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Question 54

Zinc carbonate decomposes when heated to form zinc oxide and carbon dioxide. The equation for the reaction is:

ZnCO3(s)→ZnO(s)+CO2(g) \text{ZnCO}_3(\text{s}) \rightarrow \text{ZnO}(\text{s}) + \text{CO}_2(\text{g}) ZnCO3​(s)→ZnO(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 zinc carbonate powder.
  • Step 3: Reweigh the crucible and contents and record the new mass.
  • Step 4: Heat the crucible and contents for five 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 A to Trial D). The table below shows the results:

Mass measurements (in g\text{g}g)Trial ATrial BTrial CTrial D
Mass of empty crucible25.3224.1825.0424.85
Mass of crucible and zinc carbonate before heating31.5230.2831.8431.05
Mass of crucible and contents after heating for 5 minutes29.8028.6529.9829.40
Mass of crucible and contents after heating for a total of 10 minutes29.3428.1429.4529.10
Mass of crucible and contents after heating for a total of 15 minutes29.3428.1429.4528.95
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 five minutes.

[2]

Chemical formulae, equations and calculations Questions

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