Question

The vapor pressure, P, of an aqueous solution of sodium chloride was determined at 23 C. Determine the mean ionic activity coefficient (y+_) for NaCl at each concentration, m.

m (mol/kg)     P (torr)
0                          23.2
0.5                      23.57
1                         23.2
1.5                       22.9

Answer 1

for calculations, we need to find first lonic strength of each solution : Nach dissociates completely as," Naci Nat tcr m Let mi concentration of Nat and cf lons. I = 1 {Cizi?

I - 1 | (+1) m + m(+1) where, I = ionic strength Ci Concentration of ions Zi= charge of in I= (m +m] # 2m for Naci, I am : corresponding to m (concentration) Values of I may be found as; (molk I (mol kg 1) When m= 1.5 log et = -0.51 (1) (1.5)'2 et = 0.237 Thus, the values of mean lonie coefficient goes on decreasing as we increase concentrator 0.5 0.5 1.5 . Log Y = -A343) I'2 Y = mean lorie cacturity coefficient A: Constant. Characterstu 0.51 3A 3B: charge on individual ions. When m=0 tog et = -0.51 / (+) (+) / (0)² FO when m=0.5 tog et = -0.51 (1) (0.5) Pt = 0.4361 when m=1 loght = -0.51 (1) (1) 2 Pt = 0.309