If 500 mL of HCl gas at 300 K and 100 kPa dissolve in 100 mL of pure water, what is the concentration?

Sep 26, 2014

The concentration of HCl is 0.200 mol/L.

You use the Ideal Gas Law to find the number of moles, and then you calculate the molarity.

$P V = n R T$

n = (PV)/(RT) = "100 kPa × 0.500 L"/("8.314 kPa·L·K"^-1"mol"^-1 × "300 K") = 0.020 05 mol (3 significant figures + 1 guard digit)

If there is no volume change when the HCl dissolves in the water, the volume of the solution is 100 mL.

Molarity = $\text{moles"/"litres" = "0.02005 mol"/"0.100 L}$ = 0.200 mol/L