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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 contai... 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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Preparation of the Sample: Crush the lithium carbonate tablet into a fine powder, ensuring it is homogeneous.
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Test for Lithium Ions:
- Using a clean metal wire, place it in a flame (preferably roaring).
- Dip the wire into the powdered tablet sample or dissolve it in water first.
- Hold the wire in the flame and observe the color produced; a crimson flame indicates the presence of lithium ions.
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Test for Carbonate Ions:
- In a test tube, add a small amount of dilute hydrochloric acid to the powdered tablet sample.
- Observe for effervescence or fizzing, which indicates the release of carbon dioxide.
- To confirm carbonate ions, bubble the gas through limewater and observe; if the limewater turns cloudy, it confirms the presence of carbonate ions.
Step 2
Step 3
Calculate the percentage by mass of lithium carbonate in this tablet.
Answer
To calculate the percentage by mass of lithium carbonate, use the formula:
Substituting in the given values:
- Mass of lithium carbonate = 700 mg = 0.700 g
- Total mass of tablet = 1.20 g
Substituting these values into the formula gives:
Thus, the percentage by mass of lithium carbonate in the tablet is 58.33%.