CBSE Class 10 Science Carbon And Its Compounds Worksheet Set 09

This is Worksheet Set 09 for CBSE Class 10 Science Chapter 4, Carbon and Its Compounds: a short worksheet of one-mark and two-mark questions that prints well, each with a worked answer and a Teacher's Note. It practises writing molecular formulae of homologous series members, naming functional groups, simple facts about carbon and its bonding, flames, combustion and hydrogenation.

Formulae, Names and Facts

Question 1. Write the molecular formula of first two members of homologous series having functional group-Cl. [1 mark]
Answer:
The compounds with the –Cl group are the chloroalkanes, general formula C_nH_2n+1Cl.
First two members: CH₃Cl (chloromethane) and C₂H₅Cl (chloroethane).
In simple words: Replace one hydrogen of methane and of ethane by chlorine.

Teacher's Note:
1. Start from n = 1 for the first member.
2. Each member differs by CH₂.

Question 2. Write the molecular formula of first two members of homologous series having functional group-Br. [1 mark]
Answer:
The first two members are CH₃Br (bromomethane) and C₂H₅Br (bromoethane).
In simple words: Replace one hydrogen of methane and of ethane by bromine.

Teacher's Note:
1. The general formula is C_nH_2n+1Br.
2. The functional group is –Br.

Question 3. Write the molecular formula of first two members of homologous series-having functional group -OH. [1 mark]
Answer:
The alcohol series has the general formula C_nH_2n+1OH.
First two members: CH₃OH (methanol) and C₂H₅OH (ethanol).
In simple words: The first alcohols are methanol and ethanol.

Teacher's Note:
1. Alcohols end with -ol.
2. Neighbours differ by CH₂.

Question 4. Write the molecular formula of the 2nd and 3rd members of the homologous series whose first member is methane. [1 mark]
Answer:
The series is the alkanes, C_nH_2n+2.
2nd member: ethane, C₂H₆. 3rd member: propane, C₃H₈.
In simple words: Methane, ethane, propane: the 2nd and 3rd members are C₂H₆ and C₃H₈.

Teacher's Note:
1. Count methane as the first member.
2. Add CH₂ each time.

Question 5. Write the molecular formula of the 2nd and 3rd member of the homologous series whose first member is ethene. [1 mark]
Answer:
The series is the alkenes, C_nH_2n.
2nd member: propene, C₃H₆. 3rd member: butene, C₄H₈.
In simple words: After ethene (C₂H₄) come propene (C₃H₆) and butene (C₄H₈).

Teacher's Note:
1. Add CH₂ each time.
2. Alkenes have a double bond.

Question 6. Name the period and group of carbon in the periodic table. [1 mark]
Answer:
Carbon has atomic number 6 and configuration 2, 4. It lies in period 2 and group 14.
In simple words: Two shells give period 2; four valence electrons give group 14.

Teacher's Note:
1. Period = number of shells.
2. Group 14 elements show a valency of 4.

Question 7. What is the percentage of carbon in the atmosphere ? [1 mark]
Answer:
Carbon is present in the atmosphere as carbon dioxide, and the percentage is about 0.03%.
In simple words: Only about 0.03% of air is carbon (as CO₂).

Teacher's Note:
1. It occurs as carbon dioxide.
2. Carbon is a very small part of the atmosphere.

Question 8. What is the percentage of carbon in the earth's crust? [1 mark]
Answer:
The earth's crust contains only about 0.02% carbon, in the form of minerals such as carbonates, and as coal and petroleum.
In simple words: Carbon makes up only about 0.02% of the earth's crust.

Teacher's Note:
1. Compare with 0.03% in the atmosphere.
2. Yet carbon forms millions of compounds.

Question 9. Hydrogen has one valence electron. Name the inert gas nearest to hydrogen to acquire the stable configuration by hydrogen. [1 mark]
Answer:
Hydrogen (one electron) gains one electron, by sharing, to get two electrons in its shell, like helium.
In simple words: Hydrogen aims for the duplet of helium.

Teacher's Note:
1. Hydrogen follows the duplet rule.
2. Others follow the octet rule.

Question 10. Predict the nature of bond formed between two atoms having electronic configuration of 2, 8, 6. [1 mark]
Answer:
The atoms (sulphur) have six valence electrons each and need two more. They share two electrons each, so a covalent (double) bond is formed.
In simple words: Two non-metal atoms with 6 valence electrons share two pairs of electrons.

Teacher's Note:
1. Non-metals form covalent bonds.
2. Six valence electrons need two more to reach an octet.

Question 11. What is hydrocarbon ? [1 mark]
Answer:
Compounds made up of only carbon and hydrogen are called hydrocarbons. Examples: CH₄, C₂H₆, C₅H₁₂.
In simple words: Hydrocarbons contain only C and H.

Teacher's Note:
1. They can be saturated or unsaturated.
2. Methane is the simplest hydrocarbon.

Question 12. Write the name and structure of an aldehyde with four carbon atoms in its molecule. [1 mark]
Answer:
The aldehyde with four carbon atoms is butanal: CH₃–CH₂–CH₂–CHO.
In simple words: Butanal has four carbons including the one in –CHO.

Teacher's Note:
1. Aldehydes end in -al.
2. The –CHO group is at the end of the chain.

Reactions, Flames and Functional Groups

Question 13. Name the process of converting vegetable oil to vegetable ghee. [1 mark]
Answer:
The process is hydrogenation: hydrogen is added to unsaturated vegetable oil using a nickel catalyst, giving saturated fat (ghee).
In simple words: Adding hydrogen over a nickel catalyst makes liquid oil solid.

Teacher's Note:
1. Nickel is the catalyst.
2. The double bonds are removed.

Question 14. Unsaturated hydrocarbon gives a yellow flame with lots of black smoke when burnt in air. Give reason. [1 mark]
Answer:
Unsaturated hydrocarbons contain a high percentage of carbon, and in air they burn incompletely. The unburnt carbon particles glow yellow and form black smoke (soot).
In simple words: Incomplete combustion leaves unburnt carbon, which makes the flame sooty.

Teacher's Note:
1. Saturated hydrocarbons burn with a blue flame.
2. In plenty of air an unsaturated hydrocarbon burns with less soot.

Question 15. Is combustion always accompanied by a flame ? [1 mark]
Answer:
No. Some substances, such as charcoal or coke, burn by glowing red hot without any flame, because they do not form vapours that can burn.
In simple words: Charcoal burns and glows without a flame.

Teacher's Note:
1. Flames form when gases or vapours burn.
2. Combustion is any burning in oxygen with heat.

Question 16. What is nature of combustion reaction ? [1 mark]
Answer:
Combustion is an exothermic reaction (it releases heat and often light) and it is an oxidation reaction.
In simple words: Burning gives out heat, so it is exothermic.

Teacher's Note:
1. Fuels are chosen for the heat they release.
2. Combustion needs oxygen.

Question 17. Identify the functional group in the following compounds: (i) CH₃COCH₃, (ii) HCOOH [1 mark]
Answer:
(i) CH₃COCH₃ (propanone) contains the ketone group, –CO–.
(ii) HCOOH (methanoic acid) contains the carboxylic acid group, –COOH.
In simple words: Propanone is a ketone and methanoic acid is a carboxylic acid.

Teacher's Note:
1. Ketone: C=O between two carbons.
2. Acid: –COOH.

Question 18. Write the molecular formula of alcohol which can be derived from butane. [1 mark]
Answer:
Replace one hydrogen of butane (C₄H₁₀) by –OH. The alcohol is C₄H₉OH (butanol), CH₃–CH₂–CH₂–CH₂–OH.
In simple words: Butane gives butanol, C₄H₉OH.

Teacher's Note:
1. The alcohol formula is C_nH_2n+1OH.
2. Butanol has four carbon atoms.

Question 19. Give the structural formula of alkene with three carbon atom. [1 mark]
Answer:
The alkene with three carbon atoms is propene, C₃H₆. Structural formula: CH₃–CH=CH₂, that is, H₃C–CH=CH₂.
In simple words: Propene has three carbons and one double bond.

Teacher's Note:
1. Alkenes have the general formula C_nH_2n.
2. Check that each carbon has four bonds.

Question 20. What is the dilute solution (5-8% in water) of acetic acid known as ? [1 mark]
Answer:
A 5–8% solution of acetic acid in water is known as vinegar. It is used as a preservative in pickles.
In simple words: Vinegar is dilute acetic acid.

Teacher's Note:
1. Pure acetic acid is called glacial acetic acid.
2. Vinegar is made from ethanol by oxidation.