CBSE Class 10 Science Carbon and its compound Sure Shot Questions Set 01

CBSE Class 10 Science Chapter 4 Carbon and its compound MCQs

Question. Which of the following organic compounds does not have the same chemical properties as methanol?
(a) C₂H₆O
(b) C₅H₁₀O
(c) C₄H₁₀O
(d) C₇H₁₆O
Answer. B

Question. Which of the following is correct about the structure of diamond?
(a) Carbon atoms are held together by single covalent bonds.
(b) Electrons move freely through the structure.
(c) Layers of atoms slide easily over each other.
(d) Carbon atoms conduct electricity in the molten state.
Answer. A

Question. Z has the same boiling point as n-butane.
(a) 1, 2 and 3
(b) 2 and 4
(c) 1 and 4
(d) 1, 3 and 4
Answer. A

Question. How many structural isomers are possible for pentane (C₅H₁₂)?
(a) 1
(b) 4
(c) 2
(d) 3
Answer. D

Question. In C₆H₁₄ the number of possible isomers is
(a) 3
(b) 6
(c) 4
(d) 5
Answer. D

Question. __________ is widely used as a fuel and is a major component of bio-gas and CNG. It is also one of the simplest compounds formed by carbon.
(a) Ethane
(b) Propane
(c) Carbon dioxide
(d) Methane
Answer. D

ASSIGNMENT QUESTIONS SET - 1
CHAPTER - 4
CARBON AND ITS COMPOUND

1. Which of the following is not a saturated hydrocarbon ?
i) Cyclohexane.
ii) Benzene.
iii) Butane
iv) isobutene

Answer: ii) Benzene.

1. Cyclohexane (C₆H₁₂) and butane (C₄H₁₀) have only single bonds, so they are saturated.
2. Benzene (C₆H₆) has alternate double bonds in its ring, so it is unsaturated.
3. Hence, the correct option is ii) Benzene.

Teacher's Note:
a) Isobutene (an alkene) is also unsaturated; the saturated hydrocarbon intended here is isobutane, as printed in Q16.
b) The intended answer is benzene, the ring compound with double bonds.

2. The bond between two identical non metallic atom has a pair of electron ?
i) un equally shared between two atoms.
ii) Transferred completely from one atom to another.
iii) With identical spins
iv) Unequally shared between them.

Answer: i) un equally shared between two atoms.

1. Two identical non-metal atoms attract the shared electrons equally, so the pair is shared equally.
2. The printed option i) is a misprint of "equally shared between two atoms"; options ii) and iv) are wrong, because transfer happens in ionic bonds and unequal sharing between unlike atoms.
3. Hence, the correct option is i), read as "equally shared between two atoms".

Teacher's Note:
a) Identical atoms have the same electronegativity, so the shared pair lies midway.
b) The printed "un equally" contradicts this; the correct idea is equal sharing, as in Q17.

3. Covalent compounds are generally
i) Soluble in water
ii) Insoluble in water
iii) Ionize in water
iv) Hydrolyse in water

Answer: ii) Insoluble in water

1. Covalent compounds are made of neutral molecules, not ions.
2. They are generally insoluble in water and dissolve in organic solvents.
3. Hence, the correct option is ii) Insoluble in water.

Teacher's Note:
a) Covalent compounds do not ionise, so they are poor conductors of electricity.
b) Ionic compounds are the ones that dissolve in water and ionise.

4. Propane with the molecular formula C₃H₈ has
i) 7covalent bonds
ii) 8 covalent bonds
iii) 9 covalent bonds
iv) 10 Covalent bonds.

Answer: iv) 10 Covalent bonds.

1. Propane is CH₃-CH₂-CH₃.
2. Number of C-C bonds = 2 and number of C-H bonds = 8.
3. Total covalent bonds = 2 + 8 = 10.
4. Hence, the correct option is iv) 10 Covalent bonds.

Teacher's Note:
a) Count C-C bonds and C-H bonds separately, then add.
b) For an alkane {{CnH2n+2}} the total number of bonds is 3n + 1.

5. A hydrocarbon reacts with ammonical cuprous chloride solution to form a red precipitate .The hydrocarbon is
i) ethane
ii) ethene
iii) butane
iv) 1-propyne

Answer: iv) 1-propyne

1. Ammoniacal cuprous chloride gives a red precipitate only with terminal alkynes, which have a hydrogen on the triple-bonded carbon.
2. Of the options, only 1-propyne (CH₃-C≡CH) is a terminal alkyne.
3. Hence, the correct option is iv) 1-propyne.

Teacher's Note:
a) Ethane, ethene and butane have no terminal triple bond.
b) This test separates terminal alkynes from alkenes and alkanes.

6. Which of the following substance is added to denature Ethanol ?
i) methanol
ii) pyridine
iii) copper sulphate
iv) all of them

Answer: iv) all of them

1. Denatured alcohol is ethanol made unfit for drinking by adding poisonous or bad-smelling substances.
2. Methanol, pyridine and copper sulphate are all used for this purpose.
3. Hence, the correct option is iv) all of them.

Teacher's Note:
a) Denaturing prevents misuse of industrial ethanol as a drink.
b) Methanol is the common one, pyridine gives a foul smell, and copper sulphate gives a colour.

7. Which of the following is not an allotropic form of carbon
i) fluorine
ii) fullerene
iii) diamond
iv) graphite

Answer: i) fluorine

1. Fullerene, diamond and graphite are different forms of the element carbon.
2. Fluorine is a different element, a halogen.
3. Hence, the correct option is i) fluorine.

Teacher's Note:
a) Allotropes are forms of the same element.
b) Do not confuse "fluorine" with "fullerene".

8. Which of the following represents the correct decreasing order of hydrogen atoms ?
i) alkanes , alkenes , alkynes
ii) alkanes , alkaynes , alkenes
iii) alkenes , alkynes , alkanes
iv) alkynes , alkanes , alkenes

Answer: i) alkanes , alkenes , alkynes

1. For the same number of carbon atoms, the alkane has CnH₂n+2, the alkene CnH₂n and the alkyne CnH₂n-2.
2. So the number of hydrogen atoms decreases in the order alkanes, alkenes, alkynes.
3. Hence, the correct option is i).

Teacher's Note:
a) Compare ethane {{C2H6}}, ethene {{C2H4}} and ethyne {{C2H2}} for the same carbon number.
b) More bonds between carbons means fewer hydrogen atoms.

9. Detergents are sodium or potassium salts of long chain of ;-
i) aldehydes
ii) ketones
iii) carboxylic acid
iv) sulphonic acid

Answer: iv) sulphonic acid

1. Soaps are sodium or potassium salts of long-chain carboxylic acids.
2. Detergents are sodium or potassium salts of long-chain sulphonic acids.
3. Hence, the correct option is iv) sulphonic acid.

Teacher's Note:
a) Soap comes from carboxylic acids and detergent from sulphonic acids.
b) Option iii) describes soaps, so it is the trap.

10. Which of the following represents the structure of N₂ Mmolecule ?
i) N≡ N
ii) N = N
iii) N - N
iv) None of the above

Answer: i) N≡ N

1. Each nitrogen atom has 5 valence electrons and needs 3 more to complete its octet.
2. So two nitrogen atoms share three pairs of electrons and form a triple bond.
3. Hence, the correct option is i) N≡ N.

Teacher's Note:
a) Nitrogen needs three electrons, so its covalency is 3.
b) A triple bond is the reason nitrogen gas is so unreactive.

11. In double covalent bond there is sharing of
i) 2 electrons
ii) 4 electrons
iii) 6 electrons
iv) 3 electrons

Answer: ii) 4 electrons

1. A double bond has two shared pairs of electrons.
2. Number of electrons shared = 2 × 2 = 4.
3. Hence, the correct option is ii) 4 electrons.

Teacher's Note:
a) Single bond: 2 electrons, double bond: 4 electrons, triple bond: 6 electrons.
b) Count electrons, not pairs.

12. Cation is formed when
i) atom gains electrons
ii) atom loses electrons
iii) proton is lost by the atom
iv) atom shared by electrons

Answer: ii) atom loses electrons

1. A cation is a positively charged ion.
2. An atom becomes positive when it loses one or more electrons.
3. Hence, the correct option is ii) atom loses electrons.

Teacher's Note:
a) Losing electrons gives a cation and gaining electrons gives an anion.
b) Protons are never lost in a chemical reaction.

13. The total no. of electrons that take part in forming a bond in N₂ is
i) 2
ii) 4
iii) 6
iv) 10

Answer: iii) 6

1. N₂ has a triple bond, N≡N.
2. A triple bond means 3 shared pairs of electrons.
3. Number of electrons = 3 × 2 = 6.
4. Hence, the correct option is iii) 6.

Teacher's Note:
a) Multiply the number of bonds by 2 to get the shared electrons.
b) The 10 electrons in option iv) is the total number of valence electrons of both atoms.

14. Which of the following has the weakest carbon-carbon strength?
i) C₂H₂
ii) C₂H₄
iii) C₂H₆
iv) all have the same bond strength

Answer: iii) C₂H₆

1. C₂H₂ has a triple bond, C₂H₄ a double bond and C₂H₆ a single bond between the carbon atoms.
2. Bond strength increases with the number of bonds, so the single bond in C₂H₆ is the weakest.
3. Hence, the correct option is iii) C₂H₆.

Teacher's Note:
a) Triple bond is stronger than double bond, and double bond is stronger than single bond.
b) The bond length goes in the reverse order.

15. Which of the following salt when dissolved in water produce hard water.
i) calcium sulphate
ii) magnesium bicarbonate
iii) calcium chloride
iv) any of the above

Answer: iv) any of the above

1. Hard water contains dissolved calcium and magnesium salts.
2. Calcium sulphate, magnesium bicarbonate and calcium chloride are all such salts.
3. Hence, the correct option is iv) any of the above.

Teacher's Note:
a) Ca²⁺ and Mg²⁺ ions make water hard.
b) Bicarbonates cause temporary hardness; sulphates and chlorides cause permanent hardness.

16. Which of the following is not a saturated hydrocarbon ?
i) cyclohexane
ii) benzene
iii) butane
iv) isobutane

Answer: ii) benzene

1. Cyclohexane, butane and isobutane have only single bonds, so they are saturated.
2. Benzene has alternate double bonds in the ring, so it is unsaturated.
3. Hence, the correct option is ii) benzene.

Teacher's Note:
a) Saturated hydrocarbons have only C-C single bonds.
b) Benzene is a ring compound but not a saturated one.

17. The bond between two identical nonmetallic atom has a pair of electron ?
i) unequally shared between two atoms
ii) transferred completely from one atom to another
iii) With identical spins
iv) Equally shared between them

Answer: iv) Equally shared between them

1. Two identical non-metal atoms have the same electronegativity.
2. They share the pair of electrons equally and form a covalent bond.
3. Hence, the correct option is iv) Equally shared between them.

Teacher's Note:
a) Complete transfer of electrons gives an ionic bond, not a covalent bond.
b) Examples are {{H2}}, {{Cl2}} and {{O2}}.

18. Covalent compounds are generally -
i) Soluble in water
ii) insoluble in water
iii) Ionize in water
iv) hydrolyse in water

Answer: ii) insoluble in water

1. Covalent compounds consist of neutral molecules.
2. They are generally insoluble in water but dissolve in organic solvents.
3. Hence, the correct option is ii) insoluble in water.

Teacher's Note:
a) They do not ionise in water, so they do not conduct electricity.
b) Sugar and alcohol are covalent compounds that do dissolve, but these are exceptions.

19. Propane with molecular formula C₃H₈ has -
i) 7 covalent bonds
ii) 8 covalent bonds
iii) 9 covalent bonds
iv) 10 covalent bonds

Answer: iv) 10 covalent bonds

1. Propane has 2 C-C bonds and 8 C-H bonds.
2. Total = 2 + 8 = 10 covalent bonds.
3. Hence, the correct option is iv) 10 covalent bonds.

Teacher's Note:
a) Draw the structure of propane and count every bond.
b) Do not count only the C-H bonds.

20. A hydrocarbon reacts with ammonical cuprous chloride solution to form a red precipitate, the hydrocarbon is -
i) Ethane
ii) ethane
iii) butane
iv) 1-propyne

Answer: iv) 1-propyne

1. A red precipitate with ammoniacal cuprous chloride is given by terminal alkynes.
2. 1-propyne (CH₃-C≡CH) is the only terminal alkyne among the options.
3. Hence, the correct option is iv) 1-propyne.

Teacher's Note:
a) The first two options are printed as "Ethane" and "ethane"; the second one is meant to be ethene, which also gives no precipitate.
b) Alkanes and alkenes do not give this test.

21. Which of the following substance is added to denature Ethanol?
i) Methanol
ii) pyridine
iii) copper sulphate
iv) all of these

Answer: iv) all of these

1. Ethanol is denatured by adding small amounts of poisonous or foul-smelling substances.
2. Methanol, pyridine and copper sulphate are all used.
3. Hence, the correct option is iv) all of these.

Teacher's Note:
a) Denatured ethanol is unfit for drinking.
b) This cuts down the misuse of industrial alcohol.

22. Which of the following is not an allotropic form of carbon ?
i) fluorine
ii) fullerene
iii) diamond
iv) graphite

Answer: i) fluorine

1. Diamond, graphite and fullerene are crystalline allotropes of carbon.
2. Fluorine is a gaseous element of the halogen family.
3. Hence, the correct option is i) fluorine.

Teacher's Note:
a) Allotropes are different physical forms of one element.
b) Fullerene ({{C60}}) is the spelling to remember.

23. Which of the following represents the correct deceasing order of hydrogen atoms ?
i) alkanes, alkenes, alkynes
ii) alkanes, alkynes, alkenes
iii) alkenes, alkynes, alkanes
iv) alkynes, alkanes, alkenes

Answer: i) alkanes, alkenes, alkynes

1. Alkanes CnH₂n+2 have the most hydrogen atoms, then alkenes CnH₂n, then alkynes CnH₂n-2.
2. Hence, the correct option is i) alkanes, alkenes, alkynes.

Teacher's Note:
a) For the same carbon number, more bonds between carbons means fewer hydrogens.
b) The word "deceasing" in the question means decreasing.

24. Detergents are sodium or potassium salts of long chain of :
i) aldehydes
ii) ketones
iii) carboxylic acid
iv) sulphonic acid

Answer: iv) sulphonic acid

1. Soaps are salts of long-chain carboxylic acids.
2. Detergents are sodium or potassium salts of long-chain sulphonic acids.
3. Hence, the correct option is iv) sulphonic acid.

Teacher's Note:
a) Do not choose carboxylic acid, which is the source of soaps.
b) The sulphonate group lets detergents work in hard water.

25. In double covalent bond there is a sharing of
i) 2 electrons
ii) 4 electrons
iii) 6 electrons
iv) 3 electrons

Answer: ii) 4 electrons

1. A double bond has two shared pairs.
2. Shared electrons = 2 × 2 = 4.
3. Hence, the correct option is ii) 4 electrons.

Teacher's Note:
a) Single, double and triple bonds share 2, 4 and 6 electrons.
b) Count electrons and not bonds.

26. Cation is formed when
i) atom gains electrons
ii) atom losses electrons
iii) proton is lost by the atom
iv) atom shared by electrons

Answer: ii) atom losses electrons

1. An atom that loses electrons has more protons than electrons, so it carries a positive charge.
2. Such a positive ion is a cation.
3. Hence, the correct option is ii) atom losses electrons (that is, loses electrons).

Teacher's Note:
a) Metals form cations by losing their valence electrons.
b) Gain of electrons gives an anion.

27. The total number of electrons that take part in forming a bond in N₂ is
i) 2
ii) 4
iii) 6
iv) 10

Answer: iii) 6

1. Nitrogen atoms are joined by a triple bond, N≡N.
2. Three shared pairs mean 3 × 2 = 6 electrons.
3. Hence, the correct option is iii) 6.

Teacher's Note:
a) A triple bond means 6 shared electrons.
b) Each nitrogen atom contributes 3 electrons.

28. Which of the following has the weakest carbon-carbon strength ?
i) C₂H₂
ii) C₂H₄
iii) C₂H₆
iv) all have the same bond strength

Answer: iii) C₂H₆

1. C₂H₂ has a C≡C triple bond, C₂H₄ has a C=C double bond and C₂H₆ has a C-C single bond.
2. The single bond is the weakest of the three.
3. Hence, the correct option is iii) C₂H₆.

Teacher's Note:
a) More bonds between the same two atoms give a stronger and shorter link.
b) The single bond in ethane is the weakest.

29. Which of the following salt when dissolved in water produce hard water ?
i) calcium sulphate
ii) magnesium bicarbonate
iii) calcium chloride
iv) any of the above.

Answer: iv) any of the above.

1. Soluble salts of calcium and magnesium cause hardness of water.
2. All three salts listed are such salts.
3. Hence, the correct option is iv) any of the above.

Teacher's Note:
a) Hard water forms scum with soap.
b) Hardness is removed by boiling (temporary) or by adding washing soda (permanent).

30. The two colours seen at the extreme ends of the pH charts are:-
i) red and blue
ii) red and green
iii) green and blue
iv) orange and green

Answer: i) red and blue

1. On the universal indicator chart, strong acids (pH 0-1) are shown in red.
2. Strong bases (pH 13-14) are shown in dark blue or violet.
3. Hence, the correct option is i) red and blue.

Teacher's Note:
a) Red is the acid end and blue (or violet) is the basic end.
b) Green stands for neutral, pH 7.

31. Carboxylic acids on heating with P₂O₅ gives:-
i) ethers
ii) alcohol
iii) carbonyl compounds
iv) anhydrides

Answer: iv) anhydrides

1. P₂O₅ is a strong dehydrating agent and removes a molecule of water from two molecules of the acid.
2. 2CH₃COOH → (P₂O₅, heat) (CH₃CO)₂O + H₂O.
3. The product is an acid anhydride.
4. Hence, the correct option is iv) anhydrides.

Teacher's Note:
a) Two acid molecules lose one water molecule to form an anhydride.
b) {{P2O5}} acts as the dehydrating agent.

32. Synthetic flavours contain:-
i) unsaturated acids
ii) esters
iii) dilute carboxylic acids
iv) hydroxyl acids

Answer: ii) esters

1. Esters have a sweet, fruity smell.
2. They are used as artificial flavours in food and in perfumes.
3. Hence, the correct option is ii) esters.

Teacher's Note:
a) Esters give the fruity smell of ripe fruit.
b) Ethyl ethanoate is a common example.

33. Out of the following which one is used as preservative for pickle and sauces:-
i) esters
ii) acetone
iii) aldehyde
iv) acetic acid

Answer: iv) acetic acid

1. Acetic acid (vinegar) kills the micro-organisms that spoil food.
2. So it is used to preserve pickles and sauces.
3. Hence, the correct option is iv) acetic acid.

Teacher's Note:
a) Vinegar is a 5 to 8 percent solution of acetic acid in water.
b) Esters are used for flavour, not for preserving.

34. Brisk effervescences produced when a pinch of Na₂CO₃ is added to CH₃COOH is due to the formation of :-
i) H₂ gas
ii) CO₂ gas
iii) CO gas
iv) CH₄ gas

Answer: ii) CO₂ gas

1. Ethanoic acid reacts with sodium carbonate.
2. 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂.
3. The brisk bubbles are carbon dioxide gas.
4. Hence, the correct option is ii) CO₂ gas.

Teacher's Note:
a) Carbonates and bicarbonates release {{CO2}} with acids.
b) Hydrogen gas comes only from the reaction with metals such as sodium.

35. When an acetic acid reacts with an alcohol in the presence of conc. H₂SO₄:-
i) esters are formed
ii) ketones are formed
iii) aldehydes are formed
iv) none of these

Answer: i) esters are formed

1. Acetic acid and an alcohol react in the presence of conc. H₂SO₄ to form an ester and water.
2. CH₃COOH + C₂H₅OH → (conc. H₂SO₄) CH₃COOC₂H₅ + H₂O.
3. Hence, the correct option is i) esters are formed.

Teacher's Note:
a) This reaction is called esterification.
b) Conc. {{H2SO4}} acts as a catalyst and a dehydrating agent.

36. Sodium bi carbonate solution is added to dilute Ethanoic acid. It is observed that:-
i) a gas evolves
ii) a solid settles at the bottom
iii) the mixture becomes vapour
iv) the colour of the mixture becomes light Yellow

Answer: i) a gas evolves

1. CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂.
2. Carbon dioxide gas is released with brisk bubbling.
3. Hence, the correct option is i) a gas evolves.

Teacher's Note:
a) The gas is carbon dioxide and it turns lime water milky.
b) No solid settles and no colour change takes place.

37. Ethanoic acid was added to sodium bicarbonate sol. And the gas evolved was tested with a burning splinter. The following four observations were reported:-
1) the gas burns with the pop sound and the flame gets extinguished.
2) the gas does not burn out but the splinter burns with a pop sound
3) the flame extinguishes and the gas does not burn
4) the gas burns with a blue flame and the splinter burns brightly.
The correct observation is reported in:-
i) 1
ii) 2
iii) 3
iv) 4

Answer: iii) 3

1. The gas evolved is carbon dioxide.
2. Carbon dioxide does not burn and does not support burning, so the flame of the splinter goes out.
3. The pop sound is for hydrogen, which is not formed here.
4. Hence, the correct option is iii) 3.

Teacher's Note:
a) A pop sound with a burning splinter indicates hydrogen gas, not carbon dioxide.
b) Carbon dioxide extinguishes the flame.

38. 2ml of ethanoic acid was taken in each test tube 1 and 2 .A red litmus paper was introduced in test tube 1 and a pH paper was introduced in test tube 2. The experiment was performed by 4 students A, B, C, D and they reported their observation as given in the table.
The correct observation is reported in
i) A
ii) B
iii) C
iv) D

Answer: iv) D

1. Ethanoic acid is a weak acid.
2. An acid does not change the colour of red litmus, so it remains unchanged.
3. An acid turns pH paper pink or orange-red, because its pH is about 3.
4. Only student D reports both observations correctly.
5. Hence, the correct option is iv) D.

Teacher's Note:
a) Acids turn blue litmus red and have no effect on red litmus.
b) Green and blue colours of pH paper indicate neutral and basic solutions.

39. Acetic acid was added to a solid X kept in a Test tube. A colourless, odourless gas Y was evolved. The gas was passed through the lime water, which turned milky. It concludes that:-
i) solid X is NaOH and the gas Y is CO₂
ii) solid X is Na₂CO₃ and the gas Y is CO₂
iii) solid X is sodium acetate and the gas y is CO₂
iv) solid X is sodium chloride and the gas Y is CO₂

Answer: ii) solid X is Na₂CO₃ and the gas Y is CO₂

1. A gas that turns lime water milky is carbon dioxide.
2. Acetic acid releases CO₂ only from a carbonate or bicarbonate.
3. So X is sodium carbonate: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂.
4. Hence, the correct option is ii).

Teacher's Note:
a) NaOH only gives a salt and water with an acid, and no gas.
b) Sodium acetate and sodium chloride do not release carbon dioxide with acetic acid.

40. Why is carbon tetravalent?

Answer:
1. Carbon has atomic number 6 and its electronic configuration is 2, 4.
2. It has 4 electrons in its outermost shell.
3. It cannot easily lose or gain 4 electrons, so it shares them with other atoms.
4. Hence, carbon forms four covalent bonds and is tetravalent.

Teacher's Note:
a) Valency = number of electrons shared to complete the octet.
b) Carbon completes its octet by sharing 4 electrons.

41. The formula of a hydrocarbon is CnH₂n. Name the family to which it belongs and also predicts its nature.

Answer:
1. The general formula CnH₂n belongs to the alkene family.
2. Alkenes have a C=C double bond, so they are unsaturated hydrocarbons.
3. They are more reactive than alkanes and undergo addition reactions.
4. They burn with a yellow, sooty flame.

Teacher's Note:
a) Alkane {{CnH2n+2}}, alkene {{CnH2n}}, alkyne {{CnH2n-2}}.
b) Unsaturated means addition reactions are possible.
c) Quote the flame colour as a test.

42. What is the valency of carbon in CH₃-CH₃, CH₂=CH₂ and HC=CH ?

Answer:
1. In CH₃-CH₃ each carbon forms 3 C-H bonds and 1 C-C bond, so its valency is 4.
2. In CH₂=CH₂ each carbon forms 2 C-H bonds and a double bond (2 bonds), so its valency is 4.
3. In HC≡CH (printed as HC=CH) each carbon forms 1 C-H bond and a triple bond (3 bonds), so its valency is 4.
4. Hence, the valency of carbon is 4 in all three compounds.

Teacher's Note:
a) Carbon is always tetravalent.
b) Count each double bond as two valencies and each triple bond as three.

43. Out of butter and ground nut oil , which is unsaturated in Nature?

Answer:
1. Butter is an animal fat and contains saturated fatty acids.
2. Ground nut oil is a vegetable oil and contains unsaturated fatty acids with double bonds.
3. Hence, ground nut oil is unsaturated in nature.

Teacher's Note:
a) Animal fats are saturated and vegetable oils are unsaturated.
b) Unsaturated oils decolourise bromine water.

44. Why is high temperature not favourable for alcoholic fermentation?

Answer:
1. Fermentation is carried out by the enzyme zymase present in yeast.
2. Enzymes work best at about 25 to 35 °C.
3. At a high temperature the enzyme is destroyed (denatured), so fermentation stops.

Teacher's Note:
a) Enzymes are proteins and are damaged by heat.
b) Yeast stays active only in a warm range.

45. Name a cyclic unsaturated hydrocarbon, containing three double bonds?

Answer:
1. The cyclic hydrocarbon with three double bonds is benzene.
2. Its molecular formula is C₆H₆ and it has a six-membered ring with alternate double bonds.

Teacher's Note:
a) Benzene is the simplest aromatic compound.
b) The ring has three double bonds and three single bonds alternately.

46. What is the difference in the molecular mass of any two adjacent homologues?

Answer:
1. Adjacent homologues differ by one -CH₂- group.
2. Mass of CH₂ = 12 + 2 × 1 = 14 u.
3. Hence, the difference in molecular mass is 14 u.

Teacher's Note:
a) Homologues differ by a {{CH2}} unit.
b) The atomic masses used are C = 12 u and H = 1 u.

47. Which has triple bond ; C₂H₄ ,C₃H₆ and C₃H₄ ?

Answer:
1. The general formula of alkynes is CnH₂n-2.
2. For n = 3, C₃H₄ fits this formula, but C₂H₄ and C₃H₆ fit CnH₂n (alkenes).
3. Hence, C₃H₄ (propyne) has a triple bond.

Teacher's Note:
a) Compare each formula with {{CnH2n-2}}.
b) {{C2H4}} and {{C3H6}} have only a double bond.

48. Which substance is added to denature ethyl alcohol?

Answer:
1. Methanol is added to ethyl alcohol to denature it.
2. Pyridine or copper sulphate can also be used.
3. Denatured alcohol is poisonous and unfit for drinking.

Teacher's Note:
a) Name methanol as the main denaturant.
b) Denaturing stops people from drinking industrial alcohol.

49. Which ions are responsible for making water hard?

Answer:
1. The soluble salts of calcium and magnesium make water hard.
2. The ions responsible are calcium ions (Ca²⁺) and magnesium ions (Mg²⁺).

Teacher's Note:
a) Hard water gives scum with soap.
b) Both ions carry a charge of 2+.

50. Name the catalyst commonly used in hydrogenation of oil to form fats?

Answer:
1. Nickel (Ni) is the catalyst commonly used in the hydrogenation of oils.
2. Palladium can also be used.

Teacher's Note:
a) Hydrogenation: unsaturated oil + {{H2}} gives saturated fat.
b) Nickel is the cheap, common catalyst.

51. Write the name and molecular formula of alcohol derived from butane ?

Answer:
1. Replacing one hydrogen of butane (C₄H₁₀) with an -OH group gives butanol.
2. Name: butan-1-ol (butanol).
3. Molecular formula: C₄H₉OH or C₄H₁₀O.

Teacher's Note:
a) Alcohol: replace the -e of the alkane by -ol.
b) The formula changes from {{CnH2n+2}} to {{CnH2n+1OH}}.

52. Which gas is evolved when sodium carbonate or bicarbonate is added to ethanoic acid?

Answer:
1. Ethanoic acid reacts with sodium carbonate or bicarbonate to form sodium ethanoate, water and carbon dioxide.
2. Hence, carbon dioxide (CO₂) gas is evolved.

Teacher's Note:
a) The gas turns lime water milky.
b) Brisk effervescence is the sign of the reaction.

53. What is SCUM ?

Answer:
1. When soap is used in hard water, the calcium and magnesium salts present in the water react with it.
2. This forms an insoluble, sticky white precipitate of calcium or magnesium salts of fatty acids.
3. This precipitate is called scum.
4. It sticks to clothes and reduces the cleaning action of soap.

Teacher's Note:
a) Scum is formed only with soaps, not detergents.
b) It is a waste of soap in hard water.

54. What are hydrophobic and hydrophilic parts in soaps?

Answer:
1. A soap molecule has two parts: a long hydrocarbon chain and an ionic carboxylate end.
2. The long hydrocarbon chain is the hydrophobic (water-hating) part. It dissolves in oil and grease.
3. The ionic carboxylate end (-COO^-Na⁺) is the hydrophilic (water-loving) part. It dissolves in water.

Teacher's Note:
a) Hydro means water, phobic means fear and philic means love.
b) The tail enters the oil and the head stays in water in a micelle.

55. How much percentage of earth’s crust constitutes carbon element ?

Answer:
1. Carbon makes up only about 0.02% of the earth’s crust, in the form of minerals.
2. The atmosphere contains about 0.03% carbon dioxide.

Teacher's Note:
a) Carbon is a small part of the crust but forms millions of compounds.
b) Remember the figure 0.02%.

56. What do you mean by covalency ?

Answer:
1. Covalency is the number of electrons that an atom shares with other atoms to complete its octet.
2. It is equal to the number of covalent bonds the atom forms.
3. For example, the covalency of carbon is 4 and that of hydrogen is 1.

Teacher's Note:
a) Covalency is the number of shared electrons from one atom.
b) Do not mix it up with ionic charge.

57. What is covalent bond ?

Answer:
1. A covalent bond is a chemical bond formed by the mutual sharing of electrons between two atoms.
2. Both atoms attain the stable electronic configuration of a noble gas.
3. Example: in H₂ the two hydrogen atoms share one pair of electrons (H-H).

Teacher's Note:
a) Covalent bonds form between non-metals.
b) The shared pair belongs to both atoms.

58. What is functional group ?

Answer:
1. A functional group is an atom or a group of atoms present in an organic compound that decides its chemical properties.
2. Examples: -OH (alcohol), -CHO (aldehyde), >C=O (ketone) and -COOH (carboxylic acid).

Teacher's Note:
a) The functional group decides the properties, not the carbon chain.
b) Compounds with the same group show similar reactions.

59. What is organic chemistry ?

Answer:
1. Organic chemistry is the branch of chemistry that deals with the study of carbon compounds.
2. It covers hydrocarbons and their derivatives.
3. It excludes simple compounds such as oxides of carbon, carbonates and bicarbonates.

Teacher's Note:
a) Originally it was the study of compounds from living things.
b) Carbon forms a huge number of compounds because of catenation.

60. What name is given to the reaction which take place when Ethanoic acid reacts with ethanol in the presence of conc. Sulphuric acid ? Name the products obtained in this reaction.

Answer:
1. The reaction is called esterification.
2. CH₃COOH + C₂H₅OH → (conc. H₂SO₄) CH₃COOC₂H₅ + H₂O.
3. The products are ethyl ethanoate (an ester) and water.

Teacher's Note:
a) Acid + alcohol gives ester + water.
b) Conc. sulphuric acid is the catalyst and removes the water formed.

61. What is bromination ? Write the structural formula of product obtained on bromination of propene.

Answer:
1. Bromination is the reaction of a compound with bromine. Unsaturated hydrocarbons add bromine across the double bond.
2. CH₃-CH=CH₂ + Br₂ → CH₃-CHBr-CH₂Br.
3. The product is 1,2-dibromopropane. Its structural formula is CH₃-CHBr-CH₂Br.

Teacher's Note:
a) The red-brown colour of bromine disappears in this reaction.
b) This is the test for unsaturation.

62. Define covalency ?

Answer:
1. Covalency is the number of electrons that an atom contributes to share with other atoms to form covalent bonds.
2. It is equal to the number of covalent bonds formed by the atom.
3. The covalency of carbon is 4.

Teacher's Note:
a) Define it in terms of shared electrons.
b) Give an example to earn full credit.

63. Write the structural formula of the isomers of n-butane?

Answer:
1. n-Butane has the molecular formula C₄H₁₀.
2. Straight-chain isomer, n-butane: CH₃-CH₂-CH₂-CH₃.
3. Branched-chain isomer, isobutane (2-methylpropane): CH₃-CH(CH₃)-CH₃.

Teacher's Note:
a) Isomers have the same molecular formula but different structures.
b) {{C4H10}} has exactly two isomers.

64. Name the organic acid present in vinegar. Write its Chemical formula also.

Answer:
1. The organic acid present in vinegar is acetic acid (ethanoic acid).
2. Its chemical formula is CH₃COOH.

Teacher's Note:
a) Vinegar is a 5 to 8 percent solution of acetic acid.
b) Both names, acetic acid and ethanoic acid, are accepted.

65. The structural formula of an ester is HCOOCH₂CH₂CH₃ write the formula of acid and the alcohol from which it is made ?

Answer:
1. The ester HCOOCH₂CH₂CH₃ is propyl methanoate.
2. The part before -COO- gives the acid: HCOOH (methanoic acid).
3. The part after -COO- gives the alcohol: CH₃CH₂CH₂OH (propan-1-ol).
4. HCOOH + CH₃CH₂CH₂OH → HCOOCH₂CH₂CH₃ + H₂O.

Teacher's Note:
a) In an ester R-COO-R′, R-COO- comes from the acid and R′ from the alcohol.
b) Hydrolysis of the ester gives back both.

66. What happens when ethanol reacts with
(i) sodium
(ii) potassium permanganate solution.

Answer:
1. (i) Ethanol reacts with sodium to give sodium ethoxide and hydrogen gas, which burns with a pop sound: 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂.
2. (ii) Alkaline potassium permanganate oxidises ethanol to ethanoic acid, and the purple colour of the solution disappears: CH₃CH₂OH → (alkaline KMnO₄, heat) CH₃COOH.

Teacher's Note:
a) Sodium gives hydrogen gas and sodium ethoxide.
b) {{KMnO4}} acts as an oxidising agent.

67. Which of the following hydrocarbons undergo addition reactions : C₂H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄.

Answer:
1. Addition reactions are given only by unsaturated hydrocarbons.
2. C₂H₆, C₃H₈ and CH₄ fit CnH₂n+2, so they are saturated.
3. C₃H₆ (CnH₂n, alkene) and C₂H₂ (CnH₂n-2, alkyne) are unsaturated.
4. Hence, C₃H₆ and C₂H₂ undergo addition reactions.

Teacher's Note:
a) Check the general formula of each hydrocarbon.
b) Saturated compounds give substitution reactions instead.

68. What is hydrogenation ? Write its industrial application.

Answer:
1. Hydrogenation is the addition of hydrogen to an unsaturated hydrocarbon in the presence of a catalyst such as nickel or palladium to form a saturated hydrocarbon.
2. CH₂=CH₂ + H₂ → (Ni) CH₃-CH₃.
3. Industrial application: vegetable oils (unsaturated) are converted into vegetable ghee (saturated fat) by hydrogenation.

Teacher's Note:
a) Nickel catalyst and heat are needed.
b) Hydrogenation turns liquid oils into solid fats.

69. Give a test that can be used to differentiate between butter and cooking oil ?

Answer:
1. Take a little of each sample and add a few drops of bromine water to each, then shake.
2. The cooking oil is unsaturated, so it decolourises the bromine water.
3. Butter is saturated, so the colour of bromine water remains.

Teacher's Note:
a) Bromine water is the test for unsaturation.
b) Decolourisation means the sample is unsaturated.

70. Give the names of the functional group:-
(i) -CHO
(ii) -C=O
( iii) -OH
(iv) -COOH

Answer:
1. (i) -CHO is the aldehyde group.
2. (ii) -C=O (>C=O) is the ketone group.
3. (iii) -OH is the alcohol (hydroxyl) group.
4. (iv) -COOH is the carboxylic acid group.

Teacher's Note:
a) Learn each group with one example.
b) The ketone group is inside the carbon chain, but the aldehyde group is at the end.

71. Explain the following terms :
a) Etherification
b) Saponification
c) Dehydration

Answer:
1. a) Etherification: formation of an ether by removing a molecule of water from two molecules of an alcohol with conc. H₂SO₄ at about 413 K. 2C₂H₅OH → C₂H₅-O-C₂H₅ + H₂O.
2. b) Saponification: alkaline hydrolysis of an ester (a fat or oil) with sodium hydroxide to form soap and glycerol.
3. c) Dehydration: removal of water from a compound. For example, ethanol heated with conc. H₂SO₄ at 443 K gives ethene: C₂H₅OH → CH₂=CH₂ + H₂O.

Teacher's Note:
a) Saponification is the reaction that makes soap.
b) Temperature decides the product in the action of conc. {{H2SO4}} on ethanol: 443 K gives ethene and 413 K gives ether.
c) Write one equation for each term.

72. An organic compound A having molecular fomula C₂H₄O₂ reacts with Sodium metal Na evolves a gas B which readily catches fire. A also reacts with Ethanol in the presence of concentrated Sulphuric acid to form a sweet smelling substance C in making perfumes.
a) Identify the compounds A, B and C.
b) Write balanced chemical equation to represent the conversion of
(i). Compound A to compound B.
(ii). Compound A to compound C.

Answer:
1. a) A is ethanoic acid (CH₃COOH), because it reacts with sodium and with ethanol to form an ester.
2. B is hydrogen gas (H₂), which readily catches fire.
3. C is ethyl ethanoate (CH₃COOC₂H₅), the sweet-smelling ester.
4. b) (i) 2CH₃COOH + 2Na → 2CH₃COONa + H₂
5. b) (ii) CH₃COOH + C₂H₅OH → (conc. H₂SO₄) CH₃COOC₂H₅ + H₂O

Teacher's Note:
a) Acid with sodium gives hydrogen; acid with alcohol gives an ester.
b) Balance each equation before writing the final answer.

73. Give the name of the following :
a) An Aldehyde derived from Ethane.
b) Ketone derived from Butane.
c) The compound obtained by the Oxidation of Ethanol by Chromic anhydride.

Answer:
1. a) The aldehyde derived from ethane is ethanal (CH₃CHO).
2. b) The ketone derived from butane is butanone (CH₃COCH₂CH₃).
3. c) Oxidation of ethanol with chromic anhydride gives ethanoic acid (CH₃COOH).

Teacher's Note:
a) Aldehyde names end in -al and ketone names end in -one.
b) Strong oxidising agents convert ethanol into the acid.

74. Write chemical equations of the reactions of Ethanoic acid with :
a) Sodium
b) Sodium Carbonate
c) Ethanol in the presence of conc. H₂SO₄.

Answer:
1. a) 2CH₃COOH + 2Na → 2CH₃COONa + H₂
2. b) 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂
3. c) CH₃COOH + C₂H₅OH → (conc. H₂SO₄) CH₃COOC₂H₅ + H₂O

Teacher's Note:
a) Balance every equation.
b) Ethanoic acid gives hydrogen with metals, {{CO2}} with carbonates and an ester with alcohols.

75. Give a test to distinguish between:
a) Ethane and Ethene
b) Ethanol with Ethanoic acid.
c) Soaps and detergents.

Answer:
1. a) Add bromine water to both. Ethene decolourises it (unsaturated); ethane does not.
2. b) Add sodium bicarbonate to both. Ethanoic acid gives brisk effervescence of CO₂; ethanol does not. (Blue litmus also turns red with ethanoic acid only.)
3. c) Shake each with hard water. Soap forms a curdy white scum and little lather; a detergent forms lather without scum.

Teacher's Note:
a) Each test must give a clear visible change.
b) State the result for both compounds.

76. Complete the following reactions:
a) H₂C=CH₂ + H₂O H₂SO₄
b) HC≡CH + Br₂
c) C₂H₅OH + Na
d) CH₃COOH + C₂H₅OH

Answer:
1. a) CH₂=CH₂ + H₂O → (H₂SO₄) CH₃CH₂OH (ethanol)
2. b) HC≡CH + Br₂ → CHBr=CHBr (1,2-dibromoethene)
3. c) 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
4. d) CH₃COOH + C₂H₅OH → (conc. H₂SO₄) CH₃COOC₂H₅ + H₂O

Teacher's Note:
a) In (b) with excess bromine the product is {{CHBr2-CHBr2}}.
b) Name the type of reaction: (a) addition, (b) addition, (c) substitution of hydrogen by sodium, (d) esterification.

77. Two carbon compounds A and B have the molecular formula C₃H₈ and C₃H₆ respectively. Which one of the two each most likely to show addition reaction? Justify your answer. Explain with the help of a chemical equation, how an addition is useful in vegetable Ghee industry.

Answer:
1. A (C₃H₈, propane) fits CnH₂n+2, so it is saturated. B (C₃H₆, propene) fits CnH₂n, so it has a double bond and is unsaturated.
2. Only unsaturated compounds add other molecules, so B (C₃H₆) is most likely to show an addition reaction.
3. In the ghee industry, vegetable oils (unsaturated) are hydrogenated in the presence of nickel to form saturated vegetable ghee.
4. CH₃-CH=CH₂ + H₂ → (Ni, 473 K) CH₃-CH₂-CH₃; in the same way an unsaturated oil is converted into a saturated fat.

Teacher's Note:
a) Unsaturated compounds undergo addition, saturated ones undergo substitution.
b) The same hydrogenation reaction turns liquid oil into solid ghee.
c) Write the catalyst over the arrow.

78. What substance should be oxidised to prepare acetic acid (CH₃COOH)? How can ethanol and Ethanoic acid be differentiated?

Answer:
1. Ethanol (C₂H₅OH) should be oxidised to prepare acetic acid, using alkaline KMnO₄ or acidified K₂Cr₂O₇.
2. CH₃CH₂OH + 2[O] → CH₃COOH + H₂O.
3. To differentiate: add sodium bicarbonate to both samples.
4. Ethanoic acid gives brisk effervescence of CO₂, while ethanol gives no gas.

Teacher's Note:
a) Oxidising agent: alkaline {{KMnO4}} or acidified {{K2Cr2O7}}.
b) Litmus can also be used, as only the acid turns blue litmus red.

79. Write down the difference between soap and detergent.

Answer:

Teacher's Note:
a) Compare composition, hard water action, source and biodegradability.
b) A table with four clear rows earns full credit.

80. An organic compound A is widely used as a preservative in pickles and has a molecular formula C₂H₄O₂. This compound reacts with ethanol to form a sweet smelling compound B.
i) Identify the compound A.
ii) Write the chemical equation for its reaction with Ethanol to form compound B.
iii) How can we get compound A back from B?
iv) Name the process and write corresponding chemical equation.
v) Which gas is produced when compound A reacts with washing soda? Write the chemical equation

Answer:
1. i) A is ethanoic acid (CH₃COOH).
2. ii) CH₃COOH + C₂H₅OH → (conc. H₂SO₄) CH₃COOC₂H₅ + H₂O; B is ethyl ethanoate.
3. iii) A is obtained back by the alkaline hydrolysis of ester B with sodium hydroxide, followed by acidification of the sodium ethanoate formed.
4. iv) The process is saponification. CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH
5. v) Carbon dioxide gas is produced. 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂

Teacher's Note:
a) Compound A is the acid used in pickles, that is, vinegar.
b) Hydrolysis of an ester gives back an alcohol and a carboxylate.
c) Balance the equation in part v) before writing it.

81. An organic compound X with a molecular formula C₂H₆O undergoes oxidation with in presence of alkaline KMnO₄ to a compound Y. X on heating in presence of Conc. H₂SO₄ at 443K gives Z.which on reaction with H₂O in presence of H₂SO₄ gives back `X`. `Z` reacts with Br₂ (aq) and decolorizes it. Identify X, Y, & Z.and write the reactions involved.

Answer:
1. X is ethanol (CH₃CH₂OH), Y is ethanoic acid (CH₃COOH) and Z is ethene (CH₂=CH₂).
2. Oxidation: CH₃CH₂OH → (alkaline KMnO₄, heat) CH₃COOH
3. Dehydration: CH₃CH₂OH → (conc. H₂SO₄, 443 K) CH₂=CH₂ + H₂O
4. Hydration: CH₂=CH₂ + H₂O → (H₂SO₄) CH₃CH₂OH
5. Bromine test: CH₂=CH₂ + Br₂ → CH₂Br-CH₂Br, so the colour of bromine water disappears.

Teacher's Note:
a) Z decolourises bromine water, so it is unsaturated, which is ethene.
b) Conc. {{H2SO4}} at 443 K dehydrates ethanol to ethene.
c) Write the conditions over each arrow.

82. An organic compound ‘A’ is widely used as a preservative in pickles and has a molecular formula C₂H₂O₂. This compound reacts with ethanol to form a sweet smelling compound ‘B’.
(i) Identify the compound ‘A’
(ii) Write the chemical equation for its reaction with ethanol to form compound ‘B’. (iii) How can we get compound ‘A’ back from ‘B’?
(iv) Name the process and write corresponding chemical equation.
(v) Which gas is produced when compound ‘A’ reacts with washing soda? Write the chemical equation.

Answer:
1. i) A is ethanoic acid (CH₃COOH). The formula printed as C₂H₂O₂ is a misprint of C₂H₄O₂.
2. ii) CH₃COOH + C₂H₅OH → (conc. H₂SO₄) CH₃COOC₂H₅ + H₂O; B is ethyl ethanoate.
3. iii) A is obtained back by hydrolysis of the ester with sodium hydroxide, followed by acidification.
4. iv) The process is saponification. CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH
5. v) Carbon dioxide gas is produced. 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂

Teacher's Note:
a) The formula of ethanoic acid is {{C2H4O2}}, not {{C2H2O2}}.
b) The sweet smell tells us that B is an ester.

83. Hydrocarbon `X` and `Y` having molecular formulae C₃H₈ and C₃H₆ respectively. Both are burnt in different spatula on the bunsen flame. Indicate the color of the flame produced by `X` and `Y`. Identify `X` and `Y`. Write the structural formulae.

Answer:
1. X (C₃H₈) fits CnH₂n+2, so it is propane, a saturated hydrocarbon. Structural formula: CH₃-CH₂-CH₃.
2. Y (C₃H₆) fits CnH₂n, so it is propene, an unsaturated hydrocarbon. Structural formula: CH₃-CH=CH₂.
3. X burns with a clean blue flame.
4. Y burns with a yellow, sooty flame.

Teacher's Note:
a) Saturated hydrocarbons burn with a blue flame and unsaturated ones with a sooty flame.
b) More carbon content gives a sooty flame because of incomplete combustion.

84. A compound `X` has molecular formula C₄H₁₀. It undergoes substitution reaction readily than addition reaction. It burns with blue flame and is present in LPG. Identify `X` and give the balanced equation for its combustion and substitution reaction with Cl₂ in presence of sunlight.

Answer:
1. X is butane (C₄H₁₀), a saturated hydrocarbon that is present in LPG.
2. Combustion: 2C₄H₁₀ + 13O₂ → 8CO₂ + 10H₂O + heat and light
3. Substitution: C₄H₁₀ + Cl₂ → (sunlight) C₄H₉Cl + HCl

Teacher's Note:
a) Check the atoms on both sides of the combustion equation: 8 C, 20 H and 26 O.
b) Saturated compounds give substitution reactions in sunlight.

85. `A` compound works well with hard water. It is used for making shampoos & products for cleaning clothes. A is not 100% biodegradable and causes water pollution. `B` does not work well with hard water. It is 100% biodegradable and does not create water pollution. Identify A & B.

Answer:
1. A works well with hard water and is not fully biodegradable, so A is a detergent.
2. B does not work well with hard water and is fully biodegradable, so B is soap.

Teacher's Note:
a) Soap: forms scum in hard water, biodegradable.
b) Detergent: works in hard water, many are not biodegradable.

86. An organic compound P with molecular formula C₂H₆O is an active ingredient of all alcoholic drinks. It is also used in medicines such as tincture iodine, cough syrups. Identify `P`. Drop a small piece of sodium into the test tube containing `P`.A new compound `Q` is formed with the evaluation of colorless and odorless gas Name the gas evolved and compound `Q` write the chemical reaction.

Answer:
1. P is ethanol (C₂H₅OH), the active ingredient of alcoholic drinks.
2. Sodium reacts with ethanol and releases hydrogen gas (H₂), which is colourless and odourless.
3. Q is sodium ethoxide (C₂H₅ONa).
4. 2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂

Teacher's Note:
a) The gas burns with a pop sound.
b) The same gas is formed when sodium reacts with ethanoic acid.

87. A cyclic compound `X` has molecular formula C₆H₆. It is unsaturated and burns with sooty flame. Identify `X` and write its structural formula. Will it decolorize bromine water or not and why?

Answer:
1. X is benzene (C₆H₆), a cyclic hydrocarbon with alternate double and single bonds in a six-carbon ring, as shown in the figure.
2. Although benzene is unsaturated, it will not decolourise bromine water.
3. The electrons of the three double bonds are spread over the whole ring (delocalised), which makes benzene very stable.
4. So it does not easily undergo addition reactions with bromine and gives substitution reactions instead.

Teacher's Note:
a) Benzene is an aromatic compound and burns with a sooty flame.
b) Unsaturation alone does not always mean that bromine water is decolourised.

88. An organic compounds `A` is a constituent of antifreeze and has the molecular formula C₂H₆O. upon reaction with alkaline KMnO₄, the compound `A` is oxidized to another `B` with formula C₂H₂O₂. Identify the compound A` and `B`. Write the chemical equation for the reaction which leads to the formulation of `B`

Answer:
1. A has the molecular formula C₂H₆O and is oxidised by alkaline KMnO₄, so A is ethanol (CH₃CH₂OH).
2. The product B is ethanoic acid (CH₃COOH). The formula printed as C₂H₂O₂ is a misprint of C₂H₄O₂.
3. CH₃CH₂OH + 2[O] → (alkaline KMnO₄, heat) CH₃COOH + H₂O

Teacher's Note:
a) Ethanol of formula {{C2H6O}} is the compound that is oxidised.
b) The formula of ethanoic acid is {{C2H4O2}}.

89. Two compounds `X` and `Y` have the same formula C₂H₄O₂. One of them reacts with sodium metal to liberate H₂ and CO₂ with NaHCO₃. Second one does not reacts with Na metal and NaHCO₃ but undergo hydrolysis with NaOH to form salt of carboxylic acid and compound `Z` which is called wood spirit. Identify `X`, `Y`, and `Z` and write chemical equation for the reaction involved.

Answer:
1. X reacts with sodium to give H₂ and with NaHCO₃ to give CO₂, so X is ethanoic acid (CH₃COOH).
2. Y does not react with Na or NaHCO₃ and is hydrolysed by NaOH, so Y is an ester, methyl methanoate (HCOOCH₃).
3. Z is wood spirit, which is methanol (CH₃OH).
4. Reaction of X: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂
5. Reaction of Y: HCOOCH₃ + NaOH → HCOONa + CH₃OH

Teacher's Note:
a) Acid and ester are isomers with the same formula {{C2H4O2}}.
b) Wood spirit is methanol.

90. A compound `X` with molecular formula C₂H₄ burns with a sooty flame. It decolourise bromine water. Identify `X`. Will it dissolve in water or not? Will it conduct electricity in aq. Solution? Will it have high melting point or low melting point ?

Answer:
1. X is ethene (CH₂=CH₂), an unsaturated hydrocarbon, since it burns with a sooty flame and decolourises bromine water.
2. It will not dissolve in water, because it is a non-polar covalent compound.
3. It will not conduct electricity in aqueous solution, because it does not form ions.
4. It has a low melting point, because the forces between its molecules are weak.

Teacher's Note:
a) Covalent compounds have weak forces between molecules, so low melting points.
b) Mention that ethene is insoluble in water but soluble in organic solvents.

Question. Which of the following statements is correct?
(a) Most organic compounds are ionic compounds.
(b) Ethane and ethene belong to the same homologous series.
(c) Propene contains three hydrogen atoms per molecule.
(d) Chloroethane contains two carbon atoms per molecule.
Answer. D

Question. All the members of homologous series of alkynes have the general formula
(a) C_nH_2n
(b) C_nH_{2n + 2}
(c) C_nH_{2n – 2}
(d) C_nH_{2n – 4}
Answer. C

Question. Three hydrocarbons X, Y and Z are shown below :
X : CH₃CH₂CH₂CH₂CH₃
Y : CH₃ —C ≡C —CH₂CH₃
Z : CH₃CH₂— CH ≡CH —CH₃
Identify the incorrect statements about these three hydrocarbons.
I. X and Y both differ by a CH₂ unit.
II. X and Z have the same boiling point.
III. All have different general formulae.
IV. Y and Z have different molecular masses.
(a) I and II
(b) II and III
(c) I and IV
(d) All the statements are incorrect
Answer. A

Question. Which of the following statements is correct about a substance that has a giant covalent structure?
(a) All its ions are arranged in a giant three dimensional lattice.
(b) A large amount of energy is needed to break down the lattice structure.
(c) It conducts electricity in the molten state.
(d) It dissolves in water but is more soluble in organic solvents.
Answer. B

Question. The general formula of cycloalkanes is
(a) C_nH_{2n + 2}
(b) C_nH_{2n – 2}
(c) C_nH_{2n – 1}
(d) C_nH_2n
Answer. D

Question. Which of the following exists as a simple triatomic molecule?
(a) Argon
(b) Fluorine
(c) Nitrogen
(d) Ozone
Answer. D

Question. Which of the following molecules has all its atoms joined together by double covalent bonds?
(a) Methane
(b) Water
(c) Carbon dioxide
(d) Nitrogen trichloride
Answer. C

Question. Which of the following is not a characteristic of members of a homologous series?
(a) They possess varying chemical properties.
(b) Their physical properties vary in regular and predictable manner.
(c) Their formulae fit the general molecular formula.
(d) Adjacent members differ by one carbon and two hydrogen atoms.
Answer. A

Question. Which covalent molecule contains the structure where the central atom is bonded to four other atoms by covalent bonds?
1. Diamond   2. Graphite
3. Methane   4. Silicon dioxide
(a) 1 and 2
(b) 2 and 4
(c) 3 and 4
(d) 1, 3 and 4
Answer. D

Question. Which of the following represent saturated hydrocarbons?
1. CH(CH₃)₃
2. CH₂CHCH₃
3. CH₃CH(CH₃)CH₂CH₃
4. (CH₃)₂CCHCH₃
(a) 1 and 3
(b) 2 and 4
(c) 1, 2 and 3
(d) 1, 2, 3 and 4
Answer. A

Question. Which type of bond is present between carbon-carbon atoms in acetylene?
(a) Single covalent bond
(b) Double covalent bond
(c) Triple covalent bond
(d) Electrovalent bond
Answer. C

Question. Number of free electron(s) in each carbon atom in graphite is/are
(a) two
(b) four
(c) one
(d) three.
Answer. C

Question. Which of the following statements is not correct?
(a) A common functional group is present in different members of a homologous series.
(b) Two consecutive members of a homologous series differ by a –CH3 group.
(c) The members of a homologous series can be represented by one general formula.
(d) Different members of a homologous series have similar chemical properties.
Answer. B

Question. Identify the correct statements.
(i) As the molecular mass increases in any homologous series, a gradation in physical properties is seen.
(ii) The melting and boiling points decrease with increasing molecular mass.
(iii) Other physical properties such as solubility in a particular solvent decreases with increasing molecular mass.
(iv) The chemical properties, which are determined solely by the functional group, remain similar in a homologous series.
(a) (ii) and (iii)
(b) (ii) and (iv)
(c) (i), (iii) and (iv)
(d) All are correct
Answer. C

CBSE Class 10 Science Chapter 4 Carbon and its compound Assertion and Reason

For question numbers 56-70, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(a) Both assertion and reason are true, and reason is correct explanation of the assertion.
(b) Both assertion and reason are true, but reason is not the correct explanation of the assertion.
(c) Assertion is true, but reason is false.
(d) Assertion is false, but reason is true.

Question. Assertion : In alkanes, alkenes and alkynes the valency of carbon is always four.
Reason : All hydrocarbons except alkanes contain double bonds.
Answer. C

Question. Assertion : Carbon possesses property of catenation.
Reason : Carbon atoms form double as well as triple bonds during catenation.
Answer. B

Question. Assertion : Ethanol is first member of the alcohol homologous series.
Reason : A homologous series can be represented by a general formula.
Answer. D

Question. Assertion : Diamond is the hardest natural known substance.
Reason : Diamond is used for cutting marble, granite and glass.
Answer. B

Question. Assertion : Diamond is not a good conductor of electricity.
Reason : It has no free electrons.
Answer. A

Question. Assertion : Two members of a homologous series have similar chemical properties.
Reason : Propane and butane are members of same homologous series.
Answer. B

Question. Assertion : Saturated hydrocarbons are chemically less reactive.
Reason : All the valencies of carbon atom are satisfied by single covalent bonds.
Answer. A

Question. Assertion : Covalent compounds are generally poor conductor of electricity.
Reason : They consist of molecules and not ions which can transfer charge.
Answer. A

Question. Assertion : Graphite is a good conductor of electricity.
Reason : It has one free valence electron.
Answer. A

Question. Assertion : The functional group present in alcohols is –OH.
Reason : It is the same group as present in water, hence water and alcohol have similar properties.
Answer. C

Question. Assertion : Diamond and graphite do not have the same crystal structure.
Reason : Diamond is crystalline while graphite is amorphous.
Answer. C

Question. Assertion : Carbon and its compounds can be used as fuels.
Reason : They are highly inflammable and have high calorific value.
Answer. A

Question. Assertion : Olefins have the general formula C_nH_2n+1.
Reason : There is atleast one double bond between two carbon atoms in their molecules.
Answer. D

Question. Assertion : Graphite is soft and slippery to touch.
Reason : Graphite has sheet like layered structure.
Answer. A

Question. Assertion : Both aldehydes and ketones contain carbonyl group.
Reason : In aldehydes, the functional group is attached to atleast one hydrogen atom.
Answer. B

CBSE Class 10 Science Chapter 4 Carbon and its compound Case Based MCQs

Case I : Read the passage given below and answer the following questions.

An organic molecule has the following structure :

Question. To which homologous series does this molecule belong?
(a) Aldehydes
(b) Ketones
(c) Alcohols
(d) Alkanes
Answer. C

Question. What is the general formula of this homologous series?
(a) C_nH_2n + 1OH
(b) C_nH_2n + 2
(c) C_nH_2nO
(d) C_nH_2n + 1CHO
Answer. A

Question.  Which is the next member of this series?
(a) C₄H₉OH
(b) C₃H₇OH
(c) C₅H₁₁OH
(d) C₆H₁₃OH
Answer. C

Question. Which is the second member of this series?
(a) Ethanol
(b) Methanol
(c) Propanol
(d) Butanol
Answer. A

Case II : Read the passage given below and answer the following questions.

When an element exists in two or more different forms in the same physical state, these different forms are called allotropes and the phenomenon is known as allotropy. Allotropes have similar chemical properties but they differ in their physical properties. Carbon exists in crystalline and amorphous forms. In crystalline form, it occurs as diamond, graphite and fullerenes. Diamond is a colourless, transparent substance having extraordinary brilliance. It is the hardest natural substance known. It is used for cutting marble, granite and glass. Graphite is a greyishblack, opaque substance. It is lighter than diamond i.e., it has lower density. It has sheet like structure having hexagonal layers. One layer slides over the other layer which makes it soft to touch. It is the reason that graphite is used as a lubricant.

Question. Substance X is a moderate conductor of electricity. Substance X has the structure shown below :
Which statements about substance X are correct?
(I) It is a covalent compound.
(II) It has a giant molecular structure.
(III)It has the same structure as graphite.
(IV) It has the same structure as diamond.
(a) (I) and (III)
(b) (II) and (III)
(c) (II) and (IV)
(d) (I), (II) and (IV)
Answer. C

Question. Which of the following is correct about the structure of diamond?
(a) Carbon atoms are held together by single covalent bonds.
(b) Electrons move freely through the structure.
(c) Layers of atoms slide easily over each other.
(d) Carbon atoms conduct electricity in the molten state.
Answer. A

Question. Which three allotropes of carbon, do the given figures represent?

Answer. D

Question. Identify the incorrect statement(s).
(I) Diamond is the hardest substance known while graphite is smooth and slippery.
(II) Diamond is made up of billions of carbon atoms. Each carbon atom is bonded to four other carbon atoms in a tetrahedral manner to form a giant lattice. All carbon atoms are bonded by strong covalent bonds.
(III) Graphite is a poor conductor of electricity unlike other non-metals.
(IV) Graphite has a giant covalent structure that is made up of layers of carbon atoms.
In each layer, each carbon atom is bonded to three other carbon atoms to form hexagonal rings of carbon atoms.
(a) (I) and (III)
(b) Only (III)
(c) (II) and (IV)
(d) (I), (II) and (IV)
Answer. B

Question. Structures of two different forms of carbon are given below :

Identify the two forms (I and II respectively) and how are they related to each other?
(a) Diamond, Graphite, Isotopes of carbon
(b) Graphite, Diamond, Allotropes of carbon
(c) C¹², C¹⁴, Allotropes of carbon
(d) C¹⁴, C¹², Isotopes of carbon
Answer. B