Question

Deduce the anion present in the salt. Assume that the reagent is added to simple salt: -

Test: -
Concentrated sulphuric acid and manganese(IV) oxide were added to the solid. On warming, a gas was evolved. It turned litmus colourless.

Is there something wrong with the question?

Answer 1

I don't think MnO2 will oxidize H2SO4 to a higher state and I virtually certain that MnO2 can't be oxidized to MnO4^- this way; therefore, the salt must be responsible for the action on the litmus paper. I think a chloride ion probably is the anion and the MnO2 oxidized the Cl^- in an acid medium to Cl2 and that acted as a bleach. H2SO4 + a salt such as NaCl or KCl readily produces HCl and a mixture of HCl and MnO2 I believe will produce Cl2 gas. Check me out on that. It's been a while since I did this in the lab. I THINK this can be used as a convenient method for the preparation of Cl2 in the lab although I always did mine by KClO3 + concd HCl + H2O to make chlorine water.