Practice important
Macromolecule Dissolution
MCQ questions and answers.
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MCQ Questions
1. A dry gelatin sample is added to cold water and allowed to stand before gentle warming. It first increases greatly in volume and then forms a colloidal sol. Which interpretation best explains this sequence?
A.
Gelatin undergoes swelling by solvent uptake before its macromolecular chains become sufficiently dispersed
B.
Gelatin undergoes precipitation first and is subsequently converted into a suspension by warming
C.
Water is chemically decomposed by gelatin during swelling and reforms during sol formation
D.
Gelatin particles first coagulate and then become electrically charged on heating
Correct Answer:
Gelatin undergoes swelling by solvent uptake before its macromolecular chains become sufficiently dispersed
Explanation:
Macromolecular substances commonly absorb solvent and swell before complete dissolution. In gelatin, solvent penetration and expansion of the polymer chains are followed by their dispersion throughout the medium to produce a colloidal sol.
2. Which condition most strongly favors the dissolution of a lyophilic macromolecule in a liquid medium?
A.
Strong attractive interactions between the macromolecule and solvent molecules
B.
Complete absence of interaction between the macromolecule and solvent
C.
Strong attraction only among macromolecules and negligible solvent penetration
D.
Conversion of the macromolecule into ions before contact with the solvent
Correct Answer:
Strong attractive interactions between the macromolecule and solvent molecules
Explanation:
Dissolution of lyophilic macromolecules is favored when solvent molecules strongly solvate or hydrate the polymer segments. These interactions enable solvent penetration, swelling, and eventual dispersion of the macromolecules.
3. A polymer dissolves readily in solvent X but only swells in solvent Y. What is the most appropriate conclusion regarding the two solvents?
A.
Solvent X has greater compatibility with the polymer than solvent Y
B.
Solvent Y has completely destroyed the polymer chains while solvent X has ionized them
C.
Solvent X necessarily has a higher boiling point than solvent Y
D.
Solvent Y must contain fewer molecules than solvent X
Correct Answer:
Solvent X has greater compatibility with the polymer than solvent Y
Explanation:
A compatible solvent can penetrate and solvate polymer chains sufficiently to separate and disperse them, producing dissolution. A less compatible solvent may enter the polymer and cause swelling but cannot disperse the chains completely.
4. Why does finely divided macromolecular material generally dissolve more rapidly than a large compact piece of the same material, assuming all other conditions remain unchanged?
A.
Its larger exposed surface permits faster solvent penetration and solvation
B.
Its molecular mass becomes lower during grinding
C.
Its polymer chains are automatically converted into smaller molecules
D.
Its electrical charge increases solely because of the increase in surface area
Correct Answer:
Its larger exposed surface permits faster solvent penetration and solvation
Explanation:
Fine division increases the contact area between the macromolecule and solvent. This facilitates solvent penetration into the material and accelerates swelling and subsequent dispersion, although it does not necessarily reduce molecular mass.
5. A macromolecular sol is prepared by adding a polymer gradually to water with continuous stirring. Adding the polymer too rapidly may produce lumps mainly because:
A.
The outer layers hydrate and form a swollen barrier that prevents water from reaching the inner portions
B.
Rapid addition immediately converts every polymer molecule into a crystalline solid
C.
Stirring causes permanent chemical degradation of the polymer
D.
Water loses its solvent character when several polymer chains are added together
Correct Answer:
The outer layers hydrate and form a swollen barrier that prevents water from reaching the inner portions
Explanation:
Macromolecules can hydrate at their surfaces and form a viscous swollen layer. If added too quickly, this layer can hinder further penetration of water, leading to lumps and incomplete dissolution.
6. Which observation most clearly distinguishes swelling of a macromolecule from its complete dissolution?
A.
The material increases in volume but remains as a coherent, swollen mass
B.
The material becomes uniformly dispersed throughout the solvent
C.
The solvent penetrates between the polymer segments
D.
The polymer develops stronger interactions with solvent molecules
Correct Answer:
The material increases in volume but remains as a coherent, swollen mass
Explanation:
Swelling involves solvent uptake and expansion while the macromolecular network or mass remains coherent. Complete dissolution requires separation and dispersion of the macromolecular chains throughout the solvent.
7. For a lyophilic macromolecule, increasing the temperature often accelerates dissolution because it primarily:
A.
Increases molecular mobility and speeds solvent penetration into the macromolecular mass
B.
Ensures that every polymer-solvent interaction becomes endothermic
C.
Reduces the molecular mass of each polymer chain
D.
Converts the macromolecule into a true electrolyte
Correct Answer:
Increases molecular mobility and speeds solvent penetration into the macromolecular mass
Explanation:
Moderate heating generally increases the mobility of solvent and polymer segments, allowing solvent to penetrate the macromolecular material more rapidly and promoting swelling and dispersion. It does not reduce polymer molecular mass or necessarily produce ions.
8. A hydrophilic macromolecule is placed in water containing a high concentration of an electrolyte and its sol separates. In terms of dissolution behavior, the most suitable explanation is:
A.
Electrolyte ions compete for water molecules and reduce hydration of the macromolecule
B.
The electrolyte always breaks every covalent bond in the polymer
C.
The macromolecule becomes a gas because its hydration energy becomes zero
D.
The electrolyte converts the polymer into a smaller molecular solute by hydrolysis in every case
Correct Answer:
Electrolyte ions compete for water molecules and reduce hydration of the macromolecule
Explanation:
Highly hydrated electrolyte ions can withdraw solvent molecules from the hydration layers surrounding a hydrophilic macromolecule. Reduced hydration weakens solvent compatibility and may cause separation of the macromolecular sol, a process related to salting out.
9. Two polymer samples have the same chemical composition, but sample P has a much higher molecular mass than sample Q. Under identical solvent conditions, which behavior is most likely for P during dissolution?
A.
P generally dissolves more slowly because its longer chains require more time for solvent penetration and disentanglement
B.
P always dissolves instantly because larger chains have greater solvent affinity
C.
P cannot absorb solvent because only low-molecular-mass polymers can swell
D.
P must dissociate into ions before it can form a colloidal solution
Correct Answer:
P generally dissolves more slowly because its longer chains require more time for solvent penetration and disentanglement
Explanation:
Higher-molecular-mass polymer chains are longer and more entangled. Although they may still be lyophilic and capable of swelling, solvent penetration and chain disentanglement usually proceed more slowly than in a lower-molecular-mass sample.
10. A protein is soluble in water at pH 7 but shows poor dissolution near its isoelectric pH. Which explanation is most directly related to macromolecule dissolution?
A.
At the isoelectric pH, reduced net charge lowers hydration and promotes association of protein molecules
B.
At the isoelectric pH, all peptide bonds are necessarily hydrolysed
C.
At the isoelectric pH, water molecules become nonpolar and cannot dissolve any substance
D.
At the isoelectric pH, the protein is converted into a low-molecular-mass electrolyte
Correct Answer:
At the isoelectric pH, reduced net charge lowers hydration and promotes association of protein molecules
Explanation:
Near the isoelectric pH, a protein has minimal net charge. Its hydration and electrostatic repulsion are reduced, so protein molecules associate more readily and dissolve less effectively in water.
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