wunder beta⚖️ Conservation of Mass
Melt it, dissolve it, mix it — the amount of stuff never changes. Discover why mass is always conserved, even when things seem to vanish.
What you’ll learn
- Nothing DisappearsUnderstand that mass is the amount of matter and that conservation of mass means it is never made or destroyed.Mass is the amount of matter in something, measured with a balance or scale. Conservation of mass is the rule that matter is never made or destroyed in a change, so the total mass before always equals the total mass after.
- Weighing ChangesShow that melting and dissolving keep the total mass the same, and add the parts of a solution.Melting an ice cube keeps its mass the same, and dissolving a solute adds nothing and loses nothing. The mass of a solution equals the solute plus the solvent added together.
- The Sealed JarExplain why sealed reactions keep their mass while open ones seem to lose it as gas escapes.In a sealed bottle, a fizzy reaction traps its gas so the mass stays the same. In an open cup, the gas floats off into the air and the scale seems to drop — but the mass was never truly lost, just moved.
Questions this course answers
What does conservation of mass mean?
In any change, matter is never made or destroyed — it only moves or rearranges — so the total mass before equals the total mass after.
An ice cube weighs 50 grams. After it melts, the water weighs...
Melting only changes solid to liquid without adding or losing any stuff, so the water still weighs 50 grams.
You dissolve 20 grams of sugar into 100 grams of water. What does the sweet water weigh?
The mass of a solution equals the solute plus the solvent, so 100 grams plus 20 grams makes 120 grams.
Vinegar and baking soda fizz inside a sealed bottle on a scale. What happens to the mass?
The new gas is trapped inside the sealed bottle, so nothing leaves and the mass stays exactly the same.
In an open cup, the scale drops after the fizzing. Where did the mass go?
The new gas escaped into the air and carried its mass with it, so the scale reads less — but the mass was not truly lost.
If something seems to lose mass in a change, what should you suspect?
Mass is conserved, so a lower reading usually means a gas floated off into the air, carrying its mass away.
Grounded in trusted sources
- Royal Society of Chemistry
- BBC Bitesize
- Britannica
- American Chemical Society
Every Wunder lesson is built from real, reputable sources — never invented.
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