Sulfur dioxide is a colourless, toxic gas that is soluble in water and more dense than air - Scottish Highers Chemistry - Question 5 - 2017

For collecting the gas, an inverted gas jar or a measuring cylinder could be used over water to collect the sulfur dioxide via upward displacement of air, as it is denser than air.

First, calculate the number of moles of sodium sulfite:

$\text{Number of moles} = \frac{0.40 g}{126.1 g/mol} \approx 0.00317 \text{ mol}$

Then, according to the reaction, 1 mole of Na2SO3 reacts with 2 moles of HCl. Thus:

$\text{Moles of HCl needed} = 0.00317 \text{ mol Na2SO3} \times 2 = 0.00634 \text{ mol HCl}$

Now calculate the number of moles of HCl available:

$\text{Moles of HCl} = \frac{50 cm^3 \times 1.0 mol/dm^3}{1000} = 0.050 \text{ mol}$

Since 0.00317 mol sodium sulfite requires 0.00634 mol hydrochloric acid, which is available, sodium sulfite is therefore the limiting reactant.

To calculate the overall enthalpy change for the reaction, we use the given reaction enthalpies:

$\Delta H_{reaction} = (\Delta H_{formation \, of \, products}) - (\Delta H_{formation \; of \; reactants})$

Substituting the relevant values:

Referring to the graph, at 10 °C, the solubility of sulfur dioxide is approximately 90 g l⁻¹.

The solubility of gases in water is influenced by their molecular geometry and polarity. Carbon dioxide (CO2) is a linear molecule and is non-polar, therefore it has weaker interactions with polar water molecules. In contrast, sulfur dioxide (SO2) has a bent shape, making it polar, which allows for better interactions with water molecules, facilitating greater solubility. The polarity of sulfur dioxide and its ability to form hydrogen bonds with water makes it much more soluble than carbon dioxide.