Science

Solute, Solvent and Solution: Which Word Is Which

The solute dissolves, the solvent does the dissolving, and the mixture is a solution. Dissolving hides a substance but destroys nothing: the mass still adds up.

Solute and solvent

A solute is a substance that dissolves in a liquid, the solvent is the liquid that dissolves it, and the mixture they form together is a solution.

Where students meet it: Grade 5 science, in the first unit on mixtures and how to separate them, and again in Grade 8 where concentration is worked out in grams per cubic decimetre.

The short answer
The solute is the substance that dissolves, the solvent is the liquid it dissolves into, and together they form a solution. In salty water, salt is the solute and water is the solvent. Dissolving hides the solute but destroys nothing: the mass of the solution equals the two masses added together.

An example

10 g of salt + 100 g of water = 110 g of salt solution

This is the question examiners actually ask, and the wrong answer is 100 g. Put a beaker of water on a balance, note the reading, stir in a weighed spoonful of salt and read the balance again. The total has gone up by exactly the mass of the salt. Nothing has been destroyed — the salt particles have separated and slotted into the spaces between the water particles, which is why they can no longer be seen.

Three words, one mixture

The three terms describe three different things in the same beaker, and the quickest way to keep them apart is to ask which one was solid before you started. That one is the solute. The liquid it went into is the solvent. The clear mixture you are now looking at is the solution.

A substance that dissolves in a given solvent is described as soluble in it; one that does not is insoluble. Both words need the solvent naming to mean anything. Chalk is insoluble in water and wax is insoluble in water, but wax dissolves readily in white spirit, so calling a substance simply insoluble says less than it seems to.

Solute — the substance being dissolved, such as the salt, sugar or copper sulfate
Solvent — the liquid doing the dissolving, usually but not always water
Solution — the mixture that results, which is clear, may be coloured, and is the same all the way through

Dissolved is not disappeared

A solution looks like a single substance, which is where the trouble starts. The solute particles are still there, spread evenly through the solvent and far too small to see or to be caught by filter paper. Pour salt water through a filter and salt water comes out the other side. That is the test that separates a solution from a suspension: sand in water leaves the sand behind on the paper, and it settles if you leave it alone.

Because nothing has reacted, the change is a physical one and it runs backwards. Evaporate the water and the salt is left in the dish, unchanged in mass and chemically identical to the salt that went in.

Water is not the only solvent

Water gets called the universal solvent, which is a nickname rather than a fact. It dissolves an unusually wide range of substances, and it is the solvent inside every living cell, but sand, oil, wax and most plastics ignore it completely.

Other solvents fill the gaps, and each is chosen because it dissolves something water will not. Nail varnish remover is usually propanone. Ethanol is the solvent in many inks, perfumes and medicines. White spirit thins gloss paint. When a label says a stain needs a particular cleaner, this is the reason.

Common questions

Is salt water a mixture or a solution?

Both, because a solution is a kind of mixture. The salt and the water are not chemically joined, and each keeps its own properties, which is what makes it a mixture. It is called a solution specifically because one substance has dissolved in the other and spread evenly through it.

Why does the mass not change when sugar dissolves?

Because no particles are created or destroyed — they are only separated and mixed in. Every sugar particle that goes into the water is still in the beaker afterwards. If a balance appears to show a loss, something has escaped, usually water vapour from an open beaker rather than the solute.

What is a saturated solution?

One that has dissolved as much solute as it can hold at that temperature, so any extra sits undissolved at the bottom. Heating the solvent usually raises the limit for a solid solute, which is why more sugar dissolves in hot tea, and why crystals reappear as a hot saturated solution cools.

How do you get the solute and the solvent back separately?

To recover the solute, evaporate the solvent away and leave the solid behind, or cool a hot saturated solution to grow crystals. To recover the solvent instead, use distillation: boil the solution, then cool the vapour back to a liquid in a condenser. The solute stays in the flask.

Last updated August 21, 2026