Give reasons for the following
(i) To make hot water tanks, copper is used and not steel.
(ii) Lemon is used for restoring the shine of tarnished copper decorations
(iii) Addition of some silver to pure gold for making ornaments.
Answers
Explanation:
I) Copper is used to make hot water tanks and not steel this is because the iron (in steel) is more reactive than then copper also it react with hot steam to produce ferrosoferric oxide. Due to which the body of tank will become weaker and weaker. While copper does not react with hot water.
2) The citric acid present in the lemon juice dissolved the Cooper oxide coating formed on the metal surface, thereby cleaning the metal and giving the surface of the copper decorations the characteristic metalic lustre.
3) Pure gold (or 24 carat-gold)is very soft due to which it is very difficult to to make jewellery with such gold. Therefore a very small quantity of silver (or copper) is added to it.
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Explanation:
i ) Copper is the best conductor of electricity after Siver, and it does not absorb heat faster and makes it remain hot for a long time unlike steel which absorbs heat comparatively faster...
iii) Siver is added to gold for making ornaments as silver is lustrous as well as malleable...and gives a shine to the gold jewellery for a long time...
ii) Copper does loses its lustre faster so to restore its lustre lemon is used as Copper is highly reactive to Citric acids...