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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. 1. Lithium carbonate conta... 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
To investigate the presence of lithium ions and carbonate ions in the tablet, follow these steps:
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Prepare the Tablet Sample:
- Begin by crushing the tablet into a fine powder or dissolve it in a small amount of water or dilute hydrochloric acid to ensure the complete release of ions.
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Test for Lithium Ions:
- Clean a metal wire and place it over a Bunsen burner until it is red-hot.
- Dip the wire into the powdered tablet or the solution obtained in step 1.
- Place the wire back into the flame and observe the color produced. A crimson flame would indicate the presence of lithium ions.
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Test for Carbonate Ions:
- Take a separate sample of the crushed tablet and add dilute hydrochloric acid to it. Look for effervescence (bubbles) which indicates a chemical reaction.
- Next, bubble the gas produced through limewater (a clear calcium hydroxide solution). If the limewater turns cloudy, it confirms the presence of carbonate ions, as carbon dioxide is a product of the reaction.
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 in the tablet, use the formula:
Given:
- Mass of the tablet = 1.20 g = 1200 mg
- Mass of lithium carbonate = 700 mg
So,
Thus, the percentage by mass of lithium carbonate in the tablet is approximately 58.3% (to two significant figures).