Unit Test (Solutions): Carbon and its Compounds | Science Class 10 PDF Download

Time: 1 Hour

M.M. 30 Marks

Attempt all Questions

• Question numbers 1 to 5 carry 1 mark each. 
• Question numbers 6 to 8 carry 2 marks each. 
• Question numbers  9 to 11 carry 3 marks each. 
• Question number 12 & 13 carry 5 marks each.

Q1. How many double bonds are there in a saturated hydrocarbon? (1 Mark)
(a) One
(b) Two
(c) Three
(d) Zero

Ans: (d)
A saturated hydrocarbon has zero double bonds.

Q2. The allotrope of carbon which is a good conductor of heat and electricity is (1 Mark)
(a) Diamond
(b) Graphite
(c) Charcoal
(d) None of these

Ans: (b)
The allotrope of carbon which is a good conductor of heat and electricity is graphite.

Q3. Which of the following will undergo an addition reaction? (1 Mark)
(a) CH₄
(b) C₃H₈
(c) C₂H₆
(d) C₂H₄

Ans: (d)
C₂H₄ is an alkene. Hence it will undergo an addition reaction.

Q4. In a diamond, each carbon atom is bonded to four other carbon atoms to form (1 Mark)
(a) A hexagonal array
(b) A rigid three-dimensional structure
(c) A structure in the shape of a football
(d) A structure of a ring

Ans: (b)
In a diamond, each carbon atom is bonded to four other carbon atoms to form a rigid three-dimensional structure.

Q5. C₃H₈ belongs to the homologous series of (1 Mark)
(a) Alkynes
(b) Alkenes
(c) Alkanes
(d) Cycloalkanes

Ans: (c)
C₃H₈ belongs to the homologous series of alkanes.

Q6. Gas is evolved when ethanol reacts with sodium. Name the gas evolved and write the balanced chemical equation of the reaction involved. (2 Marks)

Ans: Hydrogen gas is evolved when ethanol reacts with sodium.
2Na + 2CH₃CH₂OH → 2CH₃CH₂ONa + H₂

Q7. How is ethene prepared from ethanol? Give the reaction involved in it. (2 Marks)

Ans: Ethanol is heated at 443 k in excess of concentrated sulphuric acid to obtain ethene.
CH₃CH₂OH + Conc. H₂SO₄ → CH₂ = CH₂ + H₂O

Q8. Carbon, the Group (14) element in the Periodic Table, is known to form compounds with many elements. Write an example of a compound formed with (2 Marks)
(a) Chlorine (Group 17 of the periodic table)
(b) Oxygen (Group 16 of the periodic table) 

Ans:
(a) Carbon tetrachloride (CCl₄)
(b) Carbon dioxide (CO₂)

Q9. Name the functional groups present in the following compounds (3 Marks)

(a) CH₃COCH₂CH₂CH₂CH₃
(b) CH₃CH₂CH₂COOH
(c) CH₃CH₂CH₂CH₂CHO

Ans:
(a) A ketone functional group is present in the compound CH₃COCH₂CH₂CH₂CH₃.
(b) A carboxylic acid functional group is present in the compound CH₃CH₂CH₂COOH.
(c) An aldehyde functional group is present in the compound CH₃CH₂CH₂CH₂CHO.

Q10. Unsaturated hydrocarbons contain multiple bonds between the two C-atoms and show addition reactions. Give the test to distinguish ethane from ethene. (3 Marks)

Ans: The bromine water test can be used to distinguish between saturated and unsaturated hydrocarbons. Saturated compounds don’t give an additional reaction. Hence, there won’t be any change in the reaction mixture. In contrast, if an unsaturated hydrocarbon is added to bromine water, its colour will decolourise.

Saturated hydrocarbon + Br₂ → No Reaction (No Colour Change)

Unsaturated hydrocarbon + Br₂ → Reaction will occur (Decolourise)

Q11. A compound X is formed by the reaction of carboxylic acid C₂H₄O₂ and alcohol in the presence of a few drops of H₂SO₄. The alcohol on oxidation with alkaline KMnO₄ 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) compound X. Also, write the reaction. (3 Marks)

Ans: Here, the carboxylic acid is ethanoic acid, alcohol is ethanol, and compound X is ethyl ethanoate.

Structure of Ethanoic Acid

Structure of Ethanol

Structure of Ethyl Ethanoate

Reactions Involved:

CH₃COOH + CH₃CH₂COOH → CH₃COOC₂H₅ + H₂O

C₂H₅OH + Alkaline KMnO₄ → CH₃COOH

Q12. Write the structural formulae of all the isomers of hexane. (5 Marks)

Ans: There are five isomers of hexane.

Q13. Look at Figure and answer the following questions: (5 Marks) 

(a) What change would you observe in the calcium hydroxide solution taken in tube B?
(b) Write the reaction involved in test tubes A and B.
(c) Would you expect the same change if ethanol is given instead of ethanoic acid?
(d) How can a solution of lime water be prepared in the laboratory?

Ans:

(a) Calcium hydroxide solution in test tube B will become milky due to the formation of calcium carbonate.

(b) Reaction in test tube A: CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ + H₂O
Reaction in test tube B: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

(c) If ethanol is given instead of ethanoic acid, similar changes won’t be observed because ethanol does not react with sodium hydrogen carbonate.

(d) First, take distilled water in a beaker and mix calcium carbonate powder. After stirring entirely, wait till the mixture settles down. Decant the clear liquid from the beaker. This liquid is lime water.