To measure the temperature at which different masses of solute will dissolve in a known volume of solvent, and hence plot a solubility curve.
Method: (Source: Classic Chemistry Experiments, RSC)
The method below works by cooling a solution, and measuring the temperature at which crystals just start to form. This is the temperature at which the solution became saturated, and so this temperature, and the mass of solute you used, form one point on the curve. More water can then be added to redissolve the crystals, and the experiment repeated to get enough points to draw the curve.
- Add 2.6g of ammonium chloride crystals to 4cm3 (4g) of water in a boiling tube.
- Heat mixture in hot water bath until all the solute dissolves.
- Cool in an ice bath until crystals just start to appear – record temperature.
- Calculate and record the solubility at this temperature (g per 100g of water) i.e. 2.6g × 100/volume of water = 65g per 100g of water.
- Add 1cm3 (1g) of water to the boiling tube.
Repeat steps 2 – 5 until sufficient points have been obtained to plot solubility curve.