Question

A student used 20 ml of 10% potassium iodide rather than 15 ml of 10% potassium iodide. What is the effect of this increase in potassium iodide on the calculated % NaOCl in the bleach?

a) Increase in % NaOCl
b) Decrease in % NaOCl
c) No effect on % NaOCl

Answer 1

Using 20 ml of 10% potassium iodide instead of 15 ml would likely cause an increase in the calculated % NaOCl in the bleach, because the excess reagent would require more sodium thiosulfate in titration.

Step-by-step explanation:

When a student uses a larger volume of 10% potassium iodide (20 ml instead of 15 ml) in a reaction mixture for determining the concentration of NaOCl in bleach, the result would likely be an increase in the calculated % NaOCl. Since the potassium iodide is present in excess, using more of it would generate more iodine (I3−). A larger volume of sodium thiosulfate would be needed to titrate the increased amount of iodine, thus suggesting that there was more NaOCl present than there actually is, leading to an overestimation.