Question 6 of 7intermediate🔧 ApplyShort Answer2 marks

While using iodine in the laboratory, a few drops of iodine fell on Mishti's socks and a few fell on her teacher's saree. The drops of iodine on the saree turned blue-black while the colour on the socks did not change. What can be a possible reason?

Correct Answer

The teacher's saree likely contains starch. Many fabrics, especially cotton sarees, are starched (treated with starch) to make them stiff and crisp.

When iodine fell on the starched saree, it reacted with the starch and turned blue-black.

Mishti's socks are probably made of synthetic material or have not been starched, so they do not contain starch. Therefore, the iodine did not change colour on the socks.

Exercise: Let us enhance our learning | Q: 11 | (Page Page 23)
For More Understanding

Explanation

The chapter explains in section 3.3.1 that a blue-black colour indicates the presence of starch when iodine solution is applied. This test is used to detect starch in food items. The same principle applies here—starch is often used to stiffen fabrics like cotton sarees during washing or ironing. The iodine detected the presence of starch on the saree fabric, causing the blue-black colour change.

Solution Steps

  1. The teacher's saree likely contains starch

  2. Many cotton sarees are starched to make them stiff and crisp

  3. Iodine reacts with starch to turn blue-black

  4. Mishti's socks are probably made of synthetic material or not starched

  5. Without starch, iodine does not change colour

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