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A student was given a sample known to be a mixture of magnesium oxide, MgO, and magnesium carbonate, MgCO₃, and asked to determine the mass of magnesium carbonate in the mixture - Scottish Highers Chemistry - Question 10 - 2023
Question 10
A student was given a sample known to be a mixture of magnesium oxide, MgO, and magnesium carbonate, MgCO₃, and asked to determine the mass of magnesium carbonate in... show full transcript
Worked Solution & Example Answer:A student was given a sample known to be a mixture of magnesium oxide, MgO, and magnesium carbonate, MgCO₃, and asked to determine the mass of magnesium carbonate in the mixture - Scottish Highers Chemistry - Question 10 - 2023
Step 1
Describe fully how the student could carry out this step.
Answer
To accurately measure a mass of 1.5 g of the mixture into a crucible using a balance, the student should follow these steps:
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Tare the Balance: Start by placing the empty crucible on the balance and press the tare button to zero the balance. This ensures that only the mass of the mixture will be measured without including the mass of the crucible.
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Transfer the Mixture: Carefully add the mixture into the crucible until the balance reads exactly 1.5 g. This can be done using a spatula or a funnel to avoid spills.
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Verify the Mass: After reaching 1.5 g, double-check the reading to ensure accuracy. If necessary, adjust the amount by adding or removing a small quantity of the mixture.
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Record the Mass: Once the desired mass is achieved, make a note of the measurement for reference in later calculations.
Step 2
Suggest why the student had to lift the lid from time to time.
Answer
The student had to lift the lid from time to time to allow carbon dioxide gas to escape during the heating process. This prevents the buildup of pressure inside the crucible, which could lead to danger or inaccurate results.
Step 3
Explain why a Bunsen burner is a suitable method of heating this reaction.
Answer
A Bunsen burner is suitable for this reaction because it provides a controllable and intense heat source, which is necessary for decomposing metal carbonates. The flame can be adjusted to reach the required temperature for the reaction, ensuring efficient and consistent heating.
Step 4
Calculate the mass, in g, of magnesium carbonate present in the mixture.
Answer
To calculate the mass of magnesium carbonate (MgCO₃) present in the mixture, first determine the mass lost during heating:
Mass lost = Mass before heating - Mass after heating = 1.598 g - 1.294 g = 0.304 g
Next, calculate the number of moles of CO₂ produced:
Number of moles of CO₂ = \frac{mass}{GFM} = \frac{0.304 g}{44.0 g/mol} = 0.00691 mol
Since 1 mol of MgCO₃ produces 1 mol of CO₂, the moles of MgCO₃ is also 0.00691 mol. Now calculate the mass of MgCO₃:
Mass of MgCO₃ = moles × GFM = 0.00691 mol × 84.3 g/mol = 0.582 g
Thus, the mass of magnesium carbonate present in the mixture is approximately 0.582 g.
Step 5
Complete a labelled diagram to show an apparatus suitable for the production of gas.
Answer
To complete the labelled diagram, the apparatus should include the following:
- A container for the reaction (like a flask) containing the mixture of magnesium oxide and magnesium carbonate, with excess acid added.
- An inverted measuring cylinder or gas jar filled with water to collect the carbon dioxide gas produced during the reaction.
- Tubing connecting the reaction flask to the measuring cylinder, allowing the gas to flow into the water.
- Ensure that all connections are sealed to prevent gas escape.
The diagram should clearly label these components.
Step 6
Suggest why carbon dioxide can be collected over water.
Answer
Carbon dioxide can be collected over water because it is relatively insoluble in water, which means it will rise above the liquid surface. This allows for the gas to be trapped in an inverted container without significant loss, making it practical for measurement.