Question

A student has synthesized a new compound (compound A, a nonelectrolyte). She uses osmotic pressure to determine the molar mass of compound A. She dissolves 0.50 g of compound A in water and prepares 15 mL of solution. At 25 C the osmotic pressure is 7.38 atm. Calculate the molar mass (g/mole) of compound A. Do not include a unit with your answer.

Answer 1

110g/mol is the molar mass of compound A

Step-by-step explanation:

The osmotic pressure of a solution could be obtained using the equation:

π = i*M*R*T -Solving molarity we can find the molar mass of the solute A-

Where π is osmotic pressure (7.38atm)

i is Van't Hoff's factor (1 for nonelectrolytes)

M is molarity (Our incognite)

R is gas constant (0.082atmL/molK)

T is absolute temperature (25°C + 273.15 = 298.15K)

Computing the values:

7.378atm = 1*M*0.082atmL/molK*298.15K

0.3018 mol/L is the concentration of the solution.

The volume of the solution is 15mL = 0.015L. Moles of the solute are:

0.3018 mol/L * 0.015L = 4.527x10⁻³ moles

Molar mass is the ratio between mass of the compound (0.50g) and the moles (4.527x10⁻³ moles). That is:

0.50g / 4.527x10⁻³ moles =

110g/mol is the molar mass of compound A