Q68 / 180 · AIIMS 2006 · Chemistry

Assertion : In the iodometric titration starch is used as an indicator. Reason : Starch is a polysaccharide.

  • A
    If both assertion and reason are true and reason is the correct explanation of the assertion
  • Correct answer
    B
    If both assertion and reason are true but reason is not the correct explanation of the assertion
  • C
    If assertion is true, but reason is false
  • D
    Both assertion and reason are false statements.

Solution

Starch $\left(\mathrm{C}_6 \mathrm{H}_{10} \mathrm{O}_5\right)_n$ is a polysaccharide. It consists of two fractions - one is known as $\alpha$ amylose and the other is $\beta$-amylose or amylopectin. In iodimetric and iodometric titrations, starch solution is used as an indicator. It gives blue or violet colour with free iodine. At the end point the blue or violet colour disappears when iodine is completely changed to iodide.

Hence, the correct answer is option: 'B'.

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