Osmotic Pressure Chemistry

Question

Calculate the osmotic pressure, P, of a 300 mL solution made by dissolving 80 g of NaOH at 27 ^oC. 

Answer 1

Before providing the calculation for osmotic pressure, it will be assumed that the final volume of the solution is 300 ml (0.3 L) and not that 80 g NaOH was added TO 300 ml. Also, this is a rather concentrated NaOH solution so the osmotic pressure will be quite high. Having said that...

Osmotic pressure = P = iMRT

i = van't Hoff factor = 2 for NaOH as it produces 2 ions (Na+ and OH-)

M = molarity = moles NaOH/L = 80 g x 1mol/40 g = 2 mol/0.300 L = 6.67 M

R = gas constant = 0.0821 Latm/Kmol

T = temperature in Kelvin = 27 + 273 = 300 K

P = (2)(6.67)(0.0821)(300) = 329 atm