A nonelectrolyte compound with a molar mass of 648 g mol^-1 was dissolved in enough water to make 250 mL of solution at 25 °C and produced an osmotic pressure of 27.4 mbar. Calculate the mass of the compound, in g, used to make this solution. A) 0.267 g B) 0.179 g C) 0.106 g D) 0.0873 g E) 0.236 g

Question

Quizplus · Accepted Answer

First, we need to use the van't Hoff factor, i, to calculate the number of moles of solute present in the solution:

π = iMRT

where π = osmotic pressure, M = molarity, R = gas constant, and T = temperature in Kelvin.

Since the solute is a nonelectrolyte, i = 1.

Converting the given temperature into Kelvin: 25 °C + 273.15 = 298.15 K

Substituting the given values into the equation:

27.4 mbar = (1)(M)(0.08314 L bar mol^−1 K^−1)(298.15 K)
M = 0.000963 M

Now we can use the molarity to calculate the number of moles of solute present in the solution:

n = MV
n = (0.000963 mol/L)(0.250 L)
n = 0.000241 mol

Finally, we can use the number of moles and the molar mass to calculate the mass of the compound:

mass = n x molar mass
mass = (0.000241 mol)(648 g/mol)
mass = 0.156 g

Therefore, the answer is B) 0.179 g (rounded to three significant figures).

A Nonelectrolyte Compound with a Molar Mass of 648 G