Osmotic Pressure and Mass Calculation

Hi Sektor404,

Pi = MRT      Where Pi is the osmotic pressure, M = molarity, R = .08206, and T  = 36+273= 309K

1 atm = 101.3 kPa

782.7kPa * (1/101.3) = 7.72655 atm

7.72655 = M * (.08206) * 309
 
==> M = .3047 mol/L

And we have 2.05 L of the solution, Therefore we would need 2.05L * .3047 mol/L = .625 mol

Now to find the mass, we just need to take the molar mass of ribose multiply by the number of moles that we just found.

.625 * 150 = 93.75 g.

We would need to dissolve 93.75 g of ribose in 2.05L of water to make a solution that has osmotic pressure of 782.7kPa 

Hope this helps,
Laser

You are a life saver! Thanks so much I can finally understand it now!!