Year 5 Science · Solutions and separating mixtures · Lesson 6.5

Year 5 Science: Filtering, and choosing a method

Part of the Year 5 Science solutions and separating mixtures chapter. Chapter overview · whole chapter on one page

6.5

Filtering, and choosing a method

Year 5
M4: decide how mixtures might be separated, including filtering and evaporating

Story. Mr Patel has three mixtures in the lab: sand and water, salt and water, and sand and pebbles. “Which method would you use for each one?” he asks. “Give me a reason, based on what you know about solids and liquids.”

Filtering separates a solid that does not dissolve from a liquid. The liquid passes through the filter paper, and the solid is left in the paper.

Evaporating separates a dissolved solid from its solvent. The solvent turns into vapour and leaves the solid behind.

A funnel with filter paper. Sand stays in the paper, and clear water runs into a beaker.

Mixture	Method to separate it	Why this method works
sand and water	filtering	the sand is a solid that does not dissolve, so filter paper holds it back
salt and water	evaporating	the salt dissolves, so it must be left behind when the water evaporates
sand and pebbles	sieving	the particles are different sizes, so a sieve keeps the big pieces
sugar and water	evaporating	the sugar dissolves, and the water evaporates to leave the sugar

Key ideas

Filtering separates an insoluble solid from a liquid, using filter paper.
Evaporating separates a dissolved solid from its solvent.
Sieving separates solids of different particle sizes.
Choose the method by thinking about whether the solid dissolves, and whether the particles differ in size.

Worked example 6.5.1

Which method would separate sand from water? Write the word.

Method. Think about whether the sand dissolves.

Think about the sand. Sand does not dissolve in water, so it can be held back by filter paper.
does not dissolve
Choose the method. So the method is filtering.
filtering
Write the answer.
filtering

Check. Filter paper holds back the sand, and the water runs through. ✓

Worked example 6.5.2

Which method would separate salt from water? Write the word.

Method. Think about whether the salt dissolves.

Think about the salt. Salt dissolves, so filter paper cannot separate it.
dissolves
Choose the method. So the method is evaporating.
evaporating
Write the answer.
evaporating

Check. Evaporating leaves the salt behind. ✓

Worked example 6.5.3

Which method would separate sand and pebbles? Write the word.

Method. Think about the sizes of the particles.

Think about the sizes. Sand and pebbles are different sizes.
different sizes
Choose the method. So the method is sieving.
sieving
Write the answer.
sieving

Check. The sieve holds back the pebbles. ✓

Watch out

Watch out: filtering does not separate salt from water, because the salt dissolves and passes through the filter paper with the water.

Try it (with your teacher). With your teacher, pour a little sand and water through filter paper in a funnel. Watch the water run through, and look at the paper. Then explain which method you would use to get the salt back from salt water.

Exam tip

Grown-up tip. Ask: “Does the solid dissolve? If it does not, what can you use? If it does, what happens to the water?” Let your child explain each choice.

Exercise 6E Filtering, and choosing a method

FWhich method separates a solid that does not dissolve from a liquid? Write the word.

Done

FWhich method separates a dissolved solid from its solvent? Write the word.

Done

FWhich method separates solids of different particle sizes? Write the word.

Done

FLook at the method table in section 6.5. Which method separates sugar and water? Write the word.

Done

FLook at the method table in section 6.5. Which mixture is separated by filtering? Write the words.

Done

FLook at the method table in section 6.5. How many of the four mixtures are separated by evaporating? Write the number.

Done

PSWhich method separates a mixture of sand and water? Write the word: sieving, filtering or evaporating.

Done

PSWhich method is best for getting the salt back from salt water? Write the word.

Done

PSMo says: “I can separate salt from water by filtering.” Is Mo right? Write yes or no.

Done

PSWorking scientifically. Choose a method and justify it. A mixture of sand and pebbles needs separating. Write the method you would use.

Done

RExplain why filter paper can separate sand from water, but cannot separate salt from water. Write one sentence.

Done

RExplain how you would choose a method for a mixture of solids and a liquid. Write one sentence.

Done