Question

What is the osmotic pressure formed by dissolving 50.5 mg of aspirin (C9H8O4) in 0.500 L of water at 25°C?

Answer 1

π is osmotic pressure
C is concentration in moles/L
R is the gas constant (0.0821 L atm/mol K)
T is temperature in K

convert mg to moles using molar mass of aspirin (180 g/mol):
50.5 mg = 0.0505 g
0.0505 g * mol/180 g = 2.805e-4 mol

find molarity by dividing moles by liters:
2.805e-4 mol/0.500 L = 5.611e-4 mol/L

convert temperature to K:
25 C + 273 = 298 K

plug into π = CRT and solve for π:
π = 5.611e-4 mol/L (0.0821 L atm/mol K) (298 K)
π = 1.37e-2 atm