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Chemical formulae, equations and calculations

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Question 1

Copper(II) carbonate decomposes when heated to form copper(II) oxide and carbon dioxide. The equation for the reaction is:

CuCO3(s)→CuO(s)+CO2(g) \text{CuCO}_3(\text{s}) \rightarrow \text{CuO}(\text{s}) + \text{CO}_2(\text{g}) CuCO3​(s)→CuO(s)+CO2​(g)

A student uses this method to investigate the reaction:

  • Step 1: Weigh a clean, dry crucible and record the mass.
  • Step 2: Add some green copper(II) carbonate.
  • Step 3: Reweigh the crucible and contents and record the new mass.
  • Step 4: Heat the crucible and contents for four minutes.
  • Step 5: Allow the crucible and contents to cool and then reweigh.
  • Step 6: Repeat steps 4 and 5 until the mass of the crucible and contents does not change.

The student performs the experiment four times (Trial 1 to Trial 4). The table below shows the results:

Mass measurements (in g\text{g}g)Trial 1Trial 2Trial 3Trial 4
Mass of empty crucible20.1518.9020.3519.72
Mass of crucible and copper(II) carbonate before heating24.5522.8025.1023.95
Mass of crucible and contents after heating for 4 minutes23.1021.6023.4022.71
Mass of crucible and contents after heating for a total of 8 minutes22.9521.4222.9022.45
Mass of crucible and contents after heating for a total of 12 minutes22.9521.4222.5522.45
a.

State why the mass of the crucible and contents decreases during heating.

[1]
b.

State the reason for Step 6.

[1]
c.

Explain in which trial the student should have heated for a fourth period of four minutes.

[2]

Chemical formulae, equations and calculations Questions

  1. IGCSE
  2. /Chemistry
  3. /Chemical formulae, equations and calculations