Science and Technology K–6 · Year 2

Breaking into smaller pieces: crushed chalk is still chalk

Material World (NSW 2017); Science understanding, Chemical sciences (ACARA v9)

PracticalLow risk

The idea

Snapping and crushing chalk makes smaller and smaller pieces without making a new material: the powder marks paper the same way, the pieces still add up to the same length, and the sealed bag weighs the same at every step.

What you need

2 sticks of blackboard chalk of the same colour per pair, and 2 spares
1 zip-seal sandwich bag per pair
A classroom balance reading to 0.1 g, zeroed before each weighing
A 30 cm ruler marked in millimetres, used both to measure and to crush
A sheet of black sugar paper and a hand lens per pair
A teaspoon, a jar lid and a few millilitres of water for pressing the powder back into a cake
A tray per pair to open the bag over
Recording table: step, mass of the sealed bag (g), total length of the pieces (mm), and whether the piece still marks the paper

How to do it

Weigh one stick of chalk on its own and record the mass to 0.1 g. Measure its length to the nearest millimetre. Rub it once on the black paper and look at the mark through the hand lens.
Seal the stick in the bag and weigh the bag with the chalk inside. Record this as the starting total.
Snap the chalk into about five pieces without opening the bag. Weigh the sealed bag again and record it.
Open the bag over the tray, lay the pieces end to end along the ruler and measure the total length. Rub one piece on the black paper.
Return every piece and crumb to the bag, seal it, and crush the pieces to powder with the flat of the ruler. Weigh the sealed bag again and record it.
Open the bag over the tray, tip out a teaspoon of powder, look at it through the lens and rub it on the black paper.
Press the rest of the powder into the jar lid with a few drops of water, level it, and leave it to dry until the next lesson. Try writing with the dried cake.
Repeat every step with the second stick so each pair has two sets of readings to compare.

What you should see

All three weighings of the sealed bag agree. Readings 0.1 g or 0.2 g apart are the balance's last digit moving, not chalk that has gone; a fall of more than 0.2 g means powder escaped while the bag was open, which is a handling fault, and the mass comes back when the tray is tipped in. The pieces laid end to end come within a few millimetres of the original length, a little long or a little short: breaking a stick into five pieces takes four snaps, which leave four pairs of rough ends that shed crumbs and do not butt together exactly, and the ruler is read to 1 mm. The difference is crumbs and rough ends, not lost matter, as the sealed-bag masses show. The mark on the black paper is the same colour at every step, the lens shows the powder to be the same stuff in smaller grains, and the dampened powder dries into a solid cake that writes on the black paper as the stick did. The learner knows it worked when the three sealed-bag masses agree within 0.2 g and the powder still marks the paper.

What changes

What you change: what is done to the chalk (whole stick, snapped into about five pieces, crushed to powder)
What you measure: mass of the sealed bag (g), total length of the pieces (mm), and whether the chalk still marks black paper
What you keep the same: the same stick inside the same sealed bag from start to finish
nothing added and nothing removed between weighings
the same balance, zeroed before every weighing
the bag opened only over the tray

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

Crushing chalk makes it lighter because the pieces are small.
The powder is a different material from the stick it came from.
Breaking something in half means there is half as much stuff as before.
Once chalk is powder nothing can be made of it again.

Safety card

Low riskLearners carry it out

Hazards

Chalk dust irritates eyes and airways
Dust on a hard floor is slippery
Chalk pressed hard can snap and flick a chip

Controls

Every snap and every crush happens inside the sealed bag
The bag is opened over a tray at bench height, away from faces, and no one blows on the powder
Spills wiped with a damp cloth rather than swept dry
Hands washed at the end

Note

No heat and no laboratory reagents: blackboard chalk is a nuisance dust rather than a hazardous substance, and its storage and use sit under the school's procedures from the NSW Department of Education Chemical Safety in Schools package. Record the activity on Primary School RiskAssess (riskassess.com.au).

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science and Technology K-6 Syllabus (2017), NESA. Current syllabus; NESA's timeline is 2026 plan and prepare, 2027 start teaching the 2024 syllabus. Code read from the official syllabus document on 2026-09-22.ST1-6MW-S ST1-1WS-S
Science and Technology K-6 Syllabus (2024), NESA. Implementation from 2027, so this code describes the future syllabus. Code read from the outcomes page on 2026-09-22.ST1-SCI-01 ST1-PQU-01 ST1-DAT-01
Australian Curriculum v9AC9S2U03AC9S2I01AC9S2I02AC9S2I03AC9S2I04AC9S2I05

Sources

The pages the author read to write this activity.

All Concept Studio activities