#### Question

# Question about osmotic pressure in chemistry?

I have to place the following solutions in order of increasing osmotic pressure but i have no idea how to calculate it, we never went over that in class and the book is of no help! Can someone help me please? Thanks you in advance for your answers!

A) 0.15 M C2H6O2

B) 0.15 M NaCl

C) 0.15 M CH3CO2H

#### Answer

In order to calculate the osmotic pressure, you will need the following equation:

P = MRTi, where:

P is the osmotic pressure of the solution

M is the molarity of solution

R is the gas constant (make sure the units here line up with the units of pressure)

T is the Kelvin temperature

i is the Van't Hoff factor (the number of particles in an ideal solution)

Since you're not given a temperature, I can't exactly do an example specifically of one of these, but let's say we were doing the first problem at 298 K:

P = (0.15 )(0.08206)(298)(1) = 3.66 atm

I hope this helped!

Osmotic Pressure = i * C * R * T , where i is the Van't hoff factor (i.e No. of particles generated by a solute in a solution), C is the concentration, R is Gas Constant, T is the temperature.

For the given choices, the concentrations of each are the same, hence the only determining factor of higher osmotic pressure will be the Van't hoff factor.

C2H6O2 doesn't exist. CH3COOH is Acetic acid which only dissociates partially in water because it's a weak acid.

NaCl is a strong electrolyte which will dissociate completely generating 2 particles (Na+ and Cl- ions), hence will have the highest osmotic pressure.

EDIT: Sorry, C2H6O2 is NOT ethanol and it doesn't exist.