CBSE Class 12 · 2001 · All India Compartment · Redox Reactions and ElectrochemistryVery Short Answer

Electrolysis of KBr(aq) gives Br

_{2}

at the anode, but that of KF(aq) does not give F

_{2}

. Give reason for this disparity.

Solution

At the anode the species with the lower oxidation (i.e. whose couple has the lower reduction) potential is oxidised preferentially.

E^{\circ}

of the F

_{2}

^{-}

couple (+2.87 V) is the highest known — far above that of O

_{2}

_{2}

O — so in KF(aq) water is oxidised and O

_{2}

, not F

_{2}

, is evolved.
For KBr(aq), the Br

_{2}

/Br

^{-}

potential (+1.08 V) is below the practical oxidation potential of water (with overvoltage), so Br

^{-}

is oxidised and Br

_{2}

is obtained.

CBSE Class 12 Board · 2001 · All India Compartment · Subjective