Question

Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K₂SO₄ in 2 liter of water at 25°C, assuming that it is completely dissociated.

Determine the osmotic pressure of a solution prepared by dissolving 25 mg of K₂SO₄ in 2 liter of water at 25°C, assuming that it is completely dissociated. (mol. wt. of K₂SO₄ = 174 g mol⁻¹)

Answer 1

Given: K2SO4 dissolved (w) = 25 mg = 0.025 g

Volume of solution (V) = 2 L

Temperature (T) = 25°C = (25 + 273) K = 298 K

R = 0.0821 L atm K⁻¹ mol⁻¹

When K₂SO₄ is dissolved in water, K⁺ and \[\ce{SO^{2-}4}\] ions are produced.

\[\ce{K2SO4 -> 2K^+ + SO^{2-}4}\]

Total number of ions produced = 3

∴ i = 3

Molar mass of K₂SO₄ (M) = (2 × 39) + (1 × 32) + (4 × 16)

= 174 g mol⁻¹

Applying the following relation,

π = `i n/V RT`

= `i xx w/M xx 1/V RT`

= `3 xx 0.025/174 xx 1/2 xx 0.0821 xx 298`

= 5.27 × 10⁻³ atm