IGCSE Chemistry: Specimen Questions with Answers 204 - 206 of 240

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Question 204

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Short Answer▾

The alkanes are a homologous series of hydrocarbons. What is meant by the term homologous series? (2 marks)

Explanation

In organic chemistry, a homologous series is a series of compounds with the same general formula, usually varying by a single parameter. This can be the length of a carbon chain, for example in the straight-chained alkanes (paraffins) , or it could be the number of monomers in a homopolymer such as amylose. As shown in the diagram.

Methane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
Pentane

Question 205

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Short Answer▾

Suggest why a solution of malonic acid, concentration 0.2 mol/dm3, has a higher pH than one of sulfuric acid of the same concentration.

[1 Marks]

Explanation

Because the sulfuric acid have low melting point and malonic has high melting point than malonic acid.

Question 206

Question

MCQ▾

Which of the statements about ethanol are correct?

1 Ethanol can be formed by an addition reaction.

2 Ethanol can be formed by fermentation.

3 When ethanol burns in air, it forms carbon dioxide and water.

Choices

Choice (4)

a.

b.

c.

d.

Answer

a.

Explanation

Correct option is A means all because Ethanol can be made by reacting ethene (from cracking crude oil fractions) with steam. The combustion of ethanol is an exothermic reaction so it forms , and heat. Ethanol can also be formed by fermentation of glucose

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