What it does
When you stir sugar into tea it vanishes: it dissolves. The sugar is the solute, the water the solvent and the sweet tea a solution. But water cannot take an endless amount. Keep adding and a point comes when no more dissolves and the extra just sits at the bottom: the solution is saturated. How much it takes before that happens is the solubility, written as grams of solute in 100 g of water, and it depends on the temperature.
This lab gives you a beaker of water, a thermometer and three solids: table salt, sugar and potassium nitrate (KNO₃). Add spoons and watch the colour deepen until crystals start to pile up. The solubility curve below shows your beaker as a dot: under the line there is room for more, on the line it is saturated. Change the temperature and the dot and the crystals move with it. A second view, A gas, shows the opposite rule for gases: warm water holds less oxygen and carbon dioxide, which is why fish struggle in warm ponds and warm drinks go flat.
It fits Class 8 Science (solutes, solvents and solutions; saturated and unsaturated solutions; the effect of temperature), Class 9 (concentration of a solution as mass percent, crystallisation) and Class 12 Chemistry (solubility of solids and gases, molality). For what happens to the particles themselves, see states of matter; for water moving through a membrane into a stronger solution, try the osmosis lab; and for how temperature changes when a solid melts, the heating curve.
How to use it
- Choose a Level. Class 8 shows grams and saturation. Class 9 to 12 adds the mass percent and the molality of the solution.
- Under A solid, pick Salt, Sugar or KNO₃, and how much water is in the beaker (50, 100 or 200 g).
- Set the temperature with the slider or type it (0 to 100 °C).
- Press Add 1 spoon (5 g) or Add 5 spoons, or type the grams added. Empty starts again.
- Read the big line: unsaturated (with how much more will dissolve), just saturated, or saturated (with how much is left at the bottom).
- Below the curve, a line works out how many grams of crystals come out if a saturated beaker is cooled by 40 °C.
- Switch to A gas and move the water temperature (0 to 40 °C) to see oxygen for fish and carbon dioxide in a drink.
Worked example
The page opens with 100 g of water at 20 °C. Pick Salt and press Add 5 spoons once (25 g): it all dissolves, with room for 11.4 g more, because salt’s solubility at 20 °C is about 36.4 g per 100 g of water. Press Add 1 spoon twice more (35 g): still unsaturated. One more spoon makes 40 g, and the page says Saturated: 3.6 g will not dissolve. On the Class 9 to 12 level the mass percent is 36.4 ÷ (36.4 + 100) × 100 = 26.7%.
Now try KNO₃ at 60 °C: about 110 g dissolves in 100 g of water. Cool it to 20 °C, where only about 31 g can stay dissolved, and about 78 g of crystals come out. Salt’s flat curve gives back hardly anything, which is why salt is made by evaporating sea water rather than by cooling it.
Check yourself
Five fresh questions: grams that dissolve in a different amount of water, grams left at the bottom, crystals on cooling, mass percent, and a Class 12 molality question. Type a number, press Check, or show the worked answer. Nothing is saved.
Tips
- Solubility is always “per 100 g of water”. Double the water and you can dissolve double the solid, but the solubility stays the same.
- For most solids, solubility rises with temperature, but by very different amounts: compare the three curves.
- Gases are the other way round. Warm water has more energetic particles, and gas escapes more easily.
- Stirring and crushing make a solid dissolve faster, but they do not change how much can dissolve.
FAQ
Are these exact values? No. The curves are smooth rounded fits that stay within a few percent of common textbook-style values. A real experiment depends on purity and how long you stir.
Can a solution hold more than its solubility? Carefully cooled solutions can briefly be supersaturated, then crystallise all at once when disturbed. This lab leaves that out.
Is this from the NCERT book? It follows the same topics with fibub’s own pictures and examples. fibub is not part of NCERT.
Where the numbers come from
- Solubility (grams of solute that saturate 100 g of water), saturation, crystallisation on cooling, mass percent and molality, and the fall of gas solubility with temperature are standard school chemistry. Wording, pictures and examples are fibub's own.
- The solubility curves are smooth fits written for this page, rounded to within about 5% of common general values: salt about 36 g at 20 °C and 39 g at 100 °C, sugar about 204 g at 20 °C and 487 g at 100 °C, potassium nitrate about 32 g at 20 °C and 246 g at 100 °C. Oxygen in air-saturated water about 14.6 mg/L at 0 °C and 9.1 mg/L at 20 °C; carbon dioxide under 1 atm about 3.3 g/L at 0 °C and 1.7 g/L at 20 °C. Molar masses from IUPAC standard atomic weights.
- Checked in tests against hand-worked examples and the rounded general values above.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.