Question

Ozone when reacts with potassium iodide solution liberates certain product, which turns starch paper blue. The liberated substance is

• A. oxygen
• B. iodine
• C. hydrogen iodide
• D. potassium hydroxide

Hint:

Iodine gives blue colour with starch.

Answer 1

The Correct Option is B

The reaction of ozone (\( \text{O}_3 \)) with potassium iodide (\( \text{KI} \)) solution is a well-known chemical process. The process can be described by the following chemical equation:

\(2 \text{KI} + \text{O}_3 + \text{H}_2\text{O} \rightarrow 2 \text{KOH} + \text{I}_2 + \text{O}_2\)

From this equation, the products are potassium hydroxide (\( \text{KOH} \)), iodine (\( \text{I}_2 \)), and oxygen (\( \text{O}_2 \)). Among these products, iodine (\( \text{I}_2 \)) is responsible for turning starch paper blue.

Here's why: Starch paper contains starch, which forms a blue-black complex when iodine interacts with it. This reaction is commonly used as a qualitative test for the presence of iodine.

Let's evaluate each option given:

• Oxygen: Oxygen is a gas that does not produce any color change on starch paper. Therefore, this option is incorrect.
• Iodine: Iodine reacts with starch paper to give a blue color, which matches the outcome described in the question. Thus, this is the correct answer.
• Hydrogen Iodide: Hydrogen iodide is not a product in this reaction. Therefore, this option is incorrect.
• Potassium Hydroxide: While this is a product of the reaction, it does not react with starch paper to produce a blue color. Hence, this option is incorrect.

Therefore, the substance liberated during the reaction that turns starch paper blue is iodine (\( \text{I}_2 \)).