Question

Calculate the molarity of a solution containing KCl and water whose osmotic pressure at 38.0°C is 125 torr. Assume complete dissociation of the salt?

Answer 1

0,0032 mol/L

Explanation:

osmotic pressure law is `pi= i MRT`
where i =2 for complete dissociation of the salt in two ions
`R= 0,082 (L xx atm) /(mol xx K)`
T= 273+38 = 311 K
`p= (125 mmHg)/((760 mmHg)/(atm))=0.164 atm`
1mmHg = 1 torr
so `M= pi/(iRT)= (0.164atm)/(2 xx 0,082 (L xx atm) /(mol xx K) xx 311K) =0,0032 (mol)/L`