IGCSE Chemistry Paper-1: Specimen Questions with Answers 83 - 84 of 99

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Question 83

Question

MCQ▾

Which of the following structure represents alcohol?

Choices

Choice (4)

a.

Correct Structure for Alcohol – Choice A

b.

Correct Structure for Alcohol – Choice B

c.

Question does not provide sufficient data or is vague

d.

None of the above

Answer

b.

Explanation

Alcohols are organic compounds consisting of hydroxyl group – OH attached to a carbon atom.

Choice B shows the structure of ethanol. Ethanol is the type of alcohol found in alcoholic drinks such as wine and beer. It is also useful as a fuel. For use in cars and other vehicles, it is usually mixed with petrol.

Question 84

Question

MCQ▾

Why carbon is found in so many chemical compounds?

Choices

Choice (4)

a.

Carbon is versatile because it can form single, double, and triple bonds. It can also form chains, branched chains, and rings when connected to other carbon atoms.

b.

Because of its tetra covalent nature.

c.

Both a. and b. are correct

d.

None of the above

Answer

c.

Explanation

Catenation occurs most readily in carbon, which forms covalent bonds with other carbon atoms to form longer chains and structures. This is the reason for the presence of the vast number of organic compounds in nature.

A carbon atom has a total of six electrons occupying the first two shells, i.e.. , the K-shell has two electrons and the L-shell has four electrons. This distribution indicates that in the outermost shell there are one completely filled “s” orbital and two half-filled ‘p’ orbitals, showing carbon to be a divalent atom. But in actuality, carbon displays tetravalency in the combined state. Therefore, a carbon atom has four valence electrons. It could gain four electrons to form C4- anion or lose four electrons to form C4 + cation. Both these conditions would take carbon far away from achieving stability by the octect rule. To overcome this problem carbon undergoes bonding by sharing its valence electrons. This allows it to be covalently bonded to one, two, three or four carbon atoms or atoms of other elements or groups of atoms.

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