0.102 g of an unknown compound dissolved in 100. mL of water has an osmotic pressure of 28.1 mmHg at 20^$\circ$C. Calculate the molar mass of the compound. A) 727 g/mol B) 663 g/mol C) 1.10 * 10² g/mol D) 1.15 g/mol E) 0.872 g/mol

Question

Quizplus · Accepted Answer

Using the osmotic pressure formula: π = MRT, where M is the molar concentration of the solute, R is the gas constant, and T is the temperature in kelvins. Rearranging this formula gives M = π/RT.

First convert the temperature to kelvins: 
20°C + 273.15 = 293.15 K

Next, convert the osmotic pressure from mmHg to atmospheres:
28.1 mmHg x (1 atm/760 mmHg) = 0.0369 atm

Now plug in the values to get the molar concentration:
M = 0.0369 atm / (0.0821 L atm/mol K x 293.15 K) = 0.00150 M

Finally, use the definition of molarity to find the molar mass:
molarity = moles solute / liters of solution
moles solute = molarity x liters of solution
moles solute = 0.00150 M x 0.1 L = 0.00015 mol

molar mass = mass of solute / moles solute
mass of solute = 0.102 g
molar mass = 0.102 g / 0.00015 mol = 680 g/mol

Therefore, the closest answer choice is B, 663 g/mol.

0102 G of an Unknown Compound Dissolved in 100 ∘\circ∘ C Calculate the Molar Mass of the Compound

0102 G of an Unknown Compound Dissolved in 100 $\circ$ C Calculate the Molar Mass of the Compound