CE CM questions

2008-08-31 9:47 am

85which of the following gases can be dried by anhydrous calcium chloride?
(1)oxygen
(2)chlorine
(3)ammonia

86Which of the following compounds does not form a solid oxide when headed strongly?
A. copper(II) sulphate B. lead(II) carbonate
C. potassium nitrate D. calcium hydroxide

89If a glass reagent bottle containing sodium hydroxide solution is allowed to stand in air for a few weeks, it is often difficult to remove the glass stopper due to formation of a solid round the bottle neck. The solid is probably
A. sodium oxide B.sodium peroxide
C. sodium carbonate C. sodium hydrogencarbonate

Solibility of salts containing sulphate
please refer to: http://hk.knowledge.yahoo.com/question/question?qid=7008081401236
From the ans of the third question.He said BaSO4 does not have any reaction towards any acid, and I know MgSO4 does not too. So can I say ALL salts containing sulphate are not soluble in any acids?

回答 (1)

Uncle Michael

2008-09-11 6:53 pm

✔ 最佳答案

85.
The answer is (3).

Anhydrous calcium chloride is a common drying agent. It can be used to dry all common gases except ammonia. This is because anhydrous calcium chloride can absorb ammonia by forming complex.
CaCl2(s) + xNH3(g) → [Ca(NH3)x]Cl2(s)

The equation above may be out of the present HKCEE syllabus.

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86.
The answer is C.

CuSO4(s) → CuO(s) + SO3(g)
PbCO3(s) → PbO(s) + CO2(g)
2KNO3(s) → 2KNO2(s) + O2(g)
Ca(OH)2(s) → CaO(s) + H2O(g)

This question is out of the present HKCEE syllabus.

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89.
The answer is C (sodium carbonate).

Sodium hydroxide reacts with carbon dioxide from the air to form sodium carbonate.
2NaOH + CO2 → Na2CO3 + H2O

Na2CO3 would not be further converted to NaHCO3 in the air, because the air does not contains sufficient amount of CO2.

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You have to distinguish between the terms “reaction with” and “dissolve in”.

SO42- ion does not react with acid solutions. However, most metal sulphates (e.g. MgSO4) are soluble in water, so that such metal sulphates are soluble in acid solutions. Actually, the metal sulphates are dissolved in the water of the acid solutions.
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