AQA GCSE Chemistry 8462
Atomic Structure and the Periodic Table
Bonding, Structure, and the Properties of Matter
Chemical Analysis
Chemical Changes
Chemistry of the Atmosphere
Energy Changes
Organic Chemistry
Quantitative Chemistry
The Rate and Extent of Chemical Change
Using Resources
Quantitative Chemistry
Mass changes when a gas is involved, and measurement uncertainty
- 3 things to know
- Paper 1
Overview
Why a metal gains mass when heated in air and a carbonate loses mass when decomposed, apparent breaches of conservation of mass explained with particles, the effect of sealing the container, uncertainty from the range of repeats, accuracy, precision, repeatability and reproducibility, random and systematic errors, anomalous results, resolution and reading scales, and mean, median and mode.
What you need to know
Answer each one before you reveal it.
Explain why the mass of solid increases when a metal is heated in an open crucible in air.
Explain why the mass of solid falls when a metal carbonate is thermally decomposed in an open container.
Questions from this subtopic
Each one with the model answer underneath.
- 1
Explain why the mass of solid increases when a metal is heated in an open crucible in air.
Model answer
Oxygen from the air combines with the metal, so the oxide formed has the mass of the metal plus the mass of the oxygen added to it.
- 2
Explain why the mass of solid falls when a metal carbonate is thermally decomposed in an open container.
Model answer
Carbon dioxide is produced and escapes into the atmosphere, leaving the metal oxide as the only solid product.
- 3
Name the gas that escapes when calcium carbonate is heated strongly.
Model answer
Carbon dioxide.
- 4
Name the solid product left behind when copper carbonate is thermally decomposed.
Model answer
Copper oxide.
- 5
A student says the law of conservation of mass is broken because magnesium gains mass when it burns. Is the student right?
Model answer
No, because the oxygen taken from the air has mass, and once that is counted the total mass is unchanged.
- 6
24 g of magnesium is burned in air and 40 g of magnesium oxide is formed. Explain the increase in terms of particles.
Model answer
Oxygen particles from the air have bonded to the magnesium atoms, so 16 g of oxygen has been added to the solid on the balance.
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