Q15 of 31 Page 56

A man went from door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used ?

The solution used by the goldsmith was aqua-regia solution which contains concentrated nitric acid and concentrated hydrochloric acid in the ratio 1:3. When the gold bangles were dipped into this solution, considerable amount of gold was dissolved in it. Thus the weight of the bangle was reduced.


More from this chapter

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12

Give reasons:

(a) Platinum, gold and silver are used to make jewellery


(b) Sodium, potassium and lithium are stored under oil.


(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.


(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.

 13

You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.

 14

Differentiate between metals and non-metals on the basis of their chemical properties.

 16

Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).