F.5Chem Redox MC 40

1)What is the oxidation number of manganese in Mn(NH3)4Cl2?
A. -2
B. 0
C. +2
D. +4

The answer is: C. +2

Total oxidation number of NH3 = 0
Oxidation number of Cl = -1

Total oxidation number of Mn(NH3)4Cl2 = 0
(Oxidation number of Mn) + 4(0) + 2(-1) = 0
Hence, oxidation number of Mn = +2


=====
2)X is an aqueous solution. When X is added in excess to bromine water, the resulting solution is colourless. When X is treated with dilute hydrochloric acid, a gas with an irritating smell evolves. X may be
A. sodium sulphite solution
B sodium hudroxide solution
C ammonium hydrogencarbonate solution
D ammonium sulphate solution

The answer is: A. sodium sulphite solution

A: Sodium sulphite is a reducing agent, which can reduce brown bromine water to colourless bromide ions. It can also react with dilute hydrochloric acid to give sulphur dioxide gas which has an irritating smell.

B: Sodium hydroxide reacts with brown bromine water to give colourless sodium bromide solution and colourless sodium bromated solution. However, no gas is formed when sodium hydroxide reacts with hydrochloric acid.

C: Ammonium hydrogencarbonate solution cannot decolorize brown broimine water. It can react with hydrochloric acid to give carbon dioxide gas which does not have an irritating smell.

D: Ammonium sulphate solution cannot decolorize brown broimine water. Besides, it does not react with hydrochloric acid.


=====
3) Chlorine is bubbled into an aqueous solution P for some time. The colour of P gradually changes to brown. P is NOT likely to be
A calcium hydroxide solution
B potassium iodide solution
C iron(ll) chloride solution
D Zinc bromide solution

The answer is: A calcium hydroxide solution

A: Calcium hydroxide react with calcium hydroxide solution to give colourless calcium chloride solution and colourless calcium hypochlorite solution.

B: Chlorine oxidizes iodide ions to brown iodine solution.

C: Chlorine oxidizes iron(II) ions to brown iron(III) ions.

D: Chlorine oxidizes bromide ions to brown bromine ions.

2010-11-05 00:16:17 補充：
3. A should be:

A: Calcium hydroxide react with calcium hydroxide solution to give colourless calcium chloride solution and colourless calcium hypochlorite solution.

Calcium hydroxide react with calcium hydroxide solution to give colourless calcium chloride solution and colourless calcium hypochlorite solution.
A typing error.