Question

Determine the osmotic pressure of a solution prepared by dissolving 35 mg of K2SO4 in 4 litre of water at 25° C, assuming that it is completely dissociated.

Answer 1

Answer:

Given that: Mass of K

2

SO

4

,w=25mg=0.025g

Volume V=2L

T=25+273=298K

The reaction of dissociation of K

2

SO

4

:

K

2

SO

4

→2K

+

+SO

4

2−

Number if ions produced = 2+ 1 = 3

So van’t Hoff factor i=3

Use the formula of Osmotic pressure as:

π=i.

V

n

RT

π=i.

MV

w

RT

where R= Gas constant = 0.0821L atm K

−1

mol−1

Molar mass of K

2

SO

4

,M=2×39+1×32+4×16=174g/mol

Upon substitution we get:

π=3×

174×2

0.025

×0.0821×298

π=5.27×10

−3

atm