Class 10 Carbon and its Compounds Mock Test (CBSE)

Topics in Carbon and its Compounds

• Covalent bonding in carbon
• Versatile nature of carbon
• Saturated and unsaturated carbon compounds
• Chains, branches and rings
• Homologous series
• Nomenclature of carbon compounds
• Combustion
• Oxidation
• Addition reaction
• Substitution reaction
• Ethanol and ethanoic acid
• Soaps and detergents

Carbon and its Compounds practice questions with answers

1. Q1Multiple choice·1 mark
   During a long bus journey, a passenger keeps an open cup of dilute ethanol solution on the seat. After a few days the liquid smells sour. This change is due to:

   1. (a)addition of hydrogen to ethanol
   2. (b)evaporation of water from ethanol
   3. (c)substitution of hydrogen by chlorine in ethanol
   4. (d)oxidation of ethanol to ethanoic acid
   Show answer and step marks

   1. Correct option: (d) oxidation of ethanol to ethanoic acid+1

   Answer: (d)
2. Q2Multiple choice·1 mark
   Which of the following statements is correct regarding the structure of a soap molecule?

   1. (a)It has a hydrophobic head and a hydrophilic tail.
   2. (b)It has a hydrophilic head and a hydrophobic tail.
   3. (c)Both the head and the tail are hydrophobic.
   4. (d)Both the head and the tail are hydrophilic.
   Show answer and step marks

   1. Correct option: (b). Soap molecules consist of an ionic head that is hydrophilic (water-attracting) and a long hydrocarbon chain tail that is hydrophobic (water-repelling).+1

   Answer: (b)
3. Q3Multiple choice·1 mark
   Carbon forms covalent compounds instead of ionic compounds primarily because:

   1. (a)it easily forms $C^{4+}$ cations by losing four electrons.
   2. (b)it requires a large amount of energy to lose or gain four electrons to achieve a noble gas configuration.
   3. (c)it easily forms $C^{4-}$ anions by gaining four electrons.
   4. (d)it has six valence electrons available for ionic bonding.
   Show answer and step marks

   1. Correct option: (b). Carbon has 4 valence electrons. To form ionic bonds, it would need to lose or gain 4 electrons, which requires a prohibitive amount of energy. Therefore, it achieves stability by sharing electrons.+1

   Answer: (b)
4. Q4Short answer·2 marks
   Ethene (C$_2$H$_4$) decolourises bromine water, but a saturated hydrocarbon such as ethane does not. Explain why ethene decolourises bromine water.
   Show answer and step marks

   1. Ethene contains a carbon–carbon double bond, so it is an unsaturated compound whose double bond can open up to take part in reactions+1
   2. Bromine adds across the double bond in an addition reaction to form colourless 1,2-dibromoethane, so the reddish-brown colour of bromine water disappears+1

   Answer: Ethene has a C=C double bond that undergoes addition with bromine to form colourless 1,2-dibromoethane, so the bromine water is decolourised.
5. Q5Short answer·3 marks
   (a) Write the structural formulae of all possible chain isomers of the compound with molecular formula $C_5H_{12}$. (b) Write the IUPAC name of the isomer that has a quaternary carbon atom (a carbon bonded to four other carbon atoms).
   Show answer and step marks

   1. (a) n-Pentane: $CH_3-CH_2-CH_2-CH_2-CH_3$.+0.5
   2. (a) 2-Methylbutane: $CH_3-CH(CH_3)-CH_2-CH_3$.+0.5
   3. (a) 2,2-Dimethylpropane: $CH_3-C(CH_3)_2-CH_3$, i.e. $C(CH_3)_4$.+0.5
   4. (b) The isomer with a quaternary carbon is $C(CH_3)_4$, whose central carbon is bonded to four $CH_3$ groups.+0.5
   5. (b) Its IUPAC name is 2,2-dimethylpropane.+1

   Answer: (a) $CH_3-CH_2-CH_2-CH_2-CH_3$ (n-pentane), $CH_3-CH(CH_3)-CH_2-CH_3$ (2-methylbutane), $C(CH_3)_4$ (2,2-dimethylpropane). (b) 2,2-Dimethylpropane.
6. Q6Short answer·3 marks
   An organic compound 'A' with molecular formula $C_2H_6O$ is heated with alkaline $KMnO_4$ to form compound 'B' ($C_2H_4O_2$). (i) Identify compounds 'A' and 'B', and write the chemical equation for the conversion of A to B along with the role of alkaline $KMnO_4$ in this reaction. (ii) State the observation when compound 'B' is treated with sodium hydrogen carbonate ($NaHCO_3$). (iii) What happens if compound 'A' is heated with excess concentrated $H_2SO_4$ at $443\text{ K}$?
   Show answer and step marks

   1. (i) A is ethanol, $C_2H_5OH$.+0.5
   2. (i) B is ethanoic acid, $CH_3COOH$.+0.5
   3. (i) Equation: $CH_3CH_2OH + 2[O] \xrightarrow{\text{alkaline } KMnO_4} CH_3COOH + H_2O$.+0.5
   4. (i) Alkaline $KMnO_4$ acts as an oxidising agent.+0.5
   5. (ii) Brisk effervescence, due to carbon dioxide gas, which turns lime water milky.+0.5
   6. (iii) Ethanol is dehydrated to ethene ($C_2H_4$) and water.+0.5

   Answer: (i) A: ethanol, B: ethanoic acid; $CH_3CH_2OH + 2[O] \rightarrow CH_3COOH + H_2O$; alkaline $KMnO_4$ is the oxidising agent. (ii) Brisk effervescence of $CO_2$. (iii) Ethanol is dehydrated to ethene.

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