chemistry : class12 Viscosity of Polymer Solutions : Macromolecular colloids : Surface Chemistry MCQ Questions and Answers
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Viscosity of Polymer Solutions
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MCQ Questions
1. A polymer solution has viscosity η = 1.50 mPa·s, while the pure solvent has viscosity η₀ = 1.00 mPa·s. If the polymer concentration is 0.020 g dL⁻¹, what is the reduced viscosity ηsp/c?
A.
10 dL g⁻¹
B.
20 dL g⁻¹
C.
25 dL g⁻¹
D.
50 dL g⁻¹
Correct Answer:
25 dL g⁻¹
Explanation:
The relative viscosity is ηr = η/η₀ = 1.50. Therefore, the specific viscosity is ηsp = ηr − 1 = 0.50. The reduced viscosity is ηsp/c = 0.50/0.020 = 25 dL g⁻¹.
2. Which limiting expression gives the intrinsic viscosity of a polymer solution?
A.
[η] = lim(c→∞)(ηsp/c)
B.
[η] = lim(c→0)(ηsp/c)
C.
[η] = lim(c→0)(ηr/c²)
D.
[η] = lim(c→∞)(ln ηr/c)
Correct Answer:
[η] = lim(c→0)(ηsp/c)
Explanation:
Intrinsic viscosity is defined as the limiting value of the reduced viscosity as polymer concentration approaches zero: [η] = lim(c→0)(ηsp/c). It reflects the hydrodynamic contribution of isolated polymer molecules.
3. According to the Huggins equation, [η] can be obtained by extrapolating which quantity to zero polymer concentration?
A.
ηsp
B.
ηr
C.
ηsp/c
D.
c/ηsp
Correct Answer:
ηsp/c
Explanation:
The Huggins equation is ηsp/c = [η] + kH[η]²c. A plot of ηsp/c against c has an intercept equal to the intrinsic viscosity [η] when c approaches zero.
4. For a dilute polymer solution, the Huggins relation is ηsp/c = [η] + kH[η]²c. What does the intercept of a plot of ηsp/c versus c represent?
A.
The solvent viscosity η₀
B.
The relative viscosity ηr
C.
The intrinsic viscosity [η]
D.
The polymer concentration at infinite dilution
Correct Answer:
The intrinsic viscosity [η]
Explanation:
Setting c = 0 in the Huggins equation eliminates the concentration-dependent term, leaving ηsp/c = [η]. Thus, the intercept directly gives intrinsic viscosity.
5. The Kraemer equation for dilute polymer solutions is written as ln ηr/c = [η] − kK[η]²c. Which graphical procedure determines [η] using this relation?
A.
Plot ln ηr/c against c and use the intercept
B.
Plot ln ηr against 1/c and use the slope
C.
Plot ηr/c against 1/c and use the intercept
D.
Plot c/ln ηr against c² and use the slope
Correct Answer:
Plot ln ηr/c against c and use the intercept
Explanation:
In the Kraemer equation, ln ηr/c varies linearly with c, and the value at c = 0 is [η]. Therefore, the intercept of a plot of ln ηr/c versus c gives the intrinsic viscosity.
6. For a polymer in a particular solvent at constant temperature, the Mark–Houwink equation is [η] = KM^a. If a is positive, what happens to intrinsic viscosity when the polymer molar mass increases?
A.
It decreases inversely with molar mass
B.
It remains independent of molar mass
C.
It increases as a positive power of molar mass
D.
It becomes zero above a critical molar mass
Correct Answer:
It increases as a positive power of molar mass
Explanation:
The Mark–Houwink relation [η] = KM^a shows that, for positive a, intrinsic viscosity increases with molar mass according to M^a. Larger polymer molecules contribute greater hydrodynamic resistance.
7. Two polymer samples have the same chemical composition and are measured in the same solvent at the same temperature. Sample P has a higher intrinsic viscosity than sample Q. According to the Mark–Houwink relation, which conclusion is most justified when the same K and a apply?
A.
Sample P has the lower molar mass
B.
Sample P has the higher molar mass
C.
Both samples must have identical molar masses
D.
The solvent viscosity of sample P must be higher
Correct Answer:
Sample P has the higher molar mass
Explanation:
With identical K and positive a, [η] increases with molar mass through [η] = KM^a. Hence, the sample with the larger intrinsic viscosity has the larger molar mass.
8. A polymer solution exhibits a larger intrinsic viscosity in solvent X than in solvent Y at the same temperature. What is the most appropriate interpretation?
A.
Polymer coils are hydrodynamically more expanded in solvent X
B.
Polymer chains are necessarily chemically degraded in solvent X
C.
The polymer concentration is necessarily greater in solvent X
D.
The solvent viscosity must be zero in solvent X
Correct Answer:
Polymer coils are hydrodynamically more expanded in solvent X
Explanation:
Intrinsic viscosity depends on the effective hydrodynamic volume of polymer molecules. A higher value generally indicates greater coil expansion or stronger polymer–solvent interaction in solvent X.
9. At sufficiently low polymer concentrations, which viscosity quantity approaches a finite concentration-independent value characteristic of the polymer, solvent, and temperature?
A.
The solvent viscosity η₀
B.
The intrinsic viscosity [η]
C.
The polymer concentration c
D.
The relative viscosity ηr without dilution
Correct Answer:
The intrinsic viscosity [η]
Explanation:
As concentration tends to zero, the reduced viscosity ηsp/c approaches the intrinsic viscosity [η]. This limiting quantity characterizes the hydrodynamic behavior of the polymer under specified conditions.
10. A polymer solution gives ηsp/c values of 80, 70, and 60 dL g⁻¹ at progressively lower concentrations. What is the most reasonable estimate of its intrinsic viscosity from these data?
A.
A value smaller than 60 dL g⁻¹
B.
Exactly 80 dL g⁻¹
C.
A value obtained by extrapolating the trend to zero concentration, likely below 60 dL g⁻¹
D.
The arithmetic mean, 70 dL g⁻¹, without any extrapolation
Correct Answer:
A value obtained by extrapolating the trend to zero concentration, likely below 60 dL g⁻¹
Explanation:
For many polymer solutions, reduced viscosity decreases as concentration decreases because intermolecular contributions become smaller. The intrinsic viscosity is the zero-concentration intercept, so the trend must be extrapolated rather than represented by one measured value.
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