CPrac O - TS

Describe chemistry for Add K1 to CuSO4 → add Na2S2O3

Redox reaction occurs.

Cu2+ is reduced to CuI, a white ppt. and I− ions are oxidised to aq I2, a brown solution.

2Cu2+ + 4I− → 2CuI + I2

Redox reaction occurs. I2 is reduced to form colourless I− ions.

I2 + 2S2O32− → 2I− + S4O6

Describe chemistry for Add NH4VO3 to Zn until there is no further change

Since E(Zn2+|Zn) is less +ve than

E(VO2+|VO2+), E(VO2+|V3+) and E(V3+|V2+) 

Zn reduces VO2+ (yellow) to VO2+ (green), V3+ (blue) and V2+ (violet) sequentially.

2VO2+ + Zn + 4H+ → Zn2+ + 2VO2+ + 2H2O

2VO2+ + Zn + 4H+ → Zn2+ + 2V3+ + 2H2O

2V3+ + Zn → Zn2+ + 2V2+

Describe observation for Add NH4VO3 to Zn until there is no further change

Solution turns from yellow to green to blue and finally to violet

Describe observation for Add CuSO4 to concentrated HCI

Solution turns green then yellow

Describe chemistry for Add CuSO4 to concentrated HCI

Ligand exchange occurs when H2O in blue complex Cu(H2O)62+ is replaced by Cl− ligands to form yellow complex CuCl42−

Cu(H2O)62+ + 4Cl− ⇌ CuCl42− + 6H2O

• Cu2+ ions undergo precipitation with OH− to form Cu(OH)2, blue ppt. 

• Ionic product of Cu(OH)2 > Ksp