Solution, colloid or suspension?
Shine a torch through twelve mixtures, from salt water and vinegar to milk, fog and muddy water, filter them, and sort them by the size of their particles.
Core concept
A solution's particles are smaller than 1 nm and let light through unseen; a colloid's (1 to 1000 nm) scatter a beam of light (the Tyndall effect) but pass through filter paper; a suspension's are bigger, settle and are filtered out
Topic: Matter: mixtures
A mixture: Two or more substances mixed together, which can be separated again. All key words can be a solution: A mixture where one substance has dissolved completely in a liquid, like salt water. All key words, a colloid or a suspension, and the size of its particle: A tiny piece that matter is made of, far too small to see. All key words decides which. In a solution, such as salt water, the particles are smaller than 1 nanometre: the liquid is clear, a beam of light passes through unseen, and nothing settles or is caught by filtration: Separating solid bits from a liquid by pouring it through filter paper or cloth. All key words paper. In a colloid, such as milk, the particles are about 1 to 1000 nm: too small to settle or be filtered, but big enough to scatter light, so a torch beam shows up as a bright path. This is the Tyndall effect, the same one that makes sunbeams visible in a dusty room or headlights visible in fog. In a suspension, such as muddy water, the particles are bigger than 1000 nm: it is cloudy, the particles settle when left to stand, and filter paper stops them.
What you will learn
- Explain the Tyndall effect.
- Tell solutions, colloids and suspensions apart with a torch beam and filter paper.
- Relate each kind of mixture to the size of its particles.
Before you start
- Know what a mixture and a solution are.
Materials
- Salt, sugar, milk, soap, starch, chalk powder, sand, mud and wheat flour
- Clear glasses or beakers
Equipment
- A torch or a laser pointer
- Filter paper and a funnel
Procedure
- Pick a mixture card and shine a torch through it from the side.
- Pour it through filter paper and see what is left.
- Do this for at least eight mixtures, then sort them all.