Acrylic resins are polymeric materials used to make warm yet lightweight garment

Question

Acrylic resins are polymeric materials used to make warm
yet lightweight garments. The osmotic pressure of a solution
prepared by dissolving 47.7 g of an acrylic resin in enough water
to make 500. mL of solution is 0.325 atm at 25°C.

(a) What is the
average molar mass of the polymer?

(b) How many monomers
constitute the “average” molecule? The repeating unit of this
acrylic resin has the formula -CH2
CH(CN)-. (c) What would be
the vapor pressure of the solution if the vapor pressure of pure
water at 25°C is 0.0313 atm? (Assume that the density of the
solution is 1.00 gcm-3

(d) Which approach (osmometry or the
lowering of vapor pressure) would you prefer for the determination
of very high molar masses such as those of acrylic resins? Why?

Explanation / Answer

Molecular formula: (C5O2H8)n
5·m(C) = (5 moles)(14 g/mol) = 70 g
2·m(O) = (2 moles)(16 g/mol) = 32 g
8·m(H) = (8 moles)(1.008 g/mol) = 8.064 g

Add them up:
m = 70 + 32 + 8.064 = 110.064 g /mole

for 47.7 g the no. moles = 47.7/110.064g = 0.433 mole

the no. of monomers = 0.433*6.023*1023 = 2.61*1023

a) the average molar mass of the polymer = 110.064 g /mole

b) the no. of monomers = 0.433*6.023*1023 = 2.61*1023

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