Answer is: osmotic pressure of aspirin is 0.025 atm.
m(C₉H₈O₄) = 45.0 ÷ 1000 mg/g = 0.045 g.
n(C₉H₈O₄) = m(C₉H₈O₄) ÷ M(C₉H₈O₄).
n(C₉H₈O₄) = 0.045 g ÷ 180 g/mol.
n(C₉H₈O₄) = 0.00025 mol.
c(C₉H₈O₄) = n(C₉H₈O₄) ÷ V(solution).
c(C₉H₈O₄) = 0.00025 mol ÷ 0.25 L.
c(C₉H₈O₄) = 0.001 M.
T = 25°C = 298.15 K.
R = 0.08206 L·atm/mol·K, universal gas constant.
p = c · R · T.
p = 0.001 mol/L · 0.08206 L·atm/mol·K · 298.15 K.
p = 0.025 atm.
