Question

Seawater has a salinity of 3.5%, i.e. 35 g of solid NaCl for one kilogram of seawater. For simplicity, assuming that all dissolved salts in seawater are NaCl rather than Na and Cl- ions and other species, what is the osmotic pressure between seawater and fresh water at 300K?

Answer 1

π = 29.3 atm

Step-by-step explanation:

The osmotic pressure π is given by

π = i MRT, where i=Vant Hoff factor =2 for NaCl ( 2 moles ions/mol NacL)

M = molarity

R = 0.0821 Latm/molK

T = temperature K

Assuming density of solution is 1 g/mL

M= 35 g/58.44 gmol / 1 L = 0.60 M

π = 2.0 x 0.60 mol/L x 0.0821 Latm/kmol x 300K = 29.3 atm