1.7- practical: investigate the solubility of a solid in water at a specific temperature

A procedure used to measure the solubility of potassium nitrate in water at 40⁰C:

1.     Heat a boiling tube of water to just above 40⁰C

2.     Add Potassium nitrate to the boiling tube water and stir rapidly until no more of it will dissolve and there is undissolved solid left over in the tube.

3.     Allow this solution to cool to exactly 40⁰C, and pour off some of the solution into a weighed evaporating basin (no solid poured)

4.     Weigh the evaporating basin with its contents

5.     Heat the basin and contents gently to evaporate off all the water.

6.     When all the water seems to be evaporated weigh the evaporating basin and contents.

7.     Heat the contents again then reweigh. This makes sure all the water has evaporated (heating to constant mass)

Then work out the mass of the solvent(water) and mass of the solute (potassium nitrate crystals). To work out the solubility of potassium nitrate at 40⁰C per 100g of water, use the equation:

Solubility(g/100g) = mass of solute/mass of solvent  100