Problem

Sodium nitrate(III),

\text{NaNO}_2

, is used as a preservative in processed meat. In an acidic solution, nitrate(III) ions,

\text{NO}_2^-

, are converted to nitric(III) acid,

\text{HNO}_2

, which reacts with the manganate(VII) ion. A 1.00 g sample of a water-soluble solid containing

\text{NaNO}_2

was dissolved in dilute

\text{H}_2\text{SO}_4

and titrated with

0.0100\ \text{mol dm}^{-3}

aqueous

\text{KMnO}_4

solution. In the reaction,

\text{NO}_2^-

is oxidized to

\text{NO}_3^-

. The titration required

12.15\ \text{cm}^3

of the

\text{KMnO}_4

solution. Calculate the percentage by mass (to 2 s.f.) of

\text{NaNO}_2

in the 1.00 g sample.