Question

Q1)

9.47 g of a polystyrene sample was dissolved in acetone to make 135 mL of solution, and the osmotic pressure was measured to be 10.6 torr at 27°C. a) What is the molarity of the polystyrene solution? [Select] y x104M b) What is the approximate molar mass of the polystyrene? (Select] x 105 g/mol (Correct your answers to 3 sig. fig.)

Q2)

Take R = 0.08206 L atm/mol K or 8.314 J /mol K if you need

Thank you

Answer 1

1.

a. In order to ascertain the molarity of polystyrene solution, we are going to use the formula for osmotic pressure:

7 = IMRT

where,

T = osmotic pressure

In this case, since the value of osmotic pressure is in torr, we'll convert it into atm. 1 atm = 760 torr

So, osmotic pressure, in this case, becomes 0.0139 atm.

i = Van't Hoff factor, in case of polystyrene we'll take 1 as the value of i.

M = molarity or concentration of the solution

R = gas constant, 0.08206 L atm/mol K

T = Temperature, (27 + 273.15) = 300.15 K

Now, plugging the values into the equation of osmotic pressure:

0.0139 atm=1 XM X 0.08206 L atm mol-K-1 X 300.15K

M = 5.643 x 10-4 mol L-1

So, the molarity of the polystyrene solution is 5.643 X 10-4 M.

b. Now, since we have the concentration of the polystyrene solution, using the given mass of polystyrene we'll ascertain the approximate molar mass of polystyrene.

To ascertain the molar mass we're going to use the formula for molarity:

mass of solute Molarity = molar mass of solute Volume of solution in litres

9.47 g 5.643 x 10-4 mol L-1 = molar mass of polystyrene 135 x 10-3L

molar mass of solute = 1.243 x 10 g mol-1

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