IGCSE Chemistry Paper-1: Specimen Questions with Answers 35 - 36 of 99

Question number: 35

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Question

The apparatus shown can be used to measure the rate of some chemical reactions.

Find reaction to measure some chemical reaction

Find Reaction to Measure Some Chemical Reaction

Which two reactions would this apparatus be suitable

For which two reactions would this apparatus be suitable?

reaction 1 AgNO3 (aq) + HCl (aq) → AgCl (s) + HNO3 (aq)

reaction 2 2H2O2 (aq) → 2H2O (I) + O2 (g)

reaction 3 MgO (s) + 2HCl (aq) → MgCl2 (aq) + H2O (I)

reaction 4 ZnCO3 (s) + 2HCl (aq) → ZnCl2 (aq) + CO2 (g) + H2O (I)

Choices

Choice (4) Response

a.

1 and 3

b.

2 and 4

c.

3 and 4

d.

1 and 2

Answer

b.

Explanation

This type of apparatus is used so that the gas can be collected in the syringe and the quantity can be measured from the same. In the above reactions Oxygen can be collected in the syringe and in the second reaction carbon di oxide can be collected.

Question number: 36

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Question

When pink cobalt (II) chloride crystals are heated they form steam and a blue solid. When water is added to the blue solid, turns pink and becomes hot.

Which terms describe the pink cobalt (II) chloride crystals and the reactions?

Choices

Choice (4) Response

a.

pink cobalt (II) chloride = Aqueous and reactions = irreversible

b.

pink cobalt (II) chloride = Hydrated and reactions = reversible

c.

pink cobalt (II) chloride = Hydrated and reactions = irreversible

d.

pink cobalt (II) chloride = Anhydrous and reactions = reversible

Answer

b.

Explanation

The hydration reaction may be represented by the following chemical reaction:

Reaction of pink cobalt (II) chloride crystals when heated

CoCl2. 6H2O (heat) - > CoCl2 + 6 H2O

When water is added to the blue solid

CoCl2 + 2H2O - > CoCl2. 2 H2O

Purple

CoCl2. 2H2O + 4 H2O - > CoCl2. 6 H2O

Pink

As the humidity increases further, the crystal structure again changes, this time rearranging itself to let four more water molecules in to surround each cobalt atom, forming the hexahydrate. Chemists use the raised dot symbol before the H2O to indicate the number of water molecules that have become incorporated into a compound at the atomic level. Heating the hydrated forms of cobalt chloride reverses the reactions above, returning cobalt chloride to the blue, water-free, or anhydrous, state. Water is “liberated” in these reactions, known as dehydration reactions.