Question

1. (2d) From mixing NaHSo3 with HCl and then adding K2Cr2O7. Write the balanced half-reation equation for the reduction of the dichromate ion, Cr2)7 (2-) in acid solution.

2. (2c) From mixing NaHSO3 and adding Br2. When Br2 is reduced the product is Br-. Write the half-reaction for the reduction of Br2. Say what is oxidized to for what and what is reduced to form what.

3. (2b) From mixing NaHSO3 to H2O2. The product formed by the reduction of H2O2 is H2O. Write the balanced half-reation equation for the reduction of H2O2. Say what is oxidized to for what and what is reduced to form what.

Answer 1

1)   2d)

   Cr2O7-2 (aq) + 14 H+ (aq) + 6e- -----------------------> 2 Cr+3(aq) + 7 H2O (l)

2) 2c)   Br2 + 2e- ------------------> 2Br-

           oxidised form ------------> Br2

           reduced form ------------> Br-

3) 2b) H2O2 + 2H+   + 2e- ----------------------> 2 H2O

oxidised form ------------------->H2O2

reduced form ------------------> H2O