A student carried out a flame test on a sample of solid potassium chloride - Edexcel - GCSE Chemistry - Question 10 - 2023 - Paper 2
Question 10
A student carried out a flame test on a sample of solid potassium chloride.
The student followed this method.
step 1 dip a dry wooden splint into water
step 2 then... show full transcript
Worked Solution & Example Answer:A student carried out a flame test on a sample of solid potassium chloride - Edexcel - GCSE Chemistry - Question 10 - 2023 - Paper 2
Step 1
Explain one improvement that the student could make to their method to obtain a valid conclusion.
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Answer
One possible improvement would be to perform the experiment in a controlled environment where other ion tests do not interfere. For example, the student should use a clean splint for each sample and ensure that any residual water does not dilute the potassium chloride sample, thereby affecting the flame color.
Step 2
What colour should the student have seen in the flame if the test had been carried out correctly?
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Answer
The colour that the student should have observed in the flame, if the test had been performed correctly, is B, lilac. This is characteristic of potassium ions.
Step 3
Describe the test for chloride ions.
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To test for chloride ions, you can add a few drops of dilute nitric acid followed by silver nitrate solution to the sample. If chloride ions are present, a white precipitate of silver chloride (AgCl) will form.
Step 4
Calculate the mass of barium chloride that must be dissolved in water to make 25 cm³ of solution of this concentration.
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First, convert the volume from cm³ to dm³: 25 cm³ = 0.025 dm³. Using the formula:
Mass = Concentration × Volume
Mass = 83 g/dm³ × 0.025 dm³ = 2.075 g
Rounding to 2 significant figures, the mass of barium chloride required is 2.1 g.
Step 5
Write the ionic equation for this reaction.
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The ionic equation for the reaction between barium chloride and aluminium sulfate is:
