3.1 Conservation of mass
5 exam questions worth 7 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
0 / 7
Magnesium ribbon is heated in a crucible open to the air. What happens to the mass of the solid?
Choose one answer.
Correct Not quite: the answer is It increases
Mark scheme
A
Model answer
A: oxygen from the air combines with the magnesium, so the solid gets heavier.
When 12.5 g of copper carbonate is heated, 8.1 g of copper oxide is left.
Calculate the mass of carbon dioxide given off.
Mark scheme
- 12.5 − 8.1 = 4.4 g (1)
Model answer
12.5 − 8.1 = 4.4 g of carbon dioxide.
Explain why the mass of a flask containing marble chips and hydrochloric acid decreases during the reaction.
Mark scheme
- carbon dioxide gas is produced (1)
- which escapes from the open flask (so it is not weighed) (1)
Model answer
The reaction produces carbon dioxide gas, which escapes into the air, so the mass on the balance falls.
A precipitation reaction is carried out in a sealed flask on a balance.
Explain why the mass stays the same.
Mark scheme
- no atoms are lost or made / atoms are rearranged (1)
- the flask is sealed so nothing can escape or enter (1)
Model answer
The flask is a closed system, so nothing can get in or out, and in the reaction atoms are only rearranged, so the total mass is unchanged.
2.4 g of magnesium burns completely in air to form 4.0 g of magnesium oxide.
Calculate the mass of oxygen that reacted.
Mark scheme
- 4.0 − 2.4 = 1.6 g (1)
Model answer
4.0 − 2.4 = 1.6 g of oxygen.
Found a mistake?