HKDSE-onward Chemistry Question Review

學術區
81

Question:

Consider the reaction below:

SO_3^{2-} + S \to S_2O_3^{2-}

What condition is missing?

82

Solution:

Heat. S is in excess.

83

Question:

Thiosulphate ions will decolourize an aqueous Iodine solution. Write out the ionic equation for this reaction.

84

Solution:

2S_2O_3^{2-} (aq) + I_2 (aq) \to S_4O_6^{2-} (aq)+ 2I^{-} (aq)

85

Question:

Draw the Tetrathionate anion.

86

Solution:

ODL
ODL312×200 3.78 KB

87

Question:

What anion can be easily found in paints and pigments?

88

Solution:

Sulphate(VI) ions

89

Question:

What reducing agents can be used to break down the peroxy bond in persulphate ions?

90

Solution:

Iodine and Manganese(II) ions

S_2O_8^{2-} (aq) + I_2 (aq) \to 2SO_4^{2-} (aq) + 2I^- (aq)

S_2O_8^{2-} (aq) + Mn^{2+} (aq) + 2H_2O (l) \to 2SO_4^{2-} (aq) + 4H^+ (aq) + MnO_2(s)

91

Question:

What is the nature of the below redox reactants?

(a) FeCl_3 + H_2S
(b) S_2O_3^{2-} + 2H^+

92

Solution:

(a) Reduction of Fe^{3+} ions
(b) Disproportionation

Both reactions will produce sulphur solids.

93

Question:

Name 2 common sulphur ores.

94

Solution:

Iron(III) pyrite Fe_2S_3
Zinc blende ZnS

95

Question:

Suggest a common industrial method to remove:

(a) Moist
(b) Dust

96

Solution:

(a) H_2SO_4 (l)
(b) Electrostatic precipitator.

97

Question:

When heating FeSO_4, both SO_2 and SO_3 will be liberated but Fe_2(SO_4)_3 not. Explain briefly.

98

Solution:

Fe_2(SO_4)_3, upon heating, will liberate SO_2 and O_2. From this, we can say that in FeSO_4, upon heating, Fe^{2+} ion will reduce O_2 originally liberated into sulphur oxides.

99

Question:

Some say that the oxidation number of Fe_3O_4 is +\frac{8}{3}. Prove that he is on9.

100

Solution:

Fe_3O_4 = FeO + Fe_2O_3

So it is a mixture.