Question

What is starch iodide paper? What happens when chlorine gas is passed through it? Give the reaction involved.

Answer 1

Starch iodide paper is a test paper impregnated with potassium iodide (KI) and starch, commonly used to detect the presence of oxidising agents.

When chlorine gas (Cl₂) is passed over moist starch iodide paper, it oxidises the potassium iodide to release iodine (I₂), which then reacts with the starch to turn the paper blue-black.

Reactions Involved:

\[ \text{Cl}_2\text{ (g)} + 2\text{KI}\text{ (aq)} \longrightarrow 2\text{KCl}\text{ (aq)} + \text{I}_2\text{ (s)} \]

\[ \text{Starch} + \text{I}_2 \longrightarrow \text{Blue-Black Complex} \]