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NCERT VIII - Sciences

One day Reeta went to a jeweller's shop with her mother. Her mother gave an old gold jewellery to the goldsmith to polish. Next day when they brought the jewellery back, they found that there was a slight loss in its weight. Can you suggest a reason for the loss in weight?


Gold is polished with the help of an acid or a chemical.First of all the goldsmith washes the gold or the ornament in the solution called aqua regia. which is able to dissolve gold so a thin layer of gold get dissolve in that solution/chemical and we find a  shiny surface because of the next layer and because the layer gets dissolved while polishing we find a slight loss in the weight of that gold ornament.
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Gold is a noble metal. It does not react with many kinds of chemicals readily.  However, it does react with chlorine and some other acids slowly.  It does dissolve in Nitric acid and Hydrochloric acid mixture called aqua regia.  It gets slowly oxidized over years. 

If copper or silver is mixed in Gold ornaments, then they do react with acidic chemicals and gases slowly.

Gold also collects some dirt and impurities over its surfaces.  In the cleaning processes, possibly  ammonia, aqua regia or some solvent is used to dissolve all impurities collected on the surface.  So a little part of gold also gets dissolved.  If Gold consists of copper also, then some copper also gets dissolved.

So during the purification or shining or polishing act, some metal of the ornaments does gets removed.  So its weight decreases.

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