Solute, solvent, solution and the types of solutions
A solution is a homogeneous mixture of a solute in a solvent. Solutions are grouped by physical state, by solvent, and by how much solute they hold.
Solute, solvent and solution
Stir a spoon of sugar into a glass of water. The sugar disappears and every sip tastes equally sweet. The mixture is a solution: it is homogeneous, which means the same all through. The sugar, present in the smaller amount, is the solute. The water, present in the larger amount, is the solvent. Solution = solute + solvent. The solute particles are too small to see, do not settle down and pass through filter paper.
Types by physical state
| Solute | Solvent | Example |
|---|---|---|
| Solid | Solid | Alloys such as brass (zinc in copper) |
| Solid | Liquid | Sugar or salt in water |
| Solid | Gas | Iodine vapour in air |
| Liquid | Solid | Mercury in sodium (sodium amalgam) |
| Liquid | Liquid | Ethanol in water |
| Liquid | Gas | Water vapour in air |
| Gas | Solid | Hydrogen in palladium |
| Gas | Liquid | Carbon dioxide in water (soda water) |
| Gas | Gas | Air (oxygen and other gases in nitrogen) |
Types by solvent
Types by amount of solute (at a given temperature)
| Type | Meaning | Add one more crystal and... |
|---|---|---|
| Unsaturated | Can still dissolve more solute | It dissolves |
| Saturated | Cannot dissolve any more solute at that temperature | It stays undissolved at the bottom |
| Supersaturated | Holds more solute than a saturated solution can at that temperature; it is unstable | Extra solute suddenly crystallises out |
Activity: making the three kinds of solution
- 1Take about 100 mL of water in a beaker at room temperature.
- 2Add copper sulphate one spoon at a time and stir. While it keeps dissolving, the solution is unsaturated.
- 3Keep adding until some crystals stay at the bottom even after stirring. The solution is now saturated.
- 4Warm the beaker gently and add a little more copper sulphate until it dissolves. Filter the warm solution and let it cool slowly without shaking. It now holds more solute than a saturated solution at room temperature: it is supersaturated.
- 5Drop in one small crystal. Observe: many crystals separate out, showing the solution held extra solute.
Nimbu pani with sugar and salt is a solution: water is the solvent, and sugar, salt and lemon juice are solutes. Soda water is a gas in a liquid, and the air we breathe is a gas in a gas.
1 marks: “A solution in which water is the solvent is called ______.” An aqueous solution.
2 marks: “A solution has only one solute and one solvent. What is it called? Give one example.” A binary solution, which has two components, e.g. common salt in water.
4 marks: “Distinguish between unsaturated, saturated and supersaturated solutions, with an example of each.” Meaning of each at a given temperature, what happens when one more crystal is added, and one example: e.g. 10 g, 36 g and more than 36 g of salt in 100 g water at 25 °C.
Solute is Small, solVent is Vast. Unsaturated takes more, saturated takes no more, supersaturated throws some out.