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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
Complete and balance the equation for the reaction.
Answer
The balanced equation for the reaction between potassium and water is:
ightarrow 2 ext{KOH} + ext{H}_2$$ This indicates that two moles of potassium react with two moles of water to produce two moles of potassium hydroxide and one mole of hydrogen gas.Step 2
Give two differences you would see between the reactions of potassium and lithium with water.
Answer
- Potassium reacts more vigorously than lithium, producing more heat and gas in a shorter time.
- Potassium ignites and produces a lilac flame, while lithium reacts more slowly and does not produce a 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
- Prepare the burette: Fill a burette with the potassium hydroxide solution and ensure there are no air bubbles.
- Add indicator: Place a few drops of a suitable pH indicator, like phenolphthalein, to the nitric acid in a conical flask.
- Titrate: Slowly add the potassium hydroxide solution from the burette to the nitric acid while swirling the flask.
- Observe the color change: Continue adding until the solution in the flask changes color, indicating neutralization.
- Record the volume: Note the volume of potassium hydroxide dispensed and repeat the process to find a consistent volume.
Step 4
Calculate the concentration of the nitric acid.
Answer
First, calculate the moles of potassium hydroxide used:
Since the reaction ratio between KOH and HNO₃ is 1:1, the moles of nitric acid are also 0.00525 moles.
To find the concentration of nitric acid:
ext{Concentration of HNO}_3 = rac{ ext{Moles of HNO}_3}{ ext{Volume}} = rac{0.00525 ext{ moles}}{0.025 ext{ dm}^3} = 0.21 ext{ mol/dm}^3