Mixtures, Solutions and Separation: Year 7 Study Guide
Most of what we use is a mixture. Chemists separate mixtures using differences in their properties.
The particle model says that all matter is made of tiny particles. In solids they are tightly packed and vibrate; in liquids they are close but move past each other; in gases they are far apart and move freely. Heating makes particles move faster.
A pure substance has only one kind of particle. A mixture has two or more substances mixed but not chemically joined, so they keep their own properties and can be separated physically. In a solution, a solute dissolves in a solvent (salt in water). Solubility is how much solute dissolves; it usually increases with temperature.
Separation methods
| Method | Separates | Based on | Example |
|---|---|---|---|
| Filtration | insoluble solid from liquid | particle size | sand from water |
| Evaporation | dissolved solid from solvent | boiling point | salt from sea water |
| Distillation | liquids with different boiling points | boiling point | pure water, ethanol |
| Chromatography | dissolved coloured substances | solubility and attraction to paper | ink colours |
| Magnetism | magnetic from non-magnetic | magnetic property | iron filings from sand |
| Decanting | liquid from settled solid | density | muddy water |
Dissolving and solubility
Stirring, heating and crushing the solid make it dissolve faster. A solution is saturated when no more solute dissolves at that temperature. Gases are more soluble in cold water, which is why warm drinks go flat faster. Test fairly: change one variable (temperature), keep volume and stirring the same, and measure the time to dissolve.
What will happen?
Keep the others fixed.
Record the data.
Does the evidence match the prediction?
Separating in the real world
Water treatment uses filtering and settling. Desalination removes salt from sea water by distillation or membranes. Recycling plants separate metals with magnets. Always wear safety glasses, avoid tasting any chemical and ask an adult before heating things.
Worked example and common misconceptions
Example: To separate sand, salt and iron filings: use a magnet, add water and filter, then evaporate the filtrate. Common misconceptions: thinking dissolved sugar has gone, that solutions are always clear and colourless (copper sulfate is blue) and that filtering can remove dissolved salt. Choose the method by comparing properties.
Check your understanding: model answers
1. Evaporate the water. 2. The substance that dissolves the solute, such as water. 3. Chromatography.
✨ Key Takeaways
- Matter is made of particles.
- Mixtures can be separated physically.
- Solubility depends on temperature.
- Choose the method by the differing property.
💬 Questions for Discussion & Reflection
- How would you separate salt from sea water?
- What is a solvent?
- Which method separates ink colours?
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