Separating Mixtures

Science · Matter & Materials · ages 9-10

Name ______________________ Date ____________

Sand is mixed into water and doesn't dissolve. Which method separates the sand from the water?
- Sieving
- Filtering
- Evaporating
You have a mixture of pebbles and sand, both dry. Which method separates them?
- Sieving
- Filtering
- Evaporating
Evaporating is the best way to get salt back from salty water.
Circle one: True False
Why doesn't a filter catch the salt that's dissolved in water?
- The salt has broken apart into pieces too tiny for the filter to trap
- The filter paper dissolves in the water
- Salty water moves too fast through the filter
You have a mixture of sand and salty water. What's the plan to separate all the parts?
- Evaporate the water first, then filter
- Sieve the water to remove the salt
- Filter out the sand, then evaporate the water
A mixture has big gravel, fine sand, and salty water all together. Which order separates everything?
- Filter everything first, then sieve the liquid
- Sieve the gravel out, filter the sand from the water, then evaporate the water
- Evaporate first, then sieve, then filter
Zara has iron filings, sand, and salty water mixed together. A magnet already pulled out the iron. What are her next two steps?
- Filter out the sand, then evaporate the salty water
- Sieve out the sand, then filter the water
- Evaporate the sand, then filter the salt
Tom sieves his sand-and-salty-water mixture, hoping to catch the salt. What went wrong with his plan?
- Sieves only work on liquids, not solids
- He should have evaporated the sand instead
- Salt is dissolved, so it's too small for a sieve to catch

Answer key

For grown-ups. Fold this page away before handing over the rest.

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Filtering · Filtering traps solid pieces too small for a sieve but still undissolved, while the liquid passes through the paper.
Sieving · Sieving works when solid pieces are different sizes. The holes let small pieces through and keep big ones on top.
True · Dissolved salt can't be trapped by a sieve or filter, so heating away the water is the way to get it back.
The salt has broken apart into pieces too tiny for the filter to trap · Once salt dissolves, it breaks apart so small that it slips right through filter paper along with the water.
Filter out the sand, then evaporate the water · Filtering removes the solid sand first. Only then can you evaporate the remaining salty water to get the salt.
Sieve the gravel out, filter the sand from the water, then evaporate the water · Start with the biggest pieces using a sieve, then the smaller solid pieces using a filter, then finish with the dissolved part.
Filter out the sand, then evaporate the salty water · Filtering catches the sand because it doesn't dissolve, and evaporating the leftover salty water brings back the dissolved salt.
Salt is dissolved, so it's too small for a sieve to catch · Once salt dissolves it isn't a separate solid piece anymore, so no sieve or filter can catch it. Only evaporation works.