KS3 · Chemistry
Mixtures and solutions
Stir sugar into water and it vanishes. Stir in sand and you can still see every grain. So what makes sugar different — and where has it actually gone?
Chemistry · Solutions
Solute, solvent or solution?
Here are three real solutions, split into their parts. Pick each one up and put it in the job it does.
Still to sort
Solute (0)
The substance that dissolves.
Where the line is: It's what goes INTO the liquid — never the liquid itself.
Solvent (0)
The liquid it dissolves into.
Where the line is: It's just the liquid part — not the finished mixture.
Solution (0)
Solute and solvent combined.
Where the line is: It's never one ingredient on its own — it's what you get when the two combine.
Three similar-sounding words, three different jobs. Once you can give every ingredient its job, the words stop blurring together.
Predict, then check
Iodine won't dissolve in water — yet you've just sorted it as the solute in a solution with cyclohexane. Now flip it round with sugar.
Sugar dissolves easily in water. What happens if you stir sugar into cyclohexane instead?
WHAT YOU'VE LEARNED
A quick recap of today's lesson.
Why sugar vanishes into water, why sand doesn't — and where the sugar actually goes.
What you need to know
- Which part of a solution is the solute, which is the solvent, and which is the solution itself
- What soluble and insoluble mean — and why you always need to say which liquid
- Why a dissolved substance still has mass, and how to use that to work out a missing mass in grams
The big picture
A solution is a mixture made when a substance dissolves in a liquid so well that it can no longer be seen. The substance that dissolves is the solute, the liquid it dissolves into is the solvent, and together they make the solution. A solute can be a solid, a liquid or a gas, and whether it dissolves depends on the solvent. Because the particles are all still there, mass is conserved: mass of solute + mass of solvent = mass of solution.
Key points
Worked example
Problem
Jess dissolved 15 g of sugar in some water. Her sugar solution weighs 135 g. How much water did she use?
⚠ Watch out
Swapping solute and solvent. The solute is the substance that dissolves; the solvent is the liquid it dissolves into. If you're unsure, ask "which one dissolved?" — that one is the solute.
Memory hook
Gone from sight, not from the scales. The solUTE is the one that dissolves, the solVENT is the liquid it goes into, and the solUTION is what you end up with — and on the balance, the two you start with add up to the one you finish with.
Check yourself
10 g of sugar dissolves completely in 90 g of water. Name the solute and the solvent, then work out the mass of the solution.
Flashcards
(12)What is a solute?
What is a solvent?
What is a solution?
What does it mean when a solid has dissolved?
Soluble or insoluble — what's the difference? Give an example of each.
Is every mixture a solution?
What is the most common solvent?
Iodine and sugar: which liquid does each dissolve in?
Can a solute be a gas?
What unit is mass measured in, and with what?
Why is mass conserved when a solution forms?
Write the word equation linking the masses when a solution is made.
Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.
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Keep me postedMore KS3 Chemistry topics
- Acids, bases and alkalis
- Boiling and condensing
- Changes of state: energy and evaporation
- Characteristics of chemical reactions
- Chemical formulae and symbols
- Chromatography
- Combustion
- Composition of the atmosphere
- Compounds and their formation
- Conservation of mass and balanced equations
- Displacement of metals
- Dissolving
How this lesson was checked. This KS3 Chemistrylesson was published through Lightbulb Learning's human-designed editorial process — the educational standards, accuracy rules and publication checks it must pass were authored and approved by Philip Halpin. It passed subject-specific assessment, automated educational checks and technical publication verification before going live (publication checks completed 29 September 2026). Published pages are monitored, human spot-checking is ongoing across the lesson library, and anything found wrong is corrected or withdrawn. How our lessons are made and checked. Spotted a mistake? Email hello@lightbulblearning.co and we'll review it.