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A student carried out an investigation to analyse the sulfate content of lawn fertiliser - HSC - SSCE Chemistry - Question 27 - 2003 - Paper 1
Question 27
A student carried out an investigation to analyse the sulfate content of lawn fertiliser. The student weighed out 1.0 g of fertiliser and dissolved it in water. 50 m... show full transcript
Worked Solution & Example Answer:A student carried out an investigation to analyse the sulfate content of lawn fertiliser - HSC - SSCE Chemistry - Question 27 - 2003 - Paper 1
Step 1
Calculate the percentage by mass of sulfate in the fertiliser.
Answer
To calculate the percentage by mass of sulfate in the fertiliser, we first need to determine the mass of sulfate ions in the barium sulfate precipitate. The formula for barium sulfate is BaSO₄.
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Calculate the molar mass of BaSO₄:
- Molar mass of Ba = 137.33 g/mol
- Molar mass of S = 32.06 g/mol
- Molar mass of O (4 atoms) = 16.00 g/mol × 4 = 64.00 g/mol
- Total molar mass of BaSO₄ = 137.33 + 32.06 + 64.00 = 233.39 g/mol
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Calculate the mass of sulfate in the precipitate:
- The mass of sulfate in barium sulfate can be calculated as follows:
- Mass of sulfate = (Mass of barium sulfate) × (Molar mass of sulfate / Molar mass of barium sulfate)
- Mass of sulfate = 1.8 g × (32.06 g/mol / 233.39 g/mol)
- Mass of sulfate ≈ 0.245 g
- The mass of sulfate in barium sulfate can be calculated as follows:
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Calculate the percentage by mass of sulfate in the fertiliser:
- Percentage by mass = (Mass of sulfate / Mass of fertiliser) × 100
- Percentage by mass = (0.245 g / 1.0 g) × 100 ≈ 24.5%.
Step 2
Evaluate the reliability of the experimental procedure used.
Answer
The reliability of the experimental procedure can be evaluated based on various factors:
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Repetition of experiments: If the experiment is repeated multiple times and yields consistent results, this indicates reliability. In this case, repeating the experiment with different samples of fertiliser would strengthen the reliability of the findings.
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Control of variables: Ensuring consistent conditions (like temperature, volume of solutions, and precise measurements) is crucial for reliability. Any variations could lead to discrepancies in results.
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Measurement accuracy: The precision of the weighing scale and the measurement of volumes should be considered. If these tools are inaccurate, they may introduce errors into the results.
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Judgement based on explanation: Better responses would assess whether the mass of sulfate obtained reflects the actual sulfate content in the fertiliser and discuss potential sources of error in the experiment, such as incomplete precipitation or measurement inaccuracies. Overall, the procedural reliability can be deemed acceptable if the above factors are properly managed.