Conservation of mass

Science · Matter & Materials · ages 10-11

Name ______________________ Date ____________

You stir a spoon of juice powder into a glass of water. The powder disappears from sight. What happened to the powder's matter?
- It was destroyed by the water
- It turned into heat and left the glass
- It is all still in the glass
A cup of hot tea with a tight lid cools on the table. Nothing is poured in and nothing spills. What happens to the amount of matter in the tea?
- It stays exactly the same
- It shrinks because the tea gets colder
- It grows because cooling adds matter
When an ice cube melts into water, what happens to the matter it's made of?
- Some of it is destroyed
- Some new matter is created
- All of it is still there
A scientist weighs a bowl of ice at 200g. She lets it melt completely and weighs it again. What will the scale most likely show?
- Less than 200g
- 200g
- More than 200g
Mia weighs 50g of salt and 100g of water separately, then pours them together in a cup. Type the total weight of the mixture in grams.
Answer: ______________
Omar pours 110g of milk into a mug that already holds 130g of hot cocoa. How much do the milk and cocoa weigh together now?
- 130g, because the milk disappears into the cocoa
- 260g, because liquids double when mixed
- 240g
Sam weighs a frozen juice pop at 80g while it is still solid. He lets it melt fully inside its wrapper. What will the scale show after it melts?
- Less than 80g, because melting removes matter
- 80g
- More than 80g, because liquid weighs more
Leo stirs 60g of sand into 140g of water. The mixture weighs exactly 200g. Why does the total match 60 plus 140?
- Because the water makes the sand heavier
- Because no matter is made or lost
- Because the sand shrinks to make room
Tomas pours juice into a tray and the full tray weighs 190g. Some juice sloshes over the side as he carries it to the freezer. Later the frozen tray weighs 170g. His sister says freezing destroyed 20g. What really happened?
- The spilled juice left the tray before freezing, so less matter went on the scale
- Freezing destroyed 20g of matter, like his sister said
- Ice always weighs less than juice
Aisha weighs an open cup of water at 180g and leaves it in a sunny window. Two days later the scale reads 120g. What is the best explanation?
- Some water turned into vapor and drifted away, so less was left on the scale
- The sun destroyed 60g of the water's matter
- The cup soaked up 60g and hid it

Answer key

For grown-ups. Fold this page away before handing over the rest.

Conservation of mass W1-mt_ehC1wsdmUz-s1

It is all still in the glass · Dissolving breaks the powder into pieces too small to see. They spread through the water, but none of the matter leaves the glass.
It stays exactly the same · Cooling only changes how warm the tea is. It never creates or destroys matter.
All of it is still there · The ice just changes into liquid water. No matter appears or disappears.
200g · Melting only changes the ice's state. The same matter is still there, so the weight stays 200g.
150 · Mixing does not add or remove matter, so the weights simply add together: 50g + 100g = 150g.
240g · Pouring milk into cocoa creates nothing and loses nothing. Together they weigh 130g + 110g = 240g.
80g · Melting only changes the juice from solid to liquid. The same matter stays in the wrapper, so the scale still reads 80g.
Because no matter is made or lost · Stirring things together never adds or removes matter, so the weight of the whole mixture is just the weights of the parts added together.
The spilled juice left the tray before freezing, so less matter went on the scale · The juice spilled before freezing, so it never got weighed with the tray. Freezing itself never destroys matter.
Some water turned into vapor and drifted away, so less was left on the scale · On a sunny windowsill, water slowly turns into vapor and leaves the cup. The missing 60g is in the air now; it was never destroyed.