chemistry : class12 Dialysis of Macromolecules : Macromolecular colloids : Surface Chemistry MCQ Questions and Answers
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Dialysis of Macromolecules
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MCQ Questions
1. A solution containing a macromolecular colloid and dissolved sodium chloride is placed inside a dialysis bag and immersed in a large volume of distilled water. Which species will predominantly pass through the membrane during dialysis?
A.
Only the macromolecules, because they have higher concentration inside the bag
B.
Sodium ions and chloride ions, while the macromolecules are retained
C.
Macromolecules and sodium ions, but not chloride ions
D.
Neither sodium chloride nor macromolecules, because the membrane is impermeable to all solutes
Correct Answer:
Sodium ions and chloride ions, while the macromolecules are retained
Explanation:
A dialysis membrane contains very fine pores that allow small crystalloid ions such as Na+ and Cl− to diffuse through, but retain much larger macromolecules. Replacing the external water maintains the concentration gradient and promotes removal of the ions.
2. The principal basis for separating a macromolecular colloid from dissolved electrolytes by dialysis is the difference in their:
A.
Electrical charges only
B.
Densities and viscosities
C.
Particle sizes relative to the membrane pores
D.
Boiling points and vapour pressures
Correct Answer:
Particle sizes relative to the membrane pores
Explanation:
Dialysis depends primarily on selective permeability. Small electrolyte ions can pass through the semipermeable membrane, whereas the much larger macromolecular particles cannot pass through its pores.
3. A dialysis process is proceeding slowly even though the membrane is suitable and the external liquid is continuously stirred. Which change would most directly increase the rate of removal of a diffusible impurity?
A.
Replacing the external liquid repeatedly with fresh solvent
B.
Increasing the concentration of macromolecules inside the bag
C.
Using a membrane with smaller pores that still retains the impurity
D.
Reducing the temperature substantially
Correct Answer:
Replacing the external liquid repeatedly with fresh solvent
Explanation:
Continuous replacement of the external solvent maintains a low concentration of the diffusible impurity outside the dialysis membrane. This preserves the concentration gradient and increases the rate and extent of diffusion.
4. In the dialysis of a protein sol containing a small amount of ammonium chloride, which observation most convincingly indicates that dialysis is complete with respect to chloride ions?
A.
The protein sol becomes completely colourless
B.
The external liquid no longer gives a test for chloride ions
C.
The volume of the protein sol becomes equal to the volume of the external liquid
D.
The membrane becomes impermeable to water
Correct Answer:
The external liquid no longer gives a test for chloride ions
Explanation:
Chloride ions are small diffusible impurities and migrate through the membrane. When the external liquid no longer gives a chloride test after appropriate replacement, the chloride impurity has been substantially removed from the macromolecular sol.
5. Why is distilled water outside a dialysis bag often replaced several times during purification of a macromolecular colloid?
A.
To increase the size of the macromolecular particles
B.
To prevent the macromolecules from coagulating by increasing their charge
C.
To maintain a concentration gradient for the small diffusible impurities
D.
To make the membrane pores larger by hydration
Correct Answer:
To maintain a concentration gradient for the small diffusible impurities
Explanation:
As ions diffuse out, their concentration difference across the membrane decreases. Fresh distilled water lowers the external concentration again, maintaining the driving force for further diffusion while the macromolecules remain inside.
6. A membrane used for dialysis permits water, glucose, and sodium chloride to pass through but retains a protein. Which conclusion is most appropriate regarding the membrane?
A.
It behaves as a semipermeable membrane with a size-selective permeability
B.
It is permeable only to positively charged substances
C.
It allows only non-electrolytes to pass through
D.
It separates substances according to their boiling points
Correct Answer:
It behaves as a semipermeable membrane with a size-selective permeability
Explanation:
The membrane allows small molecules and ions such as water, glucose, and sodium chloride to pass, but blocks the larger protein molecules. This selective passage is the defining principle of dialysis.
7. A macromolecular sol contains two impurities: sodium chloride and a second polymer whose particles are smaller than the membrane pores but larger than sodium ions. If the membrane permits both species to pass, which statement is correct?
A.
Only sodium chloride will be removed because dialysis is restricted to electrolytes
B.
Both sodium chloride and the smaller polymer can diffuse out, while the retained macromolecule remains inside
C.
The retained macromolecule will diffuse out faster than sodium chloride
D.
No separation is possible because all colloidal particles are retained by dialysis membranes
Correct Answer:
Both sodium chloride and the smaller polymer can diffuse out, while the retained macromolecule remains inside
Explanation:
Dialysis is governed by particle size relative to membrane pores, not solely by whether a substance is an electrolyte. Any impurity sufficiently small to cross the membrane can be removed, whereas the larger target macromolecule is retained.
8. In an ideal dialysis experiment, the macromolecular sol is confined within a membrane while the surrounding liquid is continuously renewed. At equilibrium, which condition is expected for a freely diffusible ion?
A.
Its concentration becomes zero inside the membrane but remains high outside
B.
Its concentration becomes equal on both sides of the membrane, apart from effects of impermeable macromolecules
C.
It remains entirely inside because ions are colloidal particles
D.
Its concentration increases outside without any upper limit
Correct Answer:
Its concentration becomes equal on both sides of the membrane, apart from effects of impermeable macromolecules
Explanation:
For an ion that can freely cross the membrane, diffusion continues until its chemical potential is balanced across the membrane. In an ideal system this corresponds to equal concentrations, although charged macromolecules can modify ion distributions.
9. Which combination of changes would generally accelerate dialysis of a small ionic impurity from a macromolecular sol without causing the target macromolecule to pass through the membrane?
A.
Increase membrane area, stir the external liquid, and replace the external liquid frequently
B.
Decrease membrane area, stop stirring, and use a concentrated external impurity solution
C.
Use a membrane impermeable to the ionic impurity and increase the macromolecule concentration
D.
Lower the concentration gradient and reduce the temperature
Correct Answer:
Increase membrane area, stir the external liquid, and replace the external liquid frequently
Explanation:
A larger membrane area provides more diffusion surface, stirring reduces the boundary layer near the membrane, and frequent replacement maintains a high concentration gradient. These changes enhance removal of small ions while the size-selective membrane retains the macromolecule.
10. Electrodialysis is preferred over ordinary dialysis when rapid removal of ionic impurities from a macromolecular sol is required because it:
A.
Converts the macromolecules into crystalloidal particles
B.
Uses an applied electric field to accelerate the movement of charged impurities through the membrane
C.
Destroys the membrane pores and releases the macromolecules
D.
Prevents all ions from crossing the membrane while allowing proteins to pass
Correct Answer:
Uses an applied electric field to accelerate the movement of charged impurities through the membrane
Explanation:
Electrodialysis combines membrane separation with an electric field. Charged impurities migrate toward the oppositely charged electrode and cross suitable membranes more rapidly, while the larger macromolecules are retained.
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