Question

Explain the following:

K₂Cr₂O₇ acts as a powerful medium oxidising agent in acidic

Answer 1

1. \[\ce{Cr2O^2-_7}\] is reduced to Cr³⁺ in acidic medium; its standard potential is +1.31 V, so it has a strong tendency to gain electrons and oxidise others.
2. In acid \[\ce{K2Cr2O7 + 4H2SO4 -> K2SO4 + Cr2(SO4)3 + 4H2O + 3O}\] (nascent oxygen), which oxidises substrates.
3. One \[\ce{Cr2O^2-_7}\] accepts 6 e⁻ (high electron uptake), making it a powerful oxidiser.
4. Hence, it oxidises I⁻, Fe²⁺, \[\ce{SO^2-_3}\], H₂S, halogen acids, and is used in redox titrations.