Reducing Agents
- Commonly used reducing agents include;
- KI-iodides;
- Sodium thiosulphate -thiosulphate ions
Potassium Iodide, KI
- I–(aq) is oxidized to I2(aq)-brown or I2(s)-black ppt
Observations and deductions when KI is added to various test reagents
| Observations | Deductions | Notes |
|---|---|---|
| Pale solution to brown ppt plus few white ppt | Cu2+ present | Cu2+ is reduced to Cu1+ white ppt is CuI(s) |
| a bright yellow ppt soluble in excess KI to give colourless sln | Pb2+ present | yellow PbI2 dissolves in excess KI bcz a complex PbI42- is formed |
| A dark brown sln from pale red brown sln; black ppt forms slowly | Fe3+ | Fe(iii) to Fe(ii) |
| purple sln to faint pink sln | Mn2+ present | Mn7+ to Mn2+ |
Hydrogen Peroxide
- it can act as a reducing agent in some reactions
- oxygen gas is liberated, you should prepare to test for oxygen.
- examples include;
- Acidified hydrogen peroxide reduces Mn(7+) to Mn(2+)
- pH change may affect the behaviour of hydrogen peroxide in redox reactions eg;
- in acidic medium: Mn(7+) is reduced to Mn(2+)
- in alkaline medium: Mn(2+) is oxidized to Mn(4+) -dark brown ppt