This question is about potassium and its compounds - AQA - GCSE Chemistry - Question 4 - 2017 - Paper 3

1. Reaction Speed: Potassium reacts more vigorously than lithium, producing hydrogen gas rapidly.

2. Flame Color: When potassium reacts with water, it produces a lilac flame, while lithium does not produce a flame.

1. Preparation: Fill a burette with potassium hydroxide solution and place a conical flask under it containing the nitric acid solution.

2. Indicator: Use an appropriate indicator to visualize the endpoint, such as phenolphthalein.

3. Titration Process: Slowly add the potassium hydroxide from the burette to the nitric acid while stirring continuously until the indicator changes color.

4. Reading the Burette: Record the volume of potassium hydroxide used at the point of color change.

5. Repeat: Repeat the titration two or three times to ensure accuracy and calculate the mean volume from the data collected.

To find the concentration of nitric acid, we first use the formula:

$ext{C}_1 imes ext{V}_1 = ext{C}_2 imes ext{V}_2$

Where:

• $C_1$ = concentration of potassium hydroxide (0.20 mol/dm³)
• $V_1$ = volume of potassium hydroxide used (26.25 cm³ = 0.02625 dm³)
• $C_2$ = concentration of nitric acid (unknown)
• $V_2$ = volume of nitric acid (25.00 cm³ = 0.02500 dm³)

Substituting the known values:

$0.20 imes 0.02625 = C_2 imes 0.02500$

Solving for $C_2$ gives:

$C_2 = \frac{0.20 imes 0.02625}{0.02500} = 0.21 ext{ mol/dm³}$

Therefore, the concentration of the nitric acid is 0.21 mol/dm³.