Question

Calculate the osmotic pressure of solutions in 1000 g of water at 25 C for the following solutes:

a) 0.1 mols of CaCl2
b) The same concentration of lignin at pH 12.
c) The same concentration of lignin at pH 5.

d) Sketch qualitatively the variation of the molar fractions (from 0.0 to 1.0) of dissociated and undissociated lignin with pH, assuming that pK = 9.

ANSWER: a) 7.31 atm   b) 4.88 atm   c) 2.44 atm

Need help solving, thanks!!!

Answer 1

As water has density 1g/mL so, 1000 g of water will have volume of 1000 mL or 1.0 L.

Also moles are 0.1 for all solutes, it is assumed to be a dilute solution and so, volume of solution is taken to 1 L.

Anan era)-0-1 Carl Ca u2 mol R: 0 082 7.33 atm

Answer d)

As pK for lignin is 9 so, both dissociated and undissociated forms will be equal at pH 9, so, molar fraction will be 0.5 each.

At pH below 9, molar fraction of undissociated form will be more and at pH above 9, dissociated form will be more.

So, qualitative graph will look like

useciaid o s 0.S lignn 0 I4