3COOH \)) because it reacts with Mg and \( Na_2CO_3 \).
Reactions:
1. Hydrolysis: \( CH_3COOC_2H_5 + H_2O \xrightarrow{H^+} CH_3COOH + C_2H_5OH \)
2. Oxidation of Y: \( C_2H_5OH \xrightarrow{K_2Cr_2O_7/H^+} CH_3COOH \)

Scientists have discovered that methane is green house gas which is responsible for global warming. Methane is emitted from oil wells, natural gas leakage, land fills, cattles, organic fertilizers, ponds, paddy fields filled with water, decomposition of organic matter. We have to reduce the use of fossil fuels and decrease level of \( CH_4 \) by proper waste management.

Question. Name the major component of natural gas.
Answer: Methane (\( CH_4 \)).

Question. Why is natural gas a clean fuel?
Answer: It is considered a clean fuel because it undergoes complete combustion, leaving no residue like ash, and produces fewer pollutants and greenhouse gases compared to other fossil fuels.

Question. What happens when
(i) methane undergoes combustion
(ii) methane reacts with chlorine in presence of sunlight
Or
(c) (i) Name an alcohol derived from methane.
(ii) Name an aldehyde containing one carbon atom.
Answer: (i) \( CH_4 + 2O_2 \to CO_2 + 2H_2O + \text{Heat} + \text{Light} \)
(ii) \( CH_4 + Cl_2 \xrightarrow{Sunlight} CH_3Cl + HCl \)
Or
(c) (i) Methanol
(ii) Methanal (Formaldehyde)