Science
What are mixtures and solutions?
Quick answer
A mixture is two or more substances mixed but not joined chemically. A solution is a mixture where one substance, like salt, dissolves completely in a liquid, like water.
In one sentence
A mixture is a combination of substances that are not chemically joined, and a solution is a special mixture in which something dissolves in a liquid.
Explained
Mix sand and sugar in a bowl and you have a mixture. You can still see both substances, and each keeps its own properties. Because they are not chemically joined, a mixture can be separated again; see separating mixtures. Salad, sea water, air and muddy puddles are all mixtures. Air is a mixture of gases.
Now stir a spoonful of sugar into water. The sugar seems to disappear. This is a solution. The sugar has dissolved. Its tiny particles have spread out evenly between the water particles, so the liquid looks clear.
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In a solution:
- The substance that dissolves is the solute (sugar).
- The liquid that it dissolves into is the solvent (water).
- Together they make the solution (sugar water).
A substance that can dissolve is soluble. Salt, sugar and coffee granules are soluble in water. One that cannot dissolve is insoluble, like sand, flour or chalk. If you stir sand into water, it spreads for a moment, but soon sinks again. That kind of cloudy mixture is not a solution.
Dissolving is not the same as melting. The sugar is still there, and you can taste it. The mass stays the same: if you dissolve 10 grams of salt in 100 grams of water, you will have 110 grams of salt water. If you let the water evaporate, the salt is left behind.
Warm water usually dissolves things faster and lets you dissolve more. But there is a limit. When no more will dissolve, the solution is saturated. Learn about the three states of matter in solids, liquids and gases, and the kinds of materials we use.
Examples
| Mixture | Solution? | Why |
|---|---|---|
| Salt in water | yes | salt dissolves |
| Sugar in tea | yes | sugar dissolves |
| Sand in water | no | sand is insoluble |
| Oil and water | no | they do not mix |
| Flour in water | no | it spreads out but settles |
Common mistakes
- "The sugar vanished." It is still there, in tiny particles.
- "Clear means pure." Salt water is clear, but it is a mixture.
- "Dissolving means melting." Dissolving needs a liquid.
Quick quiz
Mixtures and solutions
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Question 1 of 4
What is a solution?
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Related topics
Materials
Materials are what objects are made from, such as wood, metal, plastic and glass. Each has properties, like being hard, bendy, waterproof or see-through, that suit it to some jobs.
Separating mixtures
Mixtures can be separated by using the different properties of their parts. Common methods are sieving, filtering, evaporation, magnets and chromatography.
Evaporation
Evaporation is when a liquid slowly turns into a gas from its surface, like a puddle drying in the sun. It happens faster when it is warm, windy or the liquid is spread out.
Elements, compounds and mixtures
An element has only one kind of atom. A compound is two or more elements chemically joined in a fixed ratio, like H₂O. A mixture is substances mixed but not joined, so they can be separated.
Physical and chemical changes
A physical change alters how a substance looks or its state but makes nothing new, like ice melting. A chemical change makes new substances, like wood burning to ash and smoke.
Adaptation
An adaptation is a feature or behaviour that helps a living thing survive where it lives. A polar bear's thick fur and a cactus's spines are adaptations.