Question

13.
State reasons for the following statements :
(1) Stain of curry on a white cloth becomes reddish brown when soap is scrubbed on
it and turns yellow again when the cloth is washed with plenty of water
(ii) Curd should not be kept in copper or brass vessels. What is done to protect?​

Answer 1

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State the reasons for above observations.

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(i) Curry contains turmeric which acts as an acid - base indicator. Soap is basic in nature. Turmeric turns reddish brown. On washing with plenty of water, reddish brown product is removed and yellow turmeric is left.

(ii) Curd is acidic and attacks the copper or brass to form toxic compounds and makes it unfit for consumption. To protect copper or brass, vessels should be coated with a thin layer of tin which prevents the action of acid on copper or brass.

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Answer 2

Answer:

i) Turmeric reacts with sodium hydroxide present in soap to form red coloured compound.It turns yellow again because sodium hydroxide becomes very dilute on adding lot of water and reaction stops

ii) Curd contains lactic acid which reacts with copper or brass vessel and taste changes to prevent this this curd is kept in steel,glass or ceramic container which does not react with lactic acid present in it

Explanation: