A 0.035 M aqueous nitrous acid (HNO2) solution has an osmotic pressure of 0.93 atm at 22 °C. Calculate the percent ionization of the acid.

A different solution path:

π = (n/V)RT

(n/V) = π/RT

Note: n/V = moles of solute particles per liter.

n/V = (0.93 atm) / [(0.082057 L atm mol¯11) (295 K)]

n/V = 0.0384 mol/L

I will skip the rest of the solution.

I have a criticism of this solution (provided by someone on Yahoo Answers). The criticism: there is no explicit inclusion of the van 't Hoff factor, i.

You might ask "So where is the van 't Hoff factor included in the above calculation?"

It's included in the osmotic pressure of 0.93 atm. That value is NOT the osmotic pressure of a 0.035 M solution, it is the pressure of a 0.0384 M solution.

The van 't Hoff factor gets incorported into the pressure (thus hiding it) and I think that's a mistake in explaining how to solve these types of problems. Consequently, I think my solution path is better!