Solutions and Separating Mixtures
Not everything is a pure substance. Most of what you meet each day, from ocean water to the air, is a mixture, and mixtures can be pulled apart again by simple physical methods. Knowing how solutions form and how to separate a mixture is practical chemistry that shows up on nearly every science test.
This lesson explains solutions and walks through the common ways to separate mixtures.
A mixture is a physical blend of substances that are not chemically combined, so it can be separated by physical means. A solution is a mixture in which one substance dissolves evenly into another, like salt in water. Separation methods, such as filtration, evaporation, and distillation, take advantage of differences in properties like particle size and boiling point.
What is a solution?
A solution is a special kind of mixture where one substance completely dissolves into another and spreads out evenly. The substance being dissolved is the solute, and the substance doing the dissolving is the solvent. In salt water, salt is the solute and water is the solvent. Because the mixing is even, every sip of salt water tastes equally salty.
Solutions are still mixtures, not compounds. The salt and water are not chemically bonded, which is exactly why you can get the salt back by removing the water.
How do you separate a mixture?
Because the parts of a mixture keep their own properties, you can separate them by exploiting a difference. The method you choose depends on which property differs the most.
Filtration separates an insoluble solid from a liquid by passing the mixture through a filter that traps the solid, like straining pasta. Evaporation recovers a dissolved solid by letting the liquid turn to vapor and leaving the solid behind, which is how salt is harvested from seawater. Distillation separates liquids by boiling point: the mixture is heated, the lower-boiling liquid evaporates first, and its vapor is cooled back into a pure liquid. A magnet can even separate iron filings from sand.
| Method | Separates by | Example |
|---|---|---|
| Filtration | Particle size (solid vs liquid) | Sand from water |
| Evaporation | One part becomes a gas | Salt from salt water |
| Distillation | Boiling point | Pure water from salt water |
Solubility: why some things dissolve and others do not
Solubility is how much of a solute can dissolve in a solvent. Stirring, heating, and breaking a solid into smaller pieces all help it dissolve faster. But there is a limit: once a solution holds all the solute it can at a given temperature, it is saturated, and no more will dissolve. Warmer water usually dissolves more solid solute, which is why sugar mixes more easily into hot tea than iced tea.
Watch: A Short Video Lesson
iitutor walks through this skill clearly in a few minutes. It is a helpful companion to the reading above:
A routine for mixture questions
- Confirm it is a mixture: the parts keep their own properties and are not chemically bonded.
- For a solution, name the solute (dissolved) and the solvent (doing the dissolving).
- To separate, find the property that differs most: size, boiling point, or magnetism.
- Match the method: filtration for solids in liquid, evaporation for a dissolved solid, distillation for liquids.
- Remember separation is physical, so no new substances form.
Practice questions
- In salt water, which part is the solute and which is the solvent?
- Which method would separate sand from water?
- Which method recovers pure water from salt water?
- Name two things that make a solid dissolve faster.
- What does it mean for a solution to be saturated?
- True or false: separating a mixture creates new substances.
Answers:
- Salt is the solute; water is the solvent.
- Filtration.
- Distillation.
- Any two of: stirring, heating, or crushing the solid into smaller pieces.
- It holds all the solute it can at that temperature, so no more will dissolve.
- False. Separation is a physical process; no new substances form.
Where this fits
Solutions and separation build on the idea of elements, compounds, and mixtures and connect to the physical changes that make separation possible. Because dissolving does not form new substances, it stays firmly in the world of physical change. Find every topic on the ASVAB General Science Learning Hub.
Recommended Prep Books
These study guides and practice books help you keep building momentum as you prepare:
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