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| 1. |
Color of copper sulphate crystal changes on heating? Give reason |
| Answer» (1) The colour of the compound before heating is blue, and after heating is white-grey.(2) Copper sulphate is basically a hydrated salt which contains 5 molecules of water of crytsallisation, and so is denoted by the chemical formula CuSO45H2O. These 5 molecules of water of crytsallisation are responsible for the blue colour of the salt. However, when copper sulphate is heated for some time, the blue colour disappears and it becomes white-gray in colour. This is because the water molecules are lost on heating and copper sulphate pentahydrate is converted to anhydrous copper sulphate.CuSO45H2O → CuSO4 + 5H2O.(3) The original colour can be restored if anhydrous copper sulphate is left open for sometime. It combines with moisture present in air and forms copper sulphate pentahydrate again. | |