why the appearance of some metals is dull before rubbing them?
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Metals lose their shine or brightness on keeping in air for a long time and acquire a dull appearence due to the formation of a thin layer of oxide, carbonate or sulphide on their surface by the slow action of various gases present in air.
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Metals like iron, copper, magnesium, sodium are reactive metals. These metals react with oxygen and form its oxide on the outer layer. Metal oxides are dull in colour. As a result, the metal loses his lustrous property.
e.g. Iron forms a brown layer which we call rusting of iron; aluminium forms smoke colour aluminium oxide; copper form black and green layer with oxygen and sulphur etc.
When we rub the metals with sandpaper, its outer oxide layer is scrapped out.
You may recall the burning of magnesium in chapter one. here we first clean the magnesium ribbon. It was because magnesium oxide interferes in burning
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e.g. Iron forms a brown layer which we call rusting of iron; aluminium forms smoke colour aluminium oxide; copper form black and green layer with oxygen and sulphur etc.
When we rub the metals with sandpaper, its outer oxide layer is scrapped out.
You may recall the burning of magnesium in chapter one. here we first clean the magnesium ribbon. It was because magnesium oxide interferes in burning
Hii ✌️
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