A bag of road salt

CHEMISTRY · Multi-part · A Level · Chemistry · Oxidation, reduction and redox reactions · Oxidation, reduction and redox reactions

Problem

A bag of road salt, used to melt ice and snow from roads, contains a mixture of calcium chloride,

\text{CaCl}_2

, and sodium chloride,

\text{NaCl}

. A

2.765\text{ g}

sample of the mixture was analysed by first converting all the calcium into calcium oxalate,

\text{CaC}_2\text{O}_4

. This was then dissolved in

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

and titrated with

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

\text{KMnO}_4

solution. The titration required

24.65\text{ cm}^3

\text{KMnO}_4(\text{aq})

and produced

\text{Mn}^{2+}(\text{aq})

\text{CO}_2(\text{g})

, and

\text{H}_2\text{O}(\text{l})

. (a) What would be observed at the equivalence point of the titration? (b) Write the half-equation for the oxidation reaction, starting with

\text{C}_2\text{O}_4^{2-}

. (c) Write the half-equation for the reduction reaction, starting with

\text{MnO}_4^-

. (d) Write the overall equation for the redox reaction. (e) Determine the number of moles of

\text{C}_2\text{O}_4^{2-}

. (f) Deduce the number of moles of

\text{Ca}^{2+}

in the original sample. (g) What was the percentage by mass of

\text{CaCl}_2

in the road salt?