Question

Q. I Complete the table Oil stains are seen when rubbed om food items Gives thug black Gives puople colour colour when When 2 drops of iodine solution copper sulphate is added solution & 10 doops of caustic soda is added to it, paper.

• Raw Potato
• Dried coconut
• Peanuts Milk
• Gram flour
• Boiled rice​

Answer 1

Answer:

Correct option is

B

(i) and (iii)

If starch is mixed with iodine, it gives a blue-black colour.

The 'boiled and mashed potato' and a 'slice of bread' contain starch and all other options are not containing starch. So, 'boiled and mashed potato' and a 'slice of bread' will give blue-black colour when it tested with iodine.

The correct answer is option (b).

Explanation:

(a) The natural indicator present in curry stain is turmeric.

(b) The yellow stain of curry turns reddish-brown when soap is scrubbed on it because of the fact that soap solution is basic in nature which changes the colour of turmeric in the curry stain to reddish-brown. This stain turns yellow again when the cloth is rinsed with water because then the basic soap gets removed with water.

(c) The nature of soap is basic.

Answer 2

When we mix starch with iodine it gives a blue-black colour.

raw potato and boiled rice contains starch due to which a deep blue colour occurs.

• Amylose in starch is responsible for the formation of a deep blue color in the presence of iodine
• Amylose in starch is what causes the dark green color in the presence of iodine.
• The iodine molecule slides inside  the amylose coil.
• Iodine Reagent - KI: Iodine is not very soluble in water, so Iodine reagent is made by dissolving iodine in water in the presence of potassium iodide.
• This causes a complex of soluble straight-chain triiodide ions to slip into the coil of the starch causing a dark blue-black color.

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