State what are oxidising and reducing agents. Give examples of oxidising and reducing agents in the gaseous, liquid and solid form. Give two tests each generally answered by oxidising and reducing agents respectively.

Oxidizing Agents :

• Loses oxygen or electronegative radical
• Gains hydrogen or electropositve radical
• Accepts electrons.

Examples:

• Gases - O₂, O₃, Cl₂, F₂
• Liquids - H₂O₂, K₂Cr₂O₇ [acidified], conc. HNO₃, conc. H₂SO₄
• Solids - MnO₂, HgCl₂, PbO₂, KNO₃

Reducing Agents :

• Gains oxygen or electronegative radical
• Loses hydrogen or electropositive radical
• Donates electrons.

Examples:

• Gases - H₂, CO, SO₂, NH₃
• Liquids - HCl, HBr, H₂SO₃, HNO₂
• Solids - Carbon [coke], metals [K, Na, Ca], Sugar [C₁₂H₂₂O₁₁], SnCl₂

Test for an Oxidizing Agent :

• Decomposes to give a colourless gas which rekindles a glowing splint.
• Liberates chlorine on heating with conc. HCl

Test for a Reducing Agent :

• On reaction with iron[III] salts - the colour changes from yellowish brown to light green [iron [II] ions are formed].
• Liberates nitrogen dioxide on heating with conc. HNO₃.