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Solubility and solubility curves, definition of a solvent and a solute

Answer Text:
Solubility and solubility curves
Solubility:
- Is the maximum number of grams of a solid which will dissolve in 100g of solvent (usually water) at a particular temperature
- A solution is made up of two parts: - a solute and a solvent.
Solute
- The solid part of a solution usually dispersed in the solvent e.g. a salt.
Solvent
- The liquid part of the solution into which the solute is dissolved.
Experiment: to determine the solubility of potassium nitrate at #20^oC#.
(i). Materials
- Beakers, evaporating dish, measuring cylinder, burner, scales, thermometer, distilled water and potassium nitrate
(iii). Procedure
- About #50cm^3# of distilled water is placed in a beaker
- Potassium nitrate is added to it a little at a time stirring continuously.
- The nitrate is added until no more will dissolve and there is an excess undissolved salt present.
This is the saturated solution of #KNO_3# at the temperature.
Note:
Saturated solution: solution that cannot dissolve any more of the solid/ solute at a particular temperature
- The solution is allowed to settle and it is temperature recorded.
- About 25#cm^3# of clear solution is poured in a previously weight evaporating dish.
- The mass of the dish and solution is recorded.
- The dish is then heated in a water bath (to avoid spurting) till the solution is concentrated.
- The concentrated solution is allowed to cool and the dish weighted with its
contents.

Calculating:
Mass of salt dissolved =(73.8 – 65.3)g = 8.5g;
Mass of water (solvent) =(35.4 – 8.5)g = 26.9g
Thus:
If 26.9g of water dissolves 8.5g of #KNO_3# at #20^0C#;
Then 100g of water will
have ? =# frac{100 times 8.5}{26.9}# = 31.6g of salt;
Therefore the solubility of
#KNO_3# at #20^oC# = 31.6g per 100g of water