TESTING FOR WATERTESTING FOR WATER

Lesson OutcomeLesson OutcomeThrough experimentation understand the Through experimentation understand the properties of water (ie. Water of crystallization properties of water (ie. Water of crystallization & freezing point).& freezing point).

WATER OF CRYSTALLISATIONWATER OF CRYSTALLISATION

Sometimes ionic substances crystallise from aqueous Sometimes ionic substances crystallise from aqueous solutions with the molecules of water still attached.solutions with the molecules of water still attached.

This is called This is called water of crystallisation.water of crystallisation.

It is written in the form CaSOIt is written in the form CaSO44.2H.2H22OO (calcium sulphate dihydrate)(calcium sulphate dihydrate)

Heating the solid can drive off the water, leaving the Heating the solid can drive off the water, leaving the anhydrousanhydrous (without water) ionic substance. (without water) ionic substance.

Heating Hydrated Cobalt ChlorideHeating Hydrated Cobalt Chloride

Turned to a blue powder called anhydrous Turned to a blue powder called anhydrous cobalt chloride and gave off water vapour. cobalt chloride and gave off water vapour. The blue powder gradually turned pink The blue powder gradually turned pink again when it was left standing in the again when it was left standing in the room.room.

HEATING COPPER SULPHATEHEATING COPPER SULPHATE

WHY DOES WHY DOES WHITEWHITE COPPER COPPER SULPHATE TURN SULPHATE TURN BLUEBLUE WHEN WATER WHEN WATER IS ADDED?IS ADDED?

When heated, hydrous crystals lose their When heated, hydrous crystals lose their water of crystallisation and turn into a water of crystallisation and turn into a powder. They may also lose their colour. powder. They may also lose their colour. They are then said to be anhydrous. They are then said to be anhydrous.