When a blue crystal is heated in a test tube, it becomes a white compound. When two drops of water are added to the white compound it again becomes blue crystal. Identify the blue crystal and explain the above observations with the aid of chemical equations.
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Answered by
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Bonjour!
The blue crystal is hydrated copper sulphate.
CuSO4•5H2O ––Heat––» CuSO4 + 5H2O
CuSO4 + 5H2O –––» CuSO4•5H2O
The blue crystal is hydrated copper sulphate.
CuSO4•5H2O ––Heat––» CuSO4 + 5H2O
CuSO4 + 5H2O –––» CuSO4•5H2O
Answered by
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Heating of Copper Sulphate
Materials Required:
Lab Procedure:
Take a small amount of copper sulphate crystals in a dry boiling tube.
Hold the boiling tube with a test tube holder.
Heat the boiling tube over the flame of a burner first gently and then strongly.
Observe the colour of copper sulphate crystals after heating for some time.
Note the water droplets along the sides of the boiling tube.
Remove the boiling tube from the flame and cool.
Add 2-3 drops of water on the sample of copper sulphate obtained after heating.
Observations:
On heating, the colour of copper sulphate crystals changes from blue to white.
There are water droplets on the walls of the boiling tube.
On adding 2-3 drops of water white copper sulphate turns blue.
Inferences:
Copper sulphate crystals contain water of crystallisation (CuSO4.5H2O).
On heating, hydrated copper sulphate loses its water molecule and forms white coloured anhydrous copper sulphate.
On adding water anhydrous copper sulphate changes to hydrated copper sulphate.
It is a reversible chemical change.
Precautions:
Keep the mouth of the test tube away from your face and also from other classmates.
Always use test tube holder while heating the test tube.
Take a small quantity of copper sulphate crystals.
Materials Required:
Lab Procedure:
Take a small amount of copper sulphate crystals in a dry boiling tube.
Hold the boiling tube with a test tube holder.
Heat the boiling tube over the flame of a burner first gently and then strongly.
Observe the colour of copper sulphate crystals after heating for some time.
Note the water droplets along the sides of the boiling tube.
Remove the boiling tube from the flame and cool.
Add 2-3 drops of water on the sample of copper sulphate obtained after heating.
Observations:
On heating, the colour of copper sulphate crystals changes from blue to white.
There are water droplets on the walls of the boiling tube.
On adding 2-3 drops of water white copper sulphate turns blue.
Inferences:
Copper sulphate crystals contain water of crystallisation (CuSO4.5H2O).
On heating, hydrated copper sulphate loses its water molecule and forms white coloured anhydrous copper sulphate.
On adding water anhydrous copper sulphate changes to hydrated copper sulphate.
It is a reversible chemical change.
Precautions:
Keep the mouth of the test tube away from your face and also from other classmates.
Always use test tube holder while heating the test tube.
Take a small quantity of copper sulphate crystals.
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