Question

Determine osmotic pressures at 30.0°C for each solution given. Assume complete dissociation of the salt. (a) 0.100 mol NaCl in 0.900 mol H2O (b) 0.100 mol Ca(NO3)2 in 0.900 mol H2O (c) 0.100 mol Al(NO3)3 in 0.900 mol H2O

Answer 1

a) osmotic pressure(P) = iCRT

i = vanthofffactor of NaCl = 2 (it gives 2 ions)

P = ?

C = concentration of solution = n*(1000/v in ml)   ( for water density = 1 g/ml)

= 0.1*(1000/(0.9*18))

= 6.17 M

R = solution constant = 0.0821 l.atm.k-1.mol-1

T = 273.15+30 = 303.15 k

P = 2*6.17*0.0821*303.15

= 307.12 atm

b)osmotic pressure(P) = iCRT

i = vanthofffactor of Ca(NO3)2 = 3 (it gives 3 ions)

P = ?

C = concentration of solution = n*(1000/v in ml)   ( for water density = 1 g/ml)

= 0.1*(1000/(0.9*18))

= 6.17 M

R = solution constant = 0.0821 l.atm.k-1.mol-1

T = 273.15+30 = 303.15 k

P = 3*6.17*0.0821*303.15

= 460.7 atm

C)
osmotic pressure(P) = iCRT

i = vanthofffactor of Al(NO3)3 = 4 (it gives 4 ions)

P = ?

C = concentration of solution = n*(1000/v in ml)   ( for water density = 1 g/ml)

= 0.1*(1000/(0.9*18))

= 6.17 M

R = solution constant = 0.0821 l.atm.k-1.mol-1

T = 273.15+30 = 303.15 k

P = 4*6.17*0.0821*303.15

= 614.25 atm