chemistry : class12 Lyophilic Character : Macromolecular colloids : Surface Chemistry MCQ Questions and Answers
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Lyophilic Character
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MCQ Questions
1. A lyophilic macromolecular sol is evaporated to dryness and the residue is redispersed in the same dispersion medium. Which observation most directly establishes its lyophilic character?
A.
The residue redisperses only after addition of an electrolyte
B.
The residue spontaneously forms a colloidal sol again on adding the dispersion medium
C.
The residue produces a precipitate that cannot be redispersed
D.
The residue becomes a true solution irrespective of the amount of medium added
Correct Answer:
The residue spontaneously forms a colloidal sol again on adding the dispersion medium
Explanation:
Lyophilic macromolecules have strong affinity for the dispersion medium. Therefore, after drying, they can usually be reversibly redispersed in the same medium to regenerate the colloidal sol.
2. Which molecular feature most plausibly accounts for the high stability of a lyophilic macromolecular sol in water?
A.
Complete absence of interaction between polymer segments and water
B.
Formation of a strongly solvated or hydrated layer around macromolecules
C.
Permanent conversion of every macromolecule into an ionic precipitate
D.
Removal of all solvent molecules from the vicinity of the polymer
Correct Answer:
Formation of a strongly solvated or hydrated layer around macromolecules
Explanation:
In a lyophilic sol, macromolecules interact strongly with the dispersion medium. In water, hydration layers form around the particles, helping prevent their aggregation and contributing to sol stability.
3. Two colloidal sols contain macromolecules of comparable size and concentration. Sol P is readily redispersed after drying, whereas sol Q is not. Which inference is most appropriate?
A.
P has greater affinity for the dispersion medium than Q
B.
Q must have a greater affinity for the dispersion medium than P
C.
Both sols necessarily have identical lyophilic character
D.
P must be a suspension while Q must be a true solution
Correct Answer:
P has greater affinity for the dispersion medium than Q
Explanation:
Ease of redispersion after drying is a characteristic of lyophilic systems. The stronger the interaction between the macromolecule and the dispersion medium, the more pronounced the lyophilic character generally is.
4. Which change would most directly weaken the lyophilic stabilization of a protein sol without chemically decomposing the protein?
A.
Increasing the extent of hydration of protein molecules
B.
Removing solvent molecules from the hydration sheath around the protein
C.
Increasing the compatibility between protein and solvent
D.
Allowing more solvent molecules to associate with exposed polar groups
Correct Answer:
Removing solvent molecules from the hydration sheath around the protein
Explanation:
Lyophilic stability depends strongly on solvation or hydration of the macromolecules. Removal or reduction of this solvent sheath decreases the protective interaction with the medium and can promote aggregation.
5. A macromolecular sol remains stable even when its particle charge is substantially reduced. Which explanation is most consistent with a lyophilic sol?
A.
Stability can arise from solvation of the macromolecules, not only from electrostatic repulsion
B.
A lyophilic sol contains no dispersion medium
C.
Reduced charge necessarily converts the sol into a gas
D.
Macromolecules remain dispersed only because their density is zero
Correct Answer:
Stability can arise from solvation of the macromolecules, not only from electrostatic repulsion
Explanation:
The stability of lyophilic colloids is primarily associated with strong interaction and solvation by the dispersion medium. Thus, their stability need not depend exclusively on particle charge.
6. Which sequence correctly ranks the expected affinity for water, from highest to lowest, for the following colloidal systems: gelatin sol, starch sol, and a typical lyophobic metal sol?
A.
Typical lyophobic metal sol > starch sol > gelatin sol
B.
Gelatin sol > starch sol > typical lyophobic metal sol
C.
Starch sol > typical lyophobic metal sol > gelatin sol
D.
Gelatin sol = typical lyophobic metal sol > starch sol
Correct Answer:
Gelatin sol > starch sol > typical lyophobic metal sol
Explanation:
Gelatin and starch are macromolecular substances with strong affinity for water and therefore form lyophilic sols. A typical lyophobic metal sol has comparatively little affinity for water.
7. A polymer dissolves in a solvent at the molecular level but, under another solvent condition, forms hydrated particles of colloidal dimensions. Which property determines whether the latter dispersion is lyophilic?
A.
The strength of interaction between the polymer and the dispersion medium
B.
The atomic number of the container material
C.
The color of the polymer powder
D.
The boiling point of the polymer alone
Correct Answer:
The strength of interaction between the polymer and the dispersion medium
Explanation:
Lyophilic character is defined by the affinity of the dispersed macromolecules for the dispersion medium. Strong polymer–solvent interaction leads to solvation and stabilizes the colloidal dispersion.
8. Why does a lyophilic macromolecular sol generally show greater resistance to irreversible coagulation than a comparable lyophobic sol?
A.
Its macromolecules are surrounded by a solvent layer that hinders close approach and aggregation
B.
Its particles are always larger than all suspension particles
C.
Its dispersion medium cannot interact with the dispersed phase
D.
Its particles contain no macromolecular chains
Correct Answer:
Its macromolecules are surrounded by a solvent layer that hinders close approach and aggregation
Explanation:
Strong affinity for the dispersion medium produces a solvated or hydrated envelope around lyophilic macromolecules. This envelope reduces direct particle contact and makes aggregation less irreversible.
9. A dried macromolecular sample fails to redisperse in the original solvent but redisperse after adding a substance that restores strong solvent–polymer interactions. What property was initially lost?
A.
Lyophilic character of the macromolecule toward that solvent
B.
The atomic mass of the dispersion medium
C.
The existence of the macromolecular chains
D.
The distinction between a colloid and a suspension
Correct Answer:
Lyophilic character of the macromolecule toward that solvent
Explanation:
Redispersibility depends on favorable interaction between the macromolecule and the dispersion medium. If that interaction is insufficient, the dried material cannot readily regenerate the lyophilic sol.
10. Which experimental combination provides the strongest evidence that a macromolecular dispersion is lyophilic rather than merely a mechanically dispersed suspension?
A.
Easy redispersion after drying together with pronounced solvent swelling
B.
Rapid sedimentation together with complete absence of solvent interaction
C.
Irreversible precipitation together with inability to absorb solvent
D.
Permanent separation of particles together with zero affinity for the medium
Correct Answer:
Easy redispersion after drying together with pronounced solvent swelling
Explanation:
Lyophilic macromolecules interact strongly with the dispersion medium. Their swelling or solvation and the ability to regenerate the sol after drying are characteristic evidence of lyophilic behavior.
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