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Mass loss during decomposition
A student investigated the thermal decomposition of copper carbonate.
Copper carbonate decomposes to form two products.
Figure 4 shows the apparatus.
Why does the mass of the contents of the test tube decrease in mass when copper carbonate is thermally decomposed?
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Marking points
- 1 States that a gaseous product escapes from the test tube.
Full-mark answer
A gaseous product, carbon dioxide, escapes from the open test tube, so the mass remaining in the test tube decreases.
Why this answer loses marks
Copper carbonate thermally decomposes.
This only restates what happens and does not explain the mass loss; a gaseous product must be identified as escaping from the test tube.