# Magnesium ribbon is burned in a open crucible in air. A student notices that the mass of the crucible and its contents increases after the reaction. Explain why the mass increases, and state what would happen to the total mass of all substances involved if the reaction took place in a sealed container.

> Eduqas GCSE Chemistry — C3 Quantitative chemistry · Explain · 4 marks

> Magnesium burns in oxygen to form magnesium oxide. When burned in an open crucible, the mass of the solid increases.

## Mark scheme (4 marks)

1. Magnesium reacts with oxygen from the air
2. Oxygen is added to / gained by the solid, increasing its mass
3. In a sealed container the total mass would stay the same / remain constant
4. Because atoms are neither created nor destroyed / law of conservation of mass

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