When 4.58 g of a nonelectrolyte solute is dissolved in water to make 725 mL of solution at 25 °C, the solution exerts an osmotic pressure of 875 torr. Required:
a. What is the molar concentration of the solution?
b. How many moles of solute are in the solution?
c. What is the molar mass of the solute?

a. 0.047 M

b. 0.6778 moles

c. 6.76 g/mol

Explanation:

The formula for osmotic pressure is:

π = i*M*R*T

Where:

i is the van't Hoff's factor (in this case is 1, because it is a non electrolyte solute)M is the molar concentrationR is the ideal gas constantT is the temperature in Kelvin

a.) So we solve for M:

875 torr ⇒ 785/760 = 1.15 atm25 °C ⇒ 25+273.16 = 298.16 K1.15 atm = 1 * M * 0.082 atm·L·mol⁻¹·K⁻¹ * 298.16 KM = 0.047 M

b.) We calculate the moles of solute, using the volume and molar concentration:

725 mL / 1000 = 0.725 L0.047 M * 0.725 L = 0.6778 moles

c.) We calculate the molar mass, using the mass and the number of moles:

4.58 g / 0.6778 moles = 6.76 g/mol

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