- Define and explain Separating by Sieving in your own words
- Use key terms such as sieve accurately
- Apply what you have learned to new examples and questions
- Avoid the common mistakes learners make with this topic
This lesson focuses on Separating by Sieving: use a sieve to separate solids of different sizes, like flour from lumps.
Use a sieve to separate solids of different sizes, like flour from lumps.
Key ideas
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.
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.
Key term — sieve: A mesh that lets small pieces through but holds back bigger ones, used to separate solids by size.
Which method would separate pebbles from sand: sieving, filtering or evaporating?
Sieving — the sand falls through the holes but the pebbles are too big.
Answer: Sieving — the sand falls through the holes but the pebbles are too big.
- Thinking sieving works for liquids A sieve separates solids by size — small pieces fall through the holes. It cannot separate two liquids, and it cannot separate a dissolved solid from a liquid.
- 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
The salt is dissolved into pieces far too small to be caught — everything passes through the holes.
Pour the mixture through filter paper: the sand is trapped and the water passes through.
Yes. The fruits are mixed but not joined, and you could pick them apart again.
No, it has dissolved. Evaporate the water and the sugar is left behind.
Quick check
Which of these best defines "sieve"?
After filtering muddy water, the water still tastes slightly salty. What does this tell you, and what would you do next?
- Separating by Sieving: use a sieve to separate solids of different sizes, like flour from lumps.
- 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.
- mixture: Two or more materials mixed together that are not joined chemically and can be separated again, such as sand and water.
- Watch out for: thinking sieving works for liquids