---
title: "Conservation of Mass"
description: "Measure and provide evidence that the total weight of matter is conserved regardless of the type of change (heating, cooling, or mixing)"
canonical: https://lightmysky.com/learn/science/conservation-of-mass-mt_ehC1wsdmUz
source: https://lightmysky.com/learn/science/conservation-of-mass-mt_ehC1wsdmUz.md
retrieved: 2026-10-19
---

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# Conservation of Mass

Measure and provide evidence that the total weight of matter is conserved regardless of the type of change (heating, cooling, or mixing)

Subject: Science · Area: Matter & Materials · Ages 10 to 11
Page: https://lightmysky.com/learn/science/conservation-of-mass-mt_ehC1wsdmUz

## Ready when they can

- State the principle that matter is neither created nor destroyed during physical or chemical changes
- Describe an investigation weighing materials before and after a change to show mass is conserved
- Explain why dissolved sugar still contributes to the total weight even though it can't be seen

## Lesson: Conservation of mass

You already know that heating, cooling, and mixing can change how something looks. Ice can melt into water. Sugar can dissolve and seem to disappear into water. Here is the surprise: even when matter changes shape or seems to vanish, none of it is created or destroyed. If you weighed every bit before and after, the total weight would stay exactly the same.

*(drawing: The ice weighs 150g. Once it melts into water, it still weighs 150g. Only its shape changed.)*

**Example.** Priya sets a kitchen scale to zero with an empty cup on it, so the scale weighs only what goes in. She pours in 100g of water, then stirs in 20g of salt until it disappears from sight. The scale still reads 120g. The salt did not leave. It just spread out into pieces too small to see.

**Tip.** Whenever weight seems to disappear during a change, ask where the matter actually went. It may have turned into a gas, dissolved into a liquid, or just spread out, but it is still there somewhere.

When a weight seems to drop, ask where the matter went. A puddle dries up because its water turned into invisible vapor drifting in the air. A leaking beaker reads less because some water dripped out and never got weighed. Burning and fizzing make new materials, but the total still stays the same once you count every gas that forms or escapes. If the scale shows less, some matter left the scale; it was never destroyed.

**Recap.** Matter never disappears when it heats, cools, or mixes. It only changes form, so the total weight stays the same.

## Practice

24 questions on this page, each with its working shown.

## Needs first

- [Irreversible Changes](https://lightmysky.com/learn/science/irreversible-changes-mt_rbPioPELM1)
- [Matter Is Made of Particles](https://lightmysky.com/learn/science/matter-is-made-of-particles-mt_ylruY6VhOf)

## Opens up

- [Physical vs Chemical Changes](https://lightmysky.com/learn/science/physical-vs-chemical-changes-mt_1hgck6ucII)
- [Balancing Equations and Conservation of Mass](https://lightmysky.com/learn/science/balancing-equations-and-conservation-of-mass-mt_KUaPCEIA5f)