Titration exercise 4

0.168 g of impure, solid sodium iodate(V) was weighed out and made up to exactly 100 cm³ in a volumetric flask. A 20.0 cm³ sample of this solution was pipetted into a conical flask. 10 cm³ of 1 M sulfuric acid (an excess) and 20 cm³ of 0.1 M potassium iodide solution (an excess) was added. This produced iodine according to the following equation:

IO₃^-(aq) + 5I^-(aq) + 6H⁺(aq) ⇒ 3I₂(aq) + 3H₂O(l)

This iodine was then titrated with 0.100M sodium thiosulfate solution. The titres were 9.70 cm³, 9.30 cm³ and 9.40 cm³.

What was the purpose of the added sulfuric acid?

What was the percentage purity of the solid sodium iodate?

Answer