Carbon And Its Compounds Test

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Carbon And Its Compounds Test - 3

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Weekly Quiz Competition

Question 1
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Which of the following statements about carbon and its compounds is incorrect?

A
Carbon atom has four valence electrons.

B
Each carbon atom forms four covalent bonds.

C
Allotropic forms of carbon have low melting points.

D
Compounds of carbon have low melting points.

Solution

Although covalently bonded compounds exist as molecules and have low melting points, the allotropes of carbon like diamond and graphite have very high melting points. This is because they form a 3-dimensional lattice comprising covalently bonded carbon atoms and a high amount of energy is required to break the lattice.
Hence, diamond and graphite have very high melting points.
Question 2
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The reaction which is considered the reverse of esterification is

A
combustion

B
neutralisation

C
elimination

D
saponification

Solution

Saponification or hydrolysis reaction is the reverse process of esterification.

Esterification:
Carboxylic acid + alcohol Ester + water
e.g.

CH₃COOH(aq) + C₂H₅OH CH₃COOC₂H₅ + H₂O

Soaponification:
Ester + NaOH (aq) Sodim salt of the acid + alcohol

CH₃COOC₂H₅ + NaOH(aq) CH₃COONa + C₂H₅OH
Question 3
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Which of the following compounds is not considered an organic compound?

A
Urea

B
Vinegar

C
Baking soda

D
Citric acid

Solution

Carbonates and bicarbonates of metals are not considered organic compounds.
They resemble inorganic salts in their chemical behaviour and hence, they are classified and studied as inorganic compounds.
Question 4
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Which of the following compounds has/have only double covalent bond(s) in the molecule?

a. H₂O
b. C₂H₂c. CO₂d. N₂

A
Only (a) and (b)

B
Only (b)

C
Only (c)

D
All of these

Solution

The molecule of carbon dioxide ha two double covalent bonds between carbon and oxygen atoms.
Question 5
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Which of the following options does not represent a cycloalkane?

A

B

C

D

Solution

Cycloalkanes are cyclic hydrocarbons having the general formula C_nH_2n.
These are saturated compounds and contain all single bonds.
Option (1) represents cyclopentane, option (2) represent cyclohexane and option (4) represent cyclobutane. Thus, all these are cyclohexanes.
However, option (3) is benzene, which comprises a ring of six carbon atoms and contains three double bonds. Thus, it does not represent a cycloalkane.

Question 6

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Match the trivial names of the organic compounds mentioned in the first column with their molecular formulae mentioned in the second column.

Common Name	Molecular Formula
(a) Propyl chloride	1. CH₃CI
(b) Propyl bromide	2. C₆H₁₃l
(c) Methyl chloride	3. C₃H₇CI
(d) Hexyl iodide	4. C₃H₇Br

(a) - 3, (b) - 4, (c) - 1, (d) - 2

(a) - 4, (b) - 3, (c) - 1, (d) - 2

(a) - 3, (b) - 4, (c) - 2, (d) - 1

(a) - 1, (b) - 4, (c) - 3, (d) - 2

Solution

(CH₃Cl) The common name of this molecule is methyl chloride. There is one carbon atom in this compound, so its parent name is Methane. Since one chloro group is present in this compound, so its IUPAC name is chloro-methane.

(C₆H₁₃I) The common name of this compound is Hexyl iodide. Its IUPAC name is iodo-hexane.

(C₃H₇Cl) The common name of this compound is propyl chloride.
Number of carbon atoms = 3
Functional group: Chloro
Thus, the IUPAC name is Chloro-propane.

(C₃H₇Br) The common name of this compound is Propyl bromide. Its IUPAC name is bromo-propane.

Question 7
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When ethanol is heated with conc. H₂SO₄ at 443 K, the products formed are

A
ethane and water

B
ethene and water

C
ethyne and water

D
ethanol and water

Solution

This is known as dehydration of ethanol.
Question 8
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What is the largest number of isomers that pentane (C₅H₁₂) can have?

A
4

B
3

C
2

D
6

Solution

Pentane has three chain isomers: n-Pentane, Isopentane and Neopentane.
Question 9
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Out of the following pairs of compounds, the unsaturated compounds are

A
C₂H₆ and C₄H₆

B
C₆H₁₂ and C₅H₁₂

C
C₄H₆and C₆H₁₂

D
C₂H₆ and C₄H₁₀

Solution

Alkanes are saturated hydrocarbons (C_nH_{2n + 2}), and alkenes (C_nH_2n) and alkynes (C_nH_{2n - 2}) are unsaturated hydrocarbons.
C₂H₆, C₅H₁₂ and C₄H₁₀are saturated hydrocarbons.
C₄H₆ and C₆H₁₂ are unsaturated hydrocarbons.
Question 10
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Which of the following compounds is/are unsaturated hydrocarbon(s)?

(i) Propene
(ii) Benzene
(iii) Acetylene

A
(i) and (iii)

B
(i) and (ii)

C
(iii) only

D
(i), (ii) and (iii)

Solution

All the given options are unsaturated compounds.
Question 11
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Which of the following is an aromatic compound?

A
Acetylene

B
Ethanol

C
Benzene

D
Ethanoic acid

Solution

Benzenoid compounds are generally aromatic.
Question 12
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Consider the following compounds:

(i) CH₃-CH₂-CH₂-CH₂-CH₂-CH₃
(ii) CH₃-CH=CH-CH₃
(iii)
(iv) CH₃-CC-CH₃Which of the following combinations of compounds represents isomers?

A
(i), (ii) and (iii)

B
(i) and (iii)

C
(ii) and (iv)

D
(ii) and (iii)

Solution

Each of two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties. Out of given, n-Pentane and Isopentane are chain isomers.
Question 13
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The unsaturated compounds undergo addition reactions and the saturated compounds undergo substitution reactions. Which among the following organic compounds will not undergo an addition reaction?

A
C₂H₄

B
C₂H₂

C
C₆H₆

D
CH₄

Solution

Methane is a saturated hydrocarbon and will undergo substitution reaction, not addition reaction.
Question 14
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Which of the following hydrocarbons will decolourize bromine water?

A
C₃H₈

B
C₄H₁₀

C
C₅H₁₂

D
C₅H₁₀

Solution

Unsaturated compounds undergo addition reactions with halogens.
Bromine water test is a distinction test for unsaturation, as the reddish brown colour of bromine water is discharged as bromine is added to the double bonded carbon atoms.
C₅H₁₀, pentene undergoes addition reaction with bromine and decolourizes bromine water.
Hence, option (4) is correct.
All the other options represent alkanes which are saturated hydrocarbons.
Question 15
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The conversion of ethanol to ethanoic acid in the presence of alkaline KMnO₄:

CH₃CH₂OH CH₃COOH

This reaction may be classified as

A
substitution

B
oxidation

C
displacement

D
decomposition

Solution

Alkaline KMnO₄ is a strong oxidising agent and oxidises alcohols to aldehydes, which are further oxidised to carboxylic acids.

CH₃CH₂OH CH₃CHO CH₃COOH
Question 16
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In the elimination reactions of alcohols to form alkenes, the dehydrating agent is

A
conc. H₂SO₄

B
conc. HNO₃

C
dil. HCl

D
dil. HNO₃

Solution

CH₃-CH₂-OH CH₂= CH₂+ H₂O

Here, concentrated sulphuric acid acts as both the catalyst and the dehydrating agent.
Question 17
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Why is ethanoic acid called glacial acetic acid?

A
Because it gets denatured easily

B
Because it freezes during winters in the regions with cold climate

C
Because it oxidises when it reacts with moisture

D
Because it is used as a preservative

Solution

Glacial acetic acid is the purest form of acetic acid, which freezes during winters in regions with cold climate and resembles a glacier of ice.
Question 18
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Which of the following reagents can be used to distinguish between an alcohol and a carboxylic acid?

(i) NaHCO₃
(ii) Litmus solution
(iii) Na metal

A
Only (i)

B
Only (ii)

C
Both (i) and (ii)

D
Both (ii) and (iii)

Solution

Both litmus solution and NaHCO₃ can be used to distinguish between an alcohol and a carboxylic acid.
Only carboxylic acid will turn blue litmus red.
Only carboxylic acid will give effervescence with NaHCO₃ due to the evolution of CO₂.
Example:
CH₃COOH + NaHCO₃CH₃COONa + H₂O + CO₂
However, both alcohols and carboxylic acids will produce an effervescence with Na metal due to the evolution of H₂ gas; hence, this reaction will not help to identify the compound.
Question 19
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Which of the following statements is false about soap?

A
Soap solution in water is basic and can be used to wash all kinds of fabric.

B
Soap forms lather only in soft water.

C
Soap is a metallic salt of higher fatty acids.

D
Mixture of soap in water is a true solution.

Solution

Mixture of soap in water is a colloid as the soap micelles formed are in the colloidal range ( 1 nm to 10³ nm) and behave as colloidal particles.
Hence, option (4) is incorrect, regarding a mixture of soap in water.

All other statements are correct with reference to soap.
Soap is a sodium salt of higher carboxylic acids; it is a basic salt and its solution will have a pH more than 7.
Soap produces lather with soft water but not with hard water, because the corresponding calcium and magnesium salts are insoluble in water.
Question 20
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Which of the following represents saponification reaction?

A
CH₃COONa + NaOH CH₄+ Na₂CO₃

B
CH₃COOH + C₂H₅OH CH₃COOC₂H₅ + H₂O

C
2CH₃COOH + 2Na 2CH₃COONa + H₂

D
CH₃COOC₂H₅+ NaOH CH₃COONa + C₂H₅OH

Solution

Saponification reaction is the reverse of esterification and the esters undergo alkaline hydrolysis to produce sodium salts of the acid (soap) and alcohol.