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In the treatment of domestic water supplies, chlorine is added to the water to form HCIO.
Cl2(aq) + H2O(1) ►
H(aq) + Cl(aq) + HCIO(aq)
The HCIO reacts further to give CIO ions.
HCIO(aq) + H2O(l) 7H30*(aq) + CIO (aq)
Both HCIO and C10 kill bacteria by oxidation.
What is the change in oxidation number of chlorine when forming the Cio-ion from aqueous
chlorine?
B 0
D
A-1
C +1
+2
9701/12/M/J/16
© UCLES 2016

Answer 1

The change in oxidation number = +1

Further explanation

Reaction 1

Cl₂(aq) + H₂O(I) → H⁺(aq) + Cl⁻(aq) + HClO(aq)

Reaction 2

HClO(aq) + H₂O(I) → H₃O⁺(aq) + ClO⁻(aq)

The change in oxidation number of chlorine :

From Cl₂ to ClO⁻

oxidation number Cl₂=0

oxidation number Cl in ClO⁻

`\tt Cl+(-2)=-1\\\\Cl=+1`

So the change : +1