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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.
Answer
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Crushing the Tablet: Begin by crushing the tablet or dissolving it in water or dilute acid to obtain a solution.
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Testing for Lithium Ions:
- Use a clean metal wire and place it into a flame.
- Observe the flame color; a crimson flame indicates the presence of lithium ions.
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Testing for Carbonate Ions:
- Add dilute hydrochloric acid to the solution obtained earlier.
- Look for effervescence, which is the release of gas (carbon dioxide) indicating a carbonate ion.
- Pass the gas through limewater; if it turns cloudy, this confirms the presence of carbonate ions.
Step 2
Step 3
Calculate the percentage by mass of lithium carbonate in this tablet.
Answer
To find the percentage by mass of lithium carbonate, use the following formula:
Substituting in the values:
\text{Percentage by mass} = \left( \frac{700 \text{ mg}}{1200 \text{ mg}} \right) \times 100 \approx 58.33\%\n$$ Thus, the percentage by mass of lithium carbonate in the tablet is approximately **58.33%**.