Separation and purification
| English | Chinese | Pinyin |
|---|---|---|
| separation techniques | 分离技术 | fēn lí jì shù |
| filtration | 过滤 | guò lǜ |
| crystallisation | 结晶 | jié jīng |
| simple distillation | 蒸馏 | zhēng liú |
| fractional distillation | 分馏 | fēn liú |
Getting pure substances
- Mixtures are everywhere, but chemists often need a pure substance.
- Several separation techniques 分离技术 do the job, each suited to a different mixture.
Separation method lab
Choose the method that matches the mixture.
Filtration is used to separate:
Filtration removes insoluble solids.
To recover a dissolved solid from its solution, you use:
Evaporate the solvent and crystallise the solid.
Filtration 过滤 and crystallisation 结晶
- Filtration separates an insoluble solid from a liquid.
- Crystallisation gets a dissolved solid back by evaporating the solvent.
Filtration separates an insoluble solid (residue) from a liquid (filtrate)
Pure water can be separated from salt water by:
Distillation boils off and condenses the water.
Fractional distillation separates liquids with different boiling points.
It is used for crude oil and alcohol-water mixtures.
Distillation
- Simple distillation 蒸馏 separates a solvent from a solution (e.g. pure water from salt water).
- Fractional distillation 分馏 separates liquids with different boiling points (e.g. crude oil, alcohol from water).
Fractional distillation adds a fractionating column, so liquids with different boiling points separate cleanly
An insoluble solid is separated from a liquid by ______.
Filtration traps the solid.
Choosing the method
- Pick the technique by what you want to separate.
- Insoluble solid → filter; dissolved solid → crystallise; liquids → distil.
Worked example. To get pure water from salt water, use simple distillation: the water boils off, is condensed and collected, leaving the salt behind. The right method depends on the mixture.
You've got it
- filtration removes an insoluble solid; crystallisation recovers a dissolved solid
- simple distillation separates a solvent; fractional distillation separates liquids by boiling point
- choose the method to match the mixture