Question

Calculate the osmotic pressure of a solution obtained by mixing 100 cm3 of 0.25 M solution of urea and 100cm3 of 0.1 M solution of cane sugar at 293 k .

Answer 1

We have to find the osmotic pressure of a solution obtained by mixing 100 cm³ of 0.25 M solution of urea and 100 cm³ of 0.1 M solution of cane sugar at 293 K.

solution : To find molarity of mixture, we should use formula, M₁V₁ + M₂V₂ = MV

here, M₁ = 0.25 M , M₂ = 0.1 M, V₁ = 100 cm³ , V₂ = 100 cm³ , V = 100 + 100 = 200 cm³

now, 0.25 × 100 + 0.1 × 100 = M × 200

⇒25 + 10 = M × 200

⇒35/200 = M

⇒M = 0.175 molar

Now osmotic pressure, π = CRT

where C is concentration (molarity of solution)

C = 0.175 molar , R = 0.082 L.atm/K/mol, T = 293K

so, π = 0.175 × 0.082 × 293 atm

≈ 4.2 atm

Therefore the osmotic pressure of the solution is 4.2 atm (approx).

Answer 2

piV =nRT

pi=nRT/V

pi=((0.25M×100cm^3+0.1×100сm^3)/200)×0.821)/0.2L

pi=21 atm