Year 5 Science · Solutions and separating mixtures · Lesson 6.4

Year 5 Science: Sieving a mixture

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

6.4

Sieving a mixture

Year 5
M4: decide how a mixture of solids might be separated, using a sieve

Story. Tom has a box of sand and pebbles from the beach. “I want to get the sand out, but I don’t want to pick every pebble out by hand,” he says. His teacher says: “Use a sieve. Think about the size of the pieces.”

A mixture is two or more substances mixed together, without a chemical change. Some mixtures can be separated by their particle size.

A sieve has a mesh with holes. Small particles, such as sand, fall through the holes. Big particles, such as pebbles, stay on the top of the mesh.

A sieve over a tray: sand falls through the mesh, and pebbles stay on the top.

Particle	What happens in the sieve
sand	passes through the sieve
pebbles	stays on top of the sieve

Key ideas

A sieve separates a mixture of solids with different particle sizes.
Small particles pass through the holes of the sieve.
Large particles stay on the top of the sieve.
Sieving does not need water or heat.

Worked example 6.4.1

In a sieve, which particles pass through the holes: sand, or pebbles? Write the word.

Method. Read the sieve results.

Read the results. The sand passes through the sieve, but the pebbles stay on top.
sand passes
Name the particle. So the particles that pass through are the sand.
sand
Write the answer.
sand

Check. Small particles fall through the holes. ✓

Worked example 6.4.2

Why does sieving separate sand from pebbles? Write one word: size or colour.

Method. Think about why the sieve works.

Think about the particles. The sand particles are smaller than the holes, but the pebbles are bigger.
smaller
Choose the word. The separation depends on the size of the particles.
size
Write the answer.
size

Check. The sieve separates by size, not colour. ✓

Worked example 6.4.3

Does sieving need water to separate sand and pebbles? Write yes or no.

Method. Think about the method.

Think about the method. Sieving separates by particle size, so water is not needed.
not needed
Decide. So the answer is no.
no
Write the answer.
no

Check. Sieving is a dry method. ✓

Watch out

Watch out: a sieve separates by size, not by what the material is made of. A sieve will not separate salt from water, because salt dissolves.

Try it (with your teacher). With your teacher, put a small handful of dry sand and small pebbles (or dried peas and rice) into a sieve. Shake the sieve over a tray. Write which particles went through the holes, and which stayed on top.

Exam tip

Grown-up tip. Ask: “Which pieces went through? Which stayed on top? Why do you think that happened?” Let your child use the words size and particle.

Exercise 6D Sieving a mixture

FWhich mixture is separated by a sieve: a sand and pebble mixture, or salt water? Write the words.

Done

FWhat is a sieve made of, which lets small particles fall through? Write the word.

Done

FWhich particles stay on top of the sieve? Write the word.

Done

FWhich particles fall through the holes of the sieve? Write the word.

Done

FFill in the gap: a sieve separates particles of different ___. Write one word.

Done

FDoes a sieve need water to separate a dry mixture? Write yes or no.

Done

PSWhich method would separate a mixture of salt and water: sieving, or evaporating? Write the word.

Done

PSWhich method would separate a mixture of sand and pebbles, if the pebbles are much larger than the sand? Write the word.

Done

PSLook at the table in section 6.4. Write the word for the particles that stay on the sieve.

Done

PSWorking scientifically. Plan a fair sieving test. Name one thing that must stay the same in a fair test of sieving. Write one thing.

Done

RExplain why a sieve can separate sand from pebbles, but not salt from water. Write one sentence.

Done