Oxidizing Agents

• Common used oxidizing agents include;
• KMnO₄
• K₂CrO₇
• H₂O₂
• *usually requires acidic conditions eg adding sulphuric acid before carrying out the test except MnO₄ requires alkaline conditions.

 

i)Potassium Permanganate

• KMnO₄(aq)- purple
• used to detect Fe²⁺(aq) in acidic medium.

Test	Observation	Notes
add dil H2SO4 followed by KMnO4(aq)	KMnO4 is decolourised	Fe2+ is oxidised to Fe3+ and MnO4–(aq) is reduced to Mn2+(aq)

ii)Oxidation of iodide ions

• I^– ions are oxidised to yellowish brown iodine(aq)
• MnO₄^–(aq) are reduced to faint pink Mn²⁺(aq)

 

iii)Oxidation of hydrogen peroxide

• MnO₄^–(aq) oxidize H₂O₂ to water and oxygen
• MnO₄^–(aq) are reduced to faint pink/colourless Mn²⁺(aq)

 

iv)Oxidation of Ethanol

• it is oxidized in alkaline medium to ethanoic acid
• MnO₄^–(aq) are decolourised

 

K₂Cr₂O₇(aq)-orange

• stabilized by an acidic environment.
• acts as an oxidizing agent, while it is reduced to green Cr³⁺
• like MnO₄^– ions, dichromate ions oxidize;

• Fe(ii) to Fe(iii)- dirty green observed due to mixture of green & yellowish brown;
• I^– ions to I₂;
• H₂O₂ to H₂O & O₂
• Dichromate ions oxidize sulphite ions to sulphate and nitrate ions to nitrate.
• Ethanol can be used to test for dichromate(vi) ions- the sln turns to green

 

Hydrogen peroxide (H₂O₂)

• colourless
• can work in both acidified and alkaline medium.
• it is reduced to water and there is no O₂(g) that is liberated
• oxygen is liberated only when it is acting as a reducing agent

The table below shows the observations and deductions made when H₂O₂(aq) is added to a test substance containing some cations and anions;

Observations	Deductions	Notes
Solutions turns red-brown from pale green	Fe(ii)(aq) present	Fe(ii)(aq) is oxidized to Fe(iii)(aq)
Solutions turns dark brown & black-brown ppt from pale pink	Mn2+(aq) prsent	Oxidation of Mn2+ to MnO2(s)
Solution changes from colourless to orange-brown; a black ppt settles at the bottom after a few minutes	I–(aq) present	I– is oxidized to I2(s). black ppt are crystals of iodine(s). orange-brown sln consists of I3-(aq)

Reducing Agents