How much can dissolve?
Solubility and saturated solutions.
Sugar in tea
You keep adding spoons of sugar to a cup of tea and stirring.
What will happen after many spoons?
What this lesson covers
The idea
Solubility is the maximum amount of solute that dissolves in a fixed quantity of solvent (100 mL or 100 g) at a given temperature; a solution that cannot dissolve any more solute at that temperature is saturated.
Sugar in tea
You keep adding spoons of sugar to a cup of tea and stirring.
What will happen after many spoons?
- Some sugar stops dissolving and stays at the bottom
- All the sugar keeps dissolving, whatever the amount
- The tea turns into sugar crystals at once
Add salt, a little at a time
Add salt to 100 g of water. Watch for the point where it stops dissolving.
Solubility and saturation
The maximum amount of solute that dissolves in a fixed quantity of solvent (100 mL or 100 g) at a given temperature is its solubility. A solution that cannot dissolve any more solute at that temperature is a saturated solution.
We always mention the temperature, because solubility changes with temperature. Solubility is an important property used to separate substances from mixtures.
The 36 g here is the solubility of common salt in water at about 20 °C, a well-known value used as an example.
Notes
Solubility is the maximum amount of solute that dissolves in a fixed quantity of solvent at a given temperature. A solution that cannot dissolve any more is saturated.
Check yourself
What is the solubility of a solute?
A solution that cannot dissolve any more solute at that temperature is…
At 20 °C, 100 g of water dissolves at most 36 g of salt. You add 50 g. How many grams stay undissolved?
Answer: 14 g
50 g − 36 g = 14 g stays undissolved.
Why do we mention the temperature with a solubility?
- The maximum amount that dissolves in a fixed quantity of solvent at a given temperature — correct. Yes.
- The amount of solvent in the beaker. That is not the solute’s solubility.
- How fast it dissolves. Solubility is about how much, not how fast.
- dilute. A dilute solution can still dissolve more.
- saturated — correct. Yes.
- homogeneous only. Every solution is homogeneous, but this one is saturated.
- Because water is always at 20 °C. The temperature can be different.
- Because salt is a gas. Salt is a solid.
- Solubility changes when the temperature changes — correct. Yes.