Question

1) How many electrons are transferred in the following reaction:

4 Fe + 3 O2 = 2 Fe2 O3

a) 8

b) 12

c) 10

d) 6

e) 3

2) In thus unbalanced chemical reactiion, which element is oxidized and which is reduced?

Cl2 + NaBr = NaCl + Br2

a) sodium is reduced, chlorine is oxidized

b) chlorine is reduced, sodium is oxidized

c) chlorine is oxidized, bromine is reduced

d) bromine is oxidized, chlorine is reduced

Answer 1

1)

oxidation state of Fe changes from 0 in reactant to +3 in Fe2O3

So, each atom of Fe is releasing 3 electrons

There are 4 Fe taking part in this reaction.

So,

number of electrons transferred = 3*4 = 12

Answer: b

2)

Oxidation state of Na is +1 in NaBr and NaCl

So, Na is neither oxidised nor reduced

oxidation state of Cl changes from 0 in reactant to -1 in product

So, Chlorine is reduced

oxidation state of Br changes from -1 in reactant to 0 in product

So, Bromine is oxidised

Answer: d