IGCSE Chemistry Paper-1: Specimen Questions with Answers 5 - 6 of 99

Question number: 5

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Question

A mixture containing two anions was tested and the results are shown below.

If dilute nitric acid added then effervescence of a gas which turned limewater milky

If dilute nitric acid added, followed by aqueous silver nitrate then yellow precipitate is formed

Which anions were present?

Choices

Choice (4)Response

a.

sulphate and iodide

b.

sulphate and chloride

c.

carbonate and chloride

d.

carbonate and iodide

Answer

d.

Explanation

For the test of carbonate ions:

  • Limewater (aqueous calcium hydroxide) is used to identify carbonate ions in solution.
  • Firstly a dilute acid is added to the solution. If carbonate ions are present carbon dioxide (CO2) gas will be given off.
  • If carbon dioxide is passed through limewater a cloudy white precipitate of calcium carbonate will be formed.

For the test of iodide ions:

Add dilute nitric acid and silver nitrate solution. The silver nitrate is acidified with dilute nitric acid to prevent the precipitation of other non–halide silver salts. Yellow precipitate of silver iodide will be formed.

Ag+ (aq) + I (aq) == > AgI (s) (Yellow Precipitate)

Question number: 6

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  1. The table shows the results of adding three metals, P, Q and R, to dilute hydrochloric acid and to water.

results of adding three metals, P, Q and R, to dilute hydrochloric acid

Finding the result if HCl is added to 3 different metals

Metal

Dilute hydrochloric acid

Water

P

Hydrogen produced

Hydrogen produced

Q

no reaction

No reaction

R

Hydrogen produced

No reaction

What is the order of reactivity of the metals?

Choices

Choice (4)Response

a.

most reactive is P next is Q and least reactive is R

b.

most reactive is R next is Q and least reactive is P

c.

most reactive is P next is R and least reactive is Q

d.

most reactive is R next is P and least reactive is Q

Answer

c.

Explanation

most metals are usually electropositive in nature and lose electrons in a chemical reaction they do not react with the same vigour or speed. Metals display different reactions towards different substances. The greater the ease with which an element loses its electrons and acquires a positive charge, the greater is its reactivity. In the above reactions we can see P reacted with diluted HCL and water rigorously to produce hydrogen.

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