Question

An organic substance (M = 169 gram mol^–1) is dissolved in 2000 cm³ of water. Its osmotic pressure at 12°C was found to be 0.54 atm. If R = 0.0821 L atm K^–1 mol^–1, calculate the mass of the solute.

Answer 1

Given: T = 273.15 + 12 = 285.15 K
V = 2000 cm³ = 2 L 
M₂= 169 g mol^–1
R = 0.0821 L atm K^–1 mol^–1
π = 0.54 atm

To find: Mass of solute (W₂)

`pi=(W_2RT)/(M2V)`

`W_2=(piM_2V)/(RT)`

`W_2=(0.54xx169xx2)/(0.0821xx285.15)`

`W_2=182.52/23.4108=7.796 g`