Coaching Centre
Mixtures review
A summary of the whole Mixtures chapter, key words, and a mixed test covering pure substances, solutions, colloids and suspensions, solubility, separation methods, chromatography and water treatment.
Use this page to check the whole chapter. Read the summary, make sure you can explain every key word, then do the test without looking back.
Chapter summary
| Topic | What you need to know |
|---|---|
| 5A Pure substances and mixtures | Pure substance: one kind of particle, fixed melting and boiling points. Elements (one kind of atom) and compounds (atoms chemically joined in a fixed ratio). Mixtures: not joined, any proportions, separated physically. Alloys and carats. |
| 5B Solutions, colloids and suspensions | Solution: transparent, doesn't settle, passes through filters. Colloid: cloudy, scatters a beam (Tyndall effect), never settles. Suspension: cloudy, settles, caught by filters. Emulsions and emulsifiers. |
| 5C Solutions and solubility | Solute + solvent → solution. Concentrated vs dilute; saturated. Solubility = max grams per 100 g water. Most solids more soluble when hot; gases less. Cooling a hot saturated solution forms crystals. |
| 5D Separating by size, density and magnetism | Choose a method using the property that differs. Sieving and filtering (residue and filtrate), decanting, sedimentation, flotation, centrifuging, magnets, electrostatics. |
| 5E Evaporation, crystallisation and distillation | Evaporation keeps the solute; crystallisation makes pure crystals slowly; distillation boils and condenses the solvent to keep it too. Liquids separated by boiling point. |
| 5F Chromatography | Dyes move at different speeds up the paper. Pencil start line above solvent. One spot = pure. Rf = distance moved by substance ÷ distance moved by solvent. |
| 5G Separation in the real world | Water treatment: screens, coagulation, sedimentation, filtration, disinfection, fluoride. Desalination by reverse osmosis. Sewage, blood, dialysis, froth flotation, oil spills, recycling. |
Key words
alloy · centrifuge · chromatography · coagulation · colloid · compound · concentrated · condenser · crystallisation · decanting · desalination · dilute · distillate · distillation · element · emulsifier · emulsion · evaporation · filtrate · filtration · insoluble · membrane · mixture · pure substance · residue · reverse osmosis · Rf value · saturated · sedimentation · soluble · solubility · solute · solution · solvent · solvent front · suspension · Tyndall effect
Test yourself
Which is a pure substance?
Distilled water contains only water molecules.
Paint doesn't settle, but a torch beam is visible through it when it's thinned. Paint is a
Scatters light but never settles.
The best way to get pure water from inky water is
Distillation collects the water and leaves the ink behind.
A spot moves 3.6 cm and the solvent front moves 9.0 cm. Rf =
3.6 ÷ 9.0 = 0.4.
Which property does a centrifuge use?
Denser parts are pushed to the bottom of the tube.
Solubility of a solid usually
Most solids dissolve more in hot water (salt is an exception that barely changes).
Which stage of water treatment does NOT separate anything?
Chlorine kills microbes; it doesn't remove them.
In filtering muddy water, the clear liquid that passes through is the
Filtrate passes through; residue stays.
Which method would you use?
Label the distillation apparatus.
A mixture of metals is an . The substance that dissolves is the . A solution that can't dissolve any more solute is . In distillation, vapour is cooled in the . Removing salt from sea water is called .
A student is given a mixture of sand, salt and iron filings. Describe how they could obtain each substance separately, naming the equipment and explaining the property each step uses.
First, wrap a magnet in a plastic bag and stir it through the dry mixture. The iron filings are magnetic, so they stick to the bag and can be pulled off. Next, put the sand and salt in a beaker, add water and stir: the salt is soluble and dissolves, but the sand is insoluble. Pour the mixture through filter paper in a funnel. The sand is too big to pass through and stays as the residue, which can be dried. The salt water passes through as the filtrate. Finally, heat the filtrate in an evaporating dish over a Bunsen burner. Water has a much lower boiling point than salt, so it evaporates and leaves salt crystals behind.
Explain why a solution can't be separated by filtering, but a suspension can.
In a solution, the solute is broken up into individual particles that are far smaller than the holes in filter paper, so they pass straight through with the solvent. In a suspension, the particles are clumps big enough to be seen, and larger than the holes in the paper, so they are trapped as a residue. Filtering separates by particle size, and only a suspension has particles big enough to be caught.