Write down the reaction time for the reaction of the pure CuCO₃ with HCl - NSC Physical Sciences - Question 5 - 2017 - Paper 2

To calculate the average rate of reaction, we can use the formula:

$ext{Average Rate} = -\frac{\Delta m}{\Delta t}$

Here, the mass decreases from 170.00 g to 169.76 g. Therefore:

$\Delta m = 170.00 - 169.76 = 0.24 \, g$

Thus, over the first 20 seconds:

$\Delta t = 20 \, s$

We obtain:

$\text{Average Rate} = -\frac{0.24}{20} = -0.012 \, g \, s^{-1}$

To find the percentage purity of the impure sample, we first find the mass of CO₂ produced.

The mass of the impure sample is:

$m = 170.00 - 169.78 = 0.22 \, g$

Now, applying the purity formula:

$\%\text{Purity} = \frac{m_{\text{pure}}}{m_{\text{impure}}} \times 100$

Substituting in the known values:

$\%\text{Purity} = \frac{0.22}{0.27} \times 100 \approx 81.48\%$

To calculate the maximum volume of CO₂ produced, we can use the molar volume of gas at standard conditions.

The number of moles of CO₂ produced is:

1. Mass of pure sample = 0.27 g
2. Molar mass of CO₂ = 44 g/mol

Using:

$n = \frac{m}{M} \Rightarrow n = \frac{0.27}{44} \approx 0.00613 \, mol$

The volume at standard conditions (22.4 L/mol):

$V = n \times 22.4 = 0.00613 \times 22.4 \approx 0.137 \, L$

To sketch the graph:

1. Draw the X-axis representing time in seconds (0 to 70 s).
2. Draw the Y-axis representing the volume of gas produced (starting from 0 L to the maximum volume calculated).
3. The graph should show a gradual increase in volume initially, reflecting the reaction rate.
4. Indicate the reaction time, which is between 42 and 50 seconds on the graph, where the reaction reaches completion.