Question

A 44.67 mL sample of a 0.200 M solution of barium nitrate is mixed with 18.26 mL of a 0.250 M solution of potassium sulfate. Assuming that all ionic species are completely dissociated and the temperature is 25ºC, what is the osmotic pressure of the mixture in torr?

Answer 1

1 mole of BaNO₃ produces 2 moles of ions

Molarity of ions in BaNO₃ = 2 x Molarity of BaNO₃ = 2 x 0.200 = 0.400 M = M₁

1 mole of K₂SO₄ produces 3 moles of ions

Molarity of ions in K₂SO₄ = 3 x Molarity of K₂SO₄ = 3 x 0.250 = 0.750 M = M₂

Molaroty of ions after mixing = (M_¹V₁ + M₂V₂)/(V₁+V₂) = (0.400 x 44.67 + 0.750 x 18.26)/(44.67 + 18.26)

= (17.868 + 13.695)/62.93 = 31.563/62.93 = 0.50156 M

P = MRT = 0.50156 x 0.0821 x 298.15 = 12.277 atm = 12.277 x 760 torr = 9330.52