[stalebi]

A solid mixture contains MgCl2 and NaCl. When 0.5000 g of this solid is dissolved in enough water to form 1.000 L of solution, the osmotic pressure at 25°C is observed to be 0.4050 atm. What is the mass percent of MgCl2 in the solid? (Assume ideal behavior for the solution.)

This is what im trying to do. 

N=PV/RT=.0166mol of solute right?

let x=MgCl2 mass
y=NaCl mass

So we have

x+y=.5g
x/95.1+y/57.7=.0166mol

this doesnt give me a reasonable answer.  What am I doing wrong

[Borek]

N=PV/RT=.0166mol of solute right?

Ideal gas or osmotic pressure?

[Yggdrasil]

Remember than when MgCl₂ and NaCl dissolve, they dissociate into ions.  So one mole of NaCl will give you two moles of solute and one mole of MgCl₂ will give you three moles of solute.

[stalebi]

N=PV/RT=.0166mol of solute right?

Ideal gas or osmotic pressure?

Osmotic pressure, but doesnt the equation work for both?

Remember than when MgCl2 and NaCl dissolve, they dissociate into ions.  So one mole of NaCl will give you two moles of solute and one mole of MgCl2 will give you three moles of solute.

So should I set it up like this?

3x+2y=.0166 moles

and

95.1x+57.7y=.5g ?