Question

According to the balanced equation below, how many moles of `ClO^-2 (aq)` are needed to react completely with 20. mL of 0.20 M `KMnO_4` solution?

`2H_2O(l) + 4MnO_4(aq) + 3ClO_2^(-)(aq) -> 4MnO_2(s) + 3ClO_4^(-)(aq) + 4OH^(-)(aq)`

Answer 1

`3*mmol` `"chlorite anion"` are required.

Explanation:

`"Reduction"`
`MnO_4^(-) +4H^(+) + 3e^(-) rarr MnO_2(s) + 2H_2O(l)` `(i)`

`"Oxidation"`
`ClO_2^(-) +2H_2O rarr ClO_4^(-) + 4H^+ +4e^-` `(ii)`

`"Overall"` `4xx(i) +3xx(ii)`
`4MnO_4^(-) +3ClO_2^(-) +4H^+rarr 4MnO_2(s) +3ClO_4^(-)+ 2H_2O(l)`

`"Moles of "KMnO_4=20xx10^-3Lxx0.20*mol*L^-1=4.0xx10^-3*mol`

Given the equation, we need 3/4 equiv of chlorite anion,

`3/4xx4.0xx10^-3*mol`

What would you observe in this reaction? What was the macroscopic colour change?