Chem Test MC 唔該解釋~因為我唔識

2007-08-11 3:11 am

1. Which of the following would produce a solid product when reacted with dilute sulphuric acid?
A. ammonia solution
B. calcium chloride solution
C. iron (III) nitrate solution
D. copper (II) nitrate solution
2. The formula of hydrated zinc sulphate is ZnSO4‧xH2O. On strong heating, 18.7g of the hydrated sulphate produces 8.19g of water. What is the value of x?
A. 5
B. 6
C. 7
D. 8
唔該show埋第2題的step同埋解釋一下第1題的答案. THX~!

回答 (1)

Uncle Michael

2007-08-11 4:18 am

✔ 最佳答案

1. The answer is B.

A is incorrect.
Dilute sulphuric acid reacts with ammonia solution to give ammonium hydrogensulphate solution and ammonium sulphate solution.
NH3(aq) + H2SO4(aq) → NH4HSO4(aq)
2NH3(aq) + H2SO4(aq) → (NH4)2SO4(aq)

B is correct.
Dilute sulphuric acid react with calcium chloride solution to give calcium sulphate precipitate.
CaCl2(aq) + H2SO4(aq) → CaSO4(s) + 2HCl(aq)
or Ca2+(aq) + SO42-(aq) → CaSO4(s)

C is incorrect.
Dilute sulphuric acid does not react with iron(III) nitrate solution.

D is incorrect.
Dilute sulphuric acid does not with copper(II) nitrate solution.

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2. The answer is C.

In 18.7 g of ZnSO4·xH2O :
Mass of H2O = 8.19 g
Mass of ZnSO4 = 18.7 - 8.19 = 10.51

Molar mass of ZnSO4 = 65.4 + 32.1 + 16x4 = 161.5 g mol-1
Molar mass of H2O = 1x2 + 16 = 18 g mol-1

Mole ratio ZnSO4 : H2O
(10.51/161.5) : (8.19/18) = 1 : x
(10.51/161.5)x = (8.19/18)
Hence x = 7

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