Redox balancing question?

Question

Br2 reacts under acid conditions with (S2O3)-2 (aq) to give HBr, (SO4)-2 and H+. The number of moles of Br2 which reacts with one mole of (S2O3)-2 is?

(charge is given outside the brackets)

Answer 1

Br2 reacts under acid conditions with (S2O3)-2 (aq) to give HBr, (SO4)-2 and H+. The number of moles of Br2 which reacts with one mole of (S2O3)-2 is?

Br2 (has 2Br's @ zero charge each) takes 2 e-   --> 2 HBr (2 Br-1 's)

(S2O3)-2  (2 S's @ +4 total) --> 2 (SO4)-2  (2S @ +12 total) & 8 e- lost

to balance the electrons taken & lost, we 4 times the Br2:

4 Br2 &  takes 8 e-   --> 8 HBr

1 (S2O3)-2   --> 2 (SO4)-2  & 8 e- lost

now we combine them:

4 Br2 &  1 (S2O3)-2   --> 8 HBr  &    2 (SO4)-2

adding the H+ 's to balance the charges, we preesntly have -2 on the left & -4 on the right, so we will add 2H+ 's to the right, so that it is -2  -->   -2  :

4 Br2 &  1 (S2O3)-2   --> 8 HBr  &    2 (SO4)-2  & 2 H+

now to balance the H's , using water:

4 Br2 &  1 (S2O3)-2  &  5H2O  --> 8 HBr  &    2 (SO4)-2  & 2 H+

every molecule has its # of moles, we save oxygen to the last as a check on our work,  it showed already be balanced if we are correct.

8 oxygens -->  8 oxygens

it is done, your answer is:

4 Br2 &  1 (S2O3)-2  &  5H2O  --> 8 HBr  &    2 (SO4)-2  & 2 H+

& your answer to:

The number of moles of Br2 which reacts with one mole of (S2O3)-2 is:

4 Br2  & 1 (S2O3)-2