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 monomersconstitute the “average” molecule? The repeating unit of this
acrylic resin has the formula -CH2CH(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)
P = C*R*T
P = (mass/molar mass *volume) * R*T
0.325 = (47.7/M*0.5) *0.0821*(273+25)
M= 7182 gm

b)
Mass of monomer -CH2CHCN - =12+1*2+12+1+12+14
                                           = 53 gm

number of monomers = 7182/53 = 136

c)
total mass = density * volume
    = 1 gm/ml * 500 ml
     = 500 gm

mass of Acrylic = 47.7 gm
number of moles of Acrylic = mass/molar mass
= 47.7 / 7182
   =6.64*10^-3 mol

mass of water = 500 - 47.7 = 452.3 gm
moles of water = mass / molar mass
    = 452.3/18
     = 25.13 mol

mole fraction = 6.64*10^-3 / (6.64*10^-3 + 25.13)
    = 2.64*10^-4

use:
(PoA - P) /PoA = Mole fraction
(0.0313-P) /(0.0313) = 2.64*10^-4
P= 0.03129

d)
Osmometry is better because lowering in pressure is negligible for high molar masses.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.