# Osmotic Pressure moles NaCl exist as ion pairs

An aqueous solution is 1.00% NaCl by mass and has a density of 1.071 g/cm3 at 25°C. The observed osmotic pressure of this solution is 7.83 atm at 25°C.

(a) What fraction of the moles of NaCl in this solution exist as ion pairs?

%

(b) Calculate the freezing point that would be observed for this solution.

°C

https://brainmass.com/chemistry/stoichiometry/osmotic-pressure-moles-nacl-exist-ion-pairs-286851

#### Solution Preview

density = 1.071 g/cm3 = 1.071 kg/L

molar mass of NaCl = 23 + 35.45 = 58.45 g/mol

Kf of water = 1.86 C/m ---from book

pi = osmotic pressure

Basis : 1 kg of solution

V = vol. of solution = 1 kg / 1.071 kg/L = 0.9337 L

M = molarity = mol NaCl / liter solution

mol NaCl = 0.01(1 kg) (1000g/ 1 kg) ( 1 mol / 58.45 g/mol)

= 0.171 mol

M = 0.171 mol / 0.9337 L

= 0.183 M

pi = iMRT

i = pi / MRT

i ...

#### Solution Summary

The expert examines osmotic pressure moles NaCl exists as ion pairs.