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Science / Class 6–9 / 12 min / Medium

Solutions and Solubility: How Much Will Dissolve?

Understand that solubility is the maximum mass of a solute that dissolves in a fixed amount of solvent at a given temperature, that it usually rises with temperature, and that extra solute beyond that point stays undissolved.

Before you try

What if you cooled a full glass of sugary water? Where would the extra sugar go?

Try it out

Interactive activity

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What happened?

Move a control to see what changes and why.

Stirring works instantly and the temperature is fixed. In reality dissolving takes time, and most solids dissolve better when warm.

Try these ideas

  • Saturate potassium nitrate at 80 °C, then cool it and watch crystals appear.
  • Compare how much salt and how much sugar dissolve in the same water.
  • Double the water and see what happens to the amount that dissolves.

Why it works

Dissolving is not magic: water can only hold so much of any substance before it runs out of room. That limit is the solubility, usually quoted as grams per 100 grams of water at a stated temperature. Add exactly that much and the solution is saturated. Add more and the extra simply sits on the bottom, however hard you stir, because stirring changes how fast it dissolves and not how much can dissolve.

In this simulator you choose a solute, set the temperature, the water volume and how much you add, then watch the dissolved particles, the undissolved pile and the concentration figures. The solubility curve for your solute is drawn with your current point marked. The figures are approximate published values, interpolated between the tabulated temperatures.

Check your understanding

Question 1 of 4

A solution is saturated. What happens if you add more solute at the same temperature?

What does stirring change?

You cool a saturated hot solution of potassium nitrate. What do you see?

Which usually dissolves more in hot water than in cold?

Explain it in your own words

What changed? Why did it happen? Where might you notice this in everyday life?

What will you discover next?

Try Acids, Bases and pH: Test Virtual Liquids next.

Continue learning

For parents & teachers

  • Dissolve salt in cold and in hot water at home and compare.
  • Ask why sea water leaves salt behind when it evaporates in salt pans.
  • Grow a crystal from a saturated solution on a string over a few days.

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