Standard solutions of sodium hydroxide, NaOH, must be kept in airtight containers - VCE - SSCE Chemistry - Question 9 - 2016 - Paper 1

The balanced equation for the complete reaction between carbonic acid and sodium hydroxide is:

$H₂CO₃(aq) + 2NaOH(aq) \rightarrow Na₂CO₃(aq) + 2H₂O(l)$

To calculate the amount of CO₂ that entered the container, we can use the ideal gas law and concentration:

1. Calculate the volume of air that entered the container, which is the volume of the container not filled with the NaOH solution: $V_{air} = 10.00 \text{ L} - 9.90 \text{ L} = 0.10 \text{ L}$

2. Calculate the moles of CO₂ in the air: $n(CO₂) = ext{concentration} \times V_{air} \\ n(CO₂) = 0.0400 \% \times 0.10 \text{ L} \frac{1 ext{ mol}}{100 ext{ L}}$ $= 4.00 \times 10^{-4} \text{ mol}$

3. The conditions of the air can also be used with the ideal gas equation: Given P = 101.3 kPa, V = 0.10 L, R = 8.31 L·kPa/(K·mol), T = 21.5 °C = 294.5 K, $n = \frac{PV}{RT} = \frac{101.3 \times 0.10}{8.31 \times 294.5} = 0.00400 ext{ mol}$

Thus, the amount of CO₂ that entered the container is approximately 0.00040 mol.