Investigating Solubility

Question 1

how to investigate how temperature affects solubility of ammonium chloride

Answer 1

1. 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
2. give the solution a good stir and place the boiling tube in a water bath set to 25 degrees Celsius
3. 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 degrees Celsius
4. weigh an empty evaporating basin - pour some of the solution into the basin, making sure not to pour in any of the undissolved solid
5. re-weigh the basin and its contents, then gently heat it using a Bunsen burner to remove all of the water
   NOTE: if you heat the basin too strongly, some of the ammonium chloride might turn into a gas and escape and this will cause the mass of the solid in the basin to decrease, and the solubility value will be lower than it should be
6. once all of the water has evaporated, you’ve left with pure ammonium chloride, then re-weigh the evaporating basin and its contents
7. repeat this but with the water both at different temperatures and you can use the different masses to work out solubility at each temperature

Question 2

what is the equation to work out solubility?

Answer 2

solubility (g per 100g of solvent) = mass of solid (g)/mass of water removed (g) x100