Question

A 1.100 L sample of HCl gas at 25∘C and 732.0 mm Hg was absorbed completely in an aqueous solution that contained 7.114 g of Na2CO3 and 251.0 g of water.

a) what is the pH of the solution?

b) what is the freezing point of the solution?

c) What is the vapor pressure of the solution? (The vapor pressure of pure water at 25 ∘C is 23.76 mm Hg.)

Answer 1

a)

volume = 1.100 L

temperature = 298 K

pressure = 732 mmHg = 0.963 atm

P V = n R T

0.963 x 1.100 = n x 0.0821 x 298

n = 0.0433 mol

concentration = 0.0433 / 1.100 = 0.0394 M

pH = -log [H+] = -log (0.0394)

pH = 1.405

b)

molality = moles of solute / mass of solvent

            = 0.06711 / 0.251

            = 0.267 m

delta Tf = i x Kf x m

0 - Tf = 3 x 1.86 x 0.267

freezing point = - 1.49 oC

c)

Po - Ps / Po = Xsolute

23.76 - Ps / 23.76 = 0.00479

Ps = 23.65

vapour pressure of solution = 23.65 mmHg