Potassium iodide is a catalyst for the reaction between sodium thiosulfate and sulfuric acid. A catalyst speeds up a chemical reaction without being consumed in the reaction. In this case, the potassium iodide helps to break down the sodium thiosulfate into smaller molecules, which can then react more quickly with the sulfuric acid. As the concentration of potassium iodide increases, the rate of the reaction also increases.

Sulfuric acid (H2SO4)

Sulfuric acid is one of the reactants in the reaction between sodium thiosulfate and sulfuric acid. As the concentration of sulfuric acid increases, the rate of the reaction also increases. This is because there are more sulfuric acid molecules available to react with the sodium thiosulfate.

The overall effect of increasing the concentration of both potassium iodide and sulfuric acid is to increase the rate of the reaction. This is because the potassium iodide acts as a catalyst, which speeds up the reaction, and the sulfuric acid is one of the reactants in the reaction.