IGCSE Chemistry Paper-1: Specimen Questions with Answers 35 - 36 of 99
Question number: 35
Question
The apparatus shown can be used to measure the rate of some chemical reactions.
Find Reaction to Measure Some Chemical Reaction
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
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.