1
Q
How can you investigate how temperature affects solubility?
A
- Make a saturated solution by adding an excess of ammonium chloride to 10cm³ of water in a boiling tube. You will know when ammonium chloride is in excess because it will start to sink to the bottom of the tube.
- Give the solution a good stir and place the boiling tube in a water bath set to 25°C.
- After 5 minutes, check that all of the excess solid has sunk to the bottom of the tube and use a thermometer to check that the solution has reached 25°C.
- Weigh an empty evaporating basin. Pour some of the solution into the basin, making sure not to pour in any of the undissolved solid.
- Re-weigh the basin and its contents, then gently heat it using a Bunsen burner to remove all the water.
- Once all the water has evaporated, you’re left with pure ammonium chloride. Re-weigh the evaporating basin and its contents.
- Repeat steps 1-6 twice more, but with the water bath at different temperatures (e.g. 35°C and 45°C).
- You can use the different masses to work out the solubility at each temperature. Then you are able to plot the results on a graph.
2
Q
In step 5, why should you not heat the basin too strongly?
A
If you heat the basin too strongly, some of the ammonium chloride might turn into a gas and escape. This will cause the mass of the solid in the basin to decrease, and your solubility value will be lower than it should be.
3
Q
Why should you make sure that the solute is in excess in this experiment?
A
It’s important that you make sure the solute is in excess in this experiment, so that you end up with a saturated solution. If the solution is unsaturated, this means that more solute can be dissolved in the solvent, so the calculated solubility will be less than the true value.
