A 5*g5⋅g mass of polystyrene exerts an osmotic pressure of 1.21*kPa1.21⋅kPa at a temperature of 523*K523⋅K. What is the molecular mass of the polystyrene?

1 Answer
anor277
Jan 5, 2017

"Molecular mass of polystyrene"Molecular mass of polystyrene ~=≅ 7.4xx10^2*g*mol^-17.4×102⋅g⋅mol−1

Explanation:

Pi_"the osmotic pressure" = cRT

And thus Pi/(RT)=c

c=(1.21*cancel(kPa))/(1.01325*cancel(kPa*atm^-1))xx1/(0.0821*L*cancel(atm)*cancel(K^-1)*mol^-1xx523*cancelK)=0.0278*mol*L^-1.

Note the dimensional consistency. I changed the pressure into units of atmospheres, because this gives us a better idea of dimensionality. Of course, 1*atm-=101.3*kPa; such information should be given as supplementary material in any examination. Of course, you have to know how to use it and manipulate it.

And thus,
(2.05*g)/("Molecular mass of polystyrene")xx1/(0.100*L)=0.0278*mol*L^-1
So, finally, "Molecular mass of polystyrene"=(2.05*g)/(0.0278*mol*L^-1)xx1/(0.100*L)=737*g*mol^-1.

How many formula units of "styrene, "C_7H_8, compose this polymer?

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