# If 100 mL of HCl gas at 300 K and 100 kPa dissolve in 20 mL of pure water, what is the concentration?

Aug 10, 2014

The concentration of the HCl is 0.20 mol/L.

There are two steps to this calculation.

1. Calculate the moles of HCl.
2. Calculate the molarity of the solution.

Step 1.

$P V = n R T$

$n = \frac{P V}{R T} = \left(100 \text{kPa" × 0.100"L")/(8.314"kPa·L·K⁻¹mol⁻¹" × 300"K}\right)$ = 4.01 × 10⁻³ mol

Step 2.

Molarity = "moles of [solute](http://socratic.org/chemistry/solutions-and-their-behavior/solute)"/"litres of solution" = (4.01 × 10⁻³"mol")/(0.020"L") = 0.20 mol/L

The concentration of the HCl is 0.20 mol/L.