Practice important
Coacervation
MCQ questions and answers.
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MCQ Questions
1. In coacervation of a macromolecular colloid, the separated coacervate phase is best described as:
A.
A dilute phase containing only the dispersing medium
B.
A macromolecule-rich liquid phase coexisting with a macromolecule-poor equilibrium phase
C.
A permanent solid precipitate formed by complete coagulation
D.
A gas phase formed by desolvation of the colloidal particles
Correct Answer:
A macromolecule-rich liquid phase coexisting with a macromolecule-poor equilibrium phase
Explanation:
Coacervation is liquid–liquid phase separation in which one phase becomes concentrated in macromolecules, forming the coacervate, while the other phase is relatively poor in macromolecules.
2. When oppositely charged macromolecules undergo complex coacervation, the principal initial driving interaction is:
A.
Electrostatic attraction between oppositely charged polymeric groups
B.
Repulsion between similarly charged polymeric groups
C.
Covalent cross-linking of every macromolecular chain
D.
Conversion of all macromolecules into small molecular solutes
Correct Answer:
Electrostatic attraction between oppositely charged polymeric groups
Explanation:
Complex coacervation commonly results from association of oppositely charged macromolecules, such as a polycation and a polyanion, through electrostatic attraction, producing a macromolecule-rich liquid phase.
3. A protein–polysaccharide system shows maximum tendency for complex coacervation at a particular pH. Which condition most plausibly explains this behavior?
A.
The protein and polysaccharide have charge states that favor strong opposite-charge association
B.
Both macromolecules are necessarily uncharged at every pH
C.
The pH causes complete hydrolysis of both macromolecules into monomers
D.
The pH eliminates all ionic interactions while increasing mutual repulsion
Correct Answer:
The protein and polysaccharide have charge states that favor strong opposite-charge association
Explanation:
The extent of complex coacervation depends strongly on pH because pH controls the ionization of macromolecular groups. A pH producing substantial opposite charges on the two components promotes their association and phase separation.
4. Why can increasing the concentration of added electrolyte suppress complex coacervation between oppositely charged macromolecules?
A.
The electrolyte increases the molecular mass of both macromolecules
B.
The electrolyte screens electrostatic attractions between the oppositely charged macromolecules
C.
The electrolyte converts the coacervate into a gas phase
D.
The electrolyte permanently removes all solvent from the system
Correct Answer:
The electrolyte screens electrostatic attractions between the oppositely charged macromolecules
Explanation:
Added ions reduce the effective electrostatic attraction by screening the charges on the macromolecular chains. As a result, association may weaken and the coacervate phase may diminish or disappear.
5. Which observation most clearly distinguishes coacervation from ordinary precipitation of a macromolecular colloid?
A.
Formation of a macromolecule-rich liquid phase that can separate into droplets
B.
Formation of an insoluble crystalline solid with no liquid character
C.
Complete conversion of the macromolecules into gases
D.
Permanent destruction of all macromolecular chains
Correct Answer:
Formation of a macromolecule-rich liquid phase that can separate into droplets
Explanation:
Coacervation produces a concentrated liquid coacervate phase, often visible as droplets, whereas ordinary precipitation generally produces a solid phase.
6. In simple coacervation of a macromolecular colloid, phase separation is most directly promoted by:
A.
Changing the solvent conditions so that macromolecule–solvent compatibility decreases
B.
Increasing the number of covalent bonds within every polymer chain
C.
Making all macromolecules carry identical charges and repel strongly
D.
Replacing the macromolecule with a low-molecular-mass gas
Correct Answer:
Changing the solvent conditions so that macromolecule–solvent compatibility decreases
Explanation:
Simple coacervation involves one macromolecular colloid and occurs when a change in solvent conditions, such as addition of a suitable nonsolvent, reduces solvation and causes separation into a polymer-rich liquid phase and a dilute phase.
7. A coacervate droplet is placed in contact with a dilute surrounding phase. At equilibrium, which statement is most appropriate?
A.
Macromolecules are present only inside the droplet and cannot exchange with the surrounding phase
B.
The droplet and surrounding phase have different macromolecular concentrations, but the relevant chemical potentials are equilibrated
C.
The droplet must contain no solvent because it is a precipitate
D.
The surrounding phase must have a higher macromolecular concentration than the droplet
Correct Answer:
The droplet and surrounding phase have different macromolecular concentrations, but the relevant chemical potentials are equilibrated
Explanation:
Coacervation gives two coexisting liquid phases with different compositions. Although the coacervate is macromolecule-rich, equilibrium requires equality of the appropriate chemical potentials across the phases, allowing dynamic exchange.
8. In a protein–polyanion complex-coacervation system, changing the pH causes the protein to lose the charge needed for attraction. The most likely result is:
A.
Enhanced coacervate formation because electrostatic attraction becomes stronger
B.
Suppression of complex coacervation because the necessary opposite-charge association weakens
C.
Formation of a gas phase from the protein
D.
Conversion of the polyanion into a metal crystal
Correct Answer:
Suppression of complex coacervation because the necessary opposite-charge association weakens
Explanation:
Complex coacervation depends on attractive interactions between oppositely charged macromolecules. Removing or greatly reducing the protein’s required charge decreases association and can prevent coacervate formation.
9. Which combination is most characteristic of complex coacervation rather than simple coacervation?
A.
One macromolecule, with phase separation caused only by cooling below its melting point
B.
Two oppositely charged macromolecules, with phase separation caused by their mutual association
C.
One volatile solute, with phase separation caused by evaporation into a gas
D.
Two neutral crystals, with phase separation caused by lattice formation
Correct Answer:
Two oppositely charged macromolecules, with phase separation caused by their mutual association
Explanation:
Complex coacervation involves at least two oppositely charged macromolecular species. Their electrostatic association produces a macromolecule-rich liquid phase, distinguishing it from simple coacervation.
10. Why is coacervation particularly useful for encapsulating a dispersed material in colloid-based systems?
A.
The liquid coacervate can deposit around dispersed particles and later be solidified or stabilized as a coating
B.
The coacervate instantly converts every dispersed particle into a gas
C.
Coacervation prevents any interaction between macromolecules and the dispersed material
D.
The coacervate is always a crystalline solid before contacting the dispersed material
Correct Answer:
The liquid coacervate can deposit around dispersed particles and later be solidified or stabilized as a coating
Explanation:
Because a coacervate is a concentrated liquid macromolecular phase, it can wet and surround dispersed particles. Subsequent stabilization of this layer enables colloid-based encapsulation.
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