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This question is about potassium and its compounds - AQA - GCSE Chemistry - Question 4 - 2017 - Paper 3
Question 4
This question is about potassium and its compounds. 4 (a) (i) Potassium reacts with water to produce potassium hydroxide solution and a gas. Figure 8 shows the app... show full transcript
Worked Solution & Example Answer:This question is about potassium and its compounds - AQA - GCSE Chemistry - Question 4 - 2017 - Paper 3
Step 1
Step 2
Give two differences you would see between the reactions of potassium and lithium with water.
Answer
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Potassium reacts more vigorously with water compared to lithium, leading to more vigorous bubbling and potentially an explosive reaction.
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Potassium produces a lilac flame when ignited, while lithium produces a crimson flame.
Step 3
Describe how a student could do titrations to find the mean volume of potassium hydroxide solution which would neutralise 25.00 cm³ of nitric acid.
Answer
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Prepare the potassium hydroxide solution in a burette.
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Place 25.00 cm³ of nitric acid in a conical flask and add a few drops of suitable indicator.
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Slowly release the potassium hydroxide from the burette into the conical flask while swirling the flask.
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Continue adding until the indicator changes colour, indicating neutralization.
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Record the volume of potassium hydroxide used and repeat the process to find the mean volume.
Step 4
Calculate the concentration of the nitric acid.
Answer
To find the concentration of nitric acid:
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Calculate the moles of potassium hydroxide used:
Moles of KOH = Volume (in dm³) × Concentration = 0.02625 , dm³ × 0.20 , mol/dm³ = 0.00525 , moles
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From the balanced equation, the mole ratio of KOH to HNO₃ is 1:1, so moles of HNO₃ = 0.00525.
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Calculate the concentration of HNO₃:
Concentration = Moles/Volume = 0.00525 , moles / 0.025 , dm³ = 0.21 , mol/dm³.