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

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

Mwt = wRT/PV = ((47.7*0.0821*298)/(0.325*0.5))

average molar mass of the polymer = 7181.653 g/mol

(b) How many monomers constitute the “average” molecule? The repeating unit of this

acrylic resin has the formula -CH2

Mass of repeating unit = 53

No of monomers = 7181.653 / 53 = 135.5 units

c) (P0-P/p0) = xB

no of moles of polymer = 47.7/7181.653 = 0.0066 mole

No of moles of water   = 500/18 = 27.7 mole

Total no of moles = 27.7+0.0066 = 27.7066

molefraction of solute xB = 0.0066/27.7066 = 0.000238

((0.0313-p)/0.0313) = 0.000238

Vapour pressure of solution p = 0.03129 atm

d) osmometry wouldbe preferable method for determination of high molar masses.

because lowering of vapor pressure is verry less .so that its not suitable.

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