Mixtures & Solutions

A mixture is two or more things combined but not chemically joined, and a solution is a special mixture where one substance dissolves completely and evenly into another.

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Definition

A mixture is made when two or more materials are put together but each material keeps its own properties and can be separated again. A solution is a type of mixture where one substance (the solute) dissolves so completely into another substance (the solvent) that you cannot see the individual parts anymore — the result looks the same throughout.

Remember the rule

Mixture = parts stay themselves + can be separated. Solution = one part disappears into the other + looks the same everywhere.

Key words

Mixture: Two or more substances combined together where each part keeps its own properties and can be separated back out.
Solution: A special mixture where one substance dissolves completely into another so everything looks the same throughout.
Solute: The substance that gets dissolved in a solution — for example, the salt in saltwater.
Solvent: The substance that does the dissolving — for example, the water in saltwater.
Dissolve: When a solid (or gas) breaks apart into tiny, invisible pieces and mixes evenly into a liquid.
Heterogeneous: A mixture that looks different in different spots — you can see the separate parts, like trail mix.
Homogeneous: A mixture that looks exactly the same throughout — like lemonade or saltwater.
Solubility: How much of a substance can dissolve in a liquid — sugar has high solubility in water because a lot of it dissolves.

Worked examples

You stir 1 teaspoon of salt into a cup of water. Is this a mixture or a solution?

→ It is a solution. The salt (solute) dissolves completely into the water (solvent). The water looks clear and the same throughout. You cannot see the salt anymore. · Even though you cannot see the salt, it is still there — if you let the water evaporate, the salt is left behind.

You mix together a handful of raisins, peanuts, and chocolate chips in a bowl. Is this a mixture or a solution?

→ It is a mixture — specifically a heterogeneous mixture. You can still see and pick out each ingredient. Nothing dissolved into anything else. · Because the parts are still visible and separate, this is the easiest kind of mixture to understand.

You mix sand and water in a jar and shake it. Is the sand dissolving?

→ No. The sand does not dissolve — it just floats around and then sinks to the bottom. This is a mixture but NOT a solution, because the sand does not disappear into the water. · You can separate the sand from the water by pouring it through a coffee filter.

You add 2 spoonfuls of sugar to iced tea and stir. What happens and what type of mixture forms?

→ The sugar dissolves into the tea, forming a solution. The tea tastes sweet all the way through and looks the same everywhere — that is the sign of a solution.

You mix oil and water together and shake the bottle. Is this a solution?

→ No. Oil and water do not dissolve into each other. When you stop shaking, they separate into two visible layers. This is a heterogeneous mixture, not a solution. · Oil molecules and water molecules are too different from each other to mix at the particle level.

You dissolve as much sugar as possible into hot water until no more will dissolve. What do you call this?

→ You have made a saturated solution. The water has dissolved all the sugar it possibly can. Any extra sugar you add will just sit at the bottom and not dissolve.

Common mistakes

Thinking that a solution means the solute disappears forever — it is still there, just broken into invisible particles that can be recovered (for example, by evaporation).
Calling every liquid a solution — plain water is not a solution, and oil-and-water is a mixture but not a solution.
Confusing the solute and solvent — remember: the solvent is usually the larger amount (the water), and the solute is the smaller amount being dissolved (the salt or sugar).
Thinking all mixtures can be separated the same way — sand and water can be filtered, saltwater must be evaporated, and trail mix can just be picked apart by hand.
Believing something must look cloudy or dirty to be a mixture — a clear glass of saltwater is a mixture (and a solution) even though it looks like plain water.

FAQs

Is all solutions mixtures, or are all mixtures solutions?

All solutions are mixtures, but not all mixtures are solutions. A solution is just a special kind of mixture where everything dissolves evenly. Trail mix is a mixture but definitely not a solution.

How can you tell if something dissolved or just sank to the bottom?

If it dissolved, the liquid looks clear and the same throughout, and you cannot find the solid anywhere. If it just sank, you can see the solid sitting at the bottom — that means it did not dissolve and you do not have a solution.

Does temperature affect how well something dissolves?

Yes! Hot water usually dissolves solids like sugar and salt faster and in greater amounts than cold water. That is why hot tea dissolves more sugar than iced tea does.

Can gases and solids be solvents, or is it always a liquid?

Liquids are the most common solvents, but gases can form solutions too — air is actually a solution of gases (mostly nitrogen with oxygen and other gases dissolved in it). For 5th grade, focus on liquid solvents like water.

How do you separate a solution like saltwater?

You can evaporate the water by heating it. The water turns into water vapor and leaves, but the salt stays behind in the container. This process is called evaporation and it proves the salt was really there all along.

What does it mean when we say water is the universal solvent?

It means water can dissolve more different substances than almost any other liquid. That is why water is used in so many solutions — from ocean water to the blood in your body to the drinks you consume every day.

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