- Define and explain What Is a Mixture in your own words
- Use key terms such as mixture accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
Muesli, soil and seawater are all mixtures — materials mixed together that can be separated again. Scientists have clever ways to pull mixtures apart, choosing the method that fits the materials. In this chapter you will sieve, filter and evaporate your way to clean separations.
This lesson focuses on What Is a Mixture: learn how mixtures are made of two or more materials mixed together.
Learn how mixtures are made of two or more materials mixed together.
Key ideas
Mixtures can be undone
In a mixture, the materials are jumbled together but not joined — a bowl of sand and water is still sand plus water. Because nothing new has been made, mixtures can usually be separated back into their parts. This is different from baking, where the ingredients change into something new.
Choose the method that fits
Each separation method suits a particular mixture: sieving separates solids of different sizes, filtering separates an insoluble solid from a liquid, and evaporation recovers a dissolved solid from its solution. Scientists look at the properties of the parts — size, solubility, state — and then pick the method. Using the wrong method, like trying to sieve salt water, simply does not work.
Key term — mixture: Two or more materials mixed together that are not joined chemically and can be separated again, such as sand and water.
You have muddy water (mud mixed with water). Describe how to get cleaner water and dry mud using filtering and evaporating.
Pour the muddy water through filter paper in a funnel. The mud is trapped on the paper while the water drips through — the solid and liquid are now apart. Leave the trapped mud somewhere warm to dry. The water collected in the beaker is much cleaner; evaporating some of it would leave any dissolved substances behind as well.
Answer: Filter the mixture to trap the mud on the paper, collect the water underneath, then dry the mud by leaving it somewhere warm.
- Forgetting that evaporation needs the liquid to escape Evaporation only separates a mixture if the vapour can leave. Warming salt water in a sealed jar just makes it steamy — leave it open so the water vapour escapes and the salt stays behind.
- Trying to filter a dissolved solid Filter paper traps solid lumps but dissolved salt passes straight through with the water. To get dissolved salt back, evaporate the water instead.
Practice
Yes. The fruits are mixed but not joined, and you could pick them apart again.
Pour the mixture through filter paper: the sand is trapped and the water passes through.
Sieving — the sand falls through the holes but the pebbles are too big.
No, it has dissolved. Evaporate the water and the sugar is left behind.
Quick check
Which of these best defines "mixture"?
After filtering muddy water, the water still tastes slightly salty. What does this tell you, and what would you do next?
Why can you not separate salt water with a sieve?
- What Is a Mixture: learn how mixtures are made of two or more materials mixed together.
- Mixtures can be undone: In a mixture, the materials are jumbled together but not joined — a bowl of sand and water is still sand plus water.
- filter: To pass a mixture through paper or cloth that traps the solid but lets the liquid through.
- Watch out for: forgetting that evaporation needs the liquid to escape