This question is about lithium carbonate - AQA - GCSE Chemistry - Question 2 - 2019 - Paper 2
Question 2
This question is about lithium carbonate.
Lithium carbonate is used in medicines.
Figure 2 shows a tablet containing lithium carbonate.
Lithium carbonate contains... show full transcript
Worked Solution & Example Answer:This question is about lithium carbonate - AQA - GCSE Chemistry - Question 2 - 2019 - Paper 2
Step 1
Plan an investigation to show the presence of lithium ions and of carbonate ions in the tablet.
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Answer
To test for lithium ions:
Crush or dissolve a small piece of the tablet in water.
Clean a metal wire and place it in the solution.
Then, heat the wire in a roaring flame to observe the flame color.
The presence of lithium ions is indicated by a crimson flame color.
To test for carbonate ions:
Add a few drops of dilute hydrochloric acid to a separate portion of the crushed tablet.
Observe any effervescence or fizzing, indicating the release of carbon dioxide gas.
Pass the gas through limewater.
If the limewater becomes cloudy, this confirms the presence of carbonate ions.
Step 2
What name is given to mixtures like tablets?
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The name given to mixtures like tablets is 'formulations.'
Step 3
Calculate the percentage by mass of lithium carbonate in this tablet.
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Answer
To calculate the percentage by mass of lithium carbonate in the tablet, use the formula:
extPercentage=(mass of tabletmass of lithium carbonate)×100
Substituting the values:
Percentage=(1200mg700mg)×100=58.33%
Thus, the percentage by mass of lithium carbonate in the tablet is approximately 58.3%.
