40. Solving a chemistry problem

10. The exact weight of the drug "Copper sulfate" weighing 0.4125 g was dissolved in a flask in 25 ml of water, 2 ml of diluted sulfuric acid, 1.5 g of potassium iodide were added and the released iodine was titrated with a solution of sodium thiosulfate (0.1 mol / l) starch. what volume of titrant was spent if the mass fraction of copper sulfate in l/s was 98.95%. Mm. copper sulfate - 249.7. Give the reaction equations underlying the definition.