Question

Describe laboratory method of preparation of sulphur dioxide giving chemical equations. Give chemical equations of the reactions of sulphur dioxide with potassium permanganate and lime water.

Answer 1

(i) In laboratory, reaction of sulphite with dilute sulphuric acid gives sulphur dioxide as:

${SO}_3^{2-}\left(aq\right)+2H^{+}\left(aq\right)\to H_{2}O\left(l\right)+{SO}_2\left(g\right)$

(ii) Cu turnnings are heated with conc. sulfuric acid.
$Cu+2H_{2}S{O}_4(conc.)\stackrel{\text{heat}}{\to }CuS{O}_4+S{O}_2+2H_{2}O$

Reaction with potassium permanganate: decolorization of pink permanganate solution.

${5SO}_2+2Mn{O}_4^{-}+{2H}_{2}O\to 5S{O}_4^{2-}+4H^{+}+2{Mn}^{2+}$

Reaction with limewater- occurs in boiling solution

${SO}_2+Ca{\left(OH\right)}_2\to {CaSO}_3\downarrow +H_{2}O$