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)
What a learner can do afterwards
- 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
The lesson
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.
Priya weighs a cup with 100g of water, then stirs in 20g of salt until it disappears from sight. When she puts the cup back on the scale, it still reads 120g. The salt did not leave. It just spread out into pieces too small to see.
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.
Matter never disappears when it heats, cools, or mixes. It only changes form, so the total weight stays the same.
Watch it
Where it sits
This opens up
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.