Question

Few people these days print photographs in paper. To develop a film, a mix of various chemicals are used through the photographic process. In the final step, a fixer stabilises the image on paper by removing the unexposed silver salt (AgX, usually a bromide). This is achieved by treating the film or paper with a solution of thiosulphate salt (of sodium or ammonium). If not used, the excess AgX would darken and fog the image~! An old sodium thiosulphate (Na2S2O3,158.2 g/mol) is labelled 0.243. To verify this, during a redox titration of 0.151 L of this solution 41.68 mL of 0.238 M iodine solution were needed to reach the equivalence point. How pure is the sodium thiosulphate solution? Express your answer as a %.

Answer 1