This set of Dairy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Centrifugal Seperators”.
1. After centrifugation when sublimate settles, clear liquid_____________
a) can be allowed to rest
b) can be allowed to form crystals
c) can be decanted off
d) can be evaporated
Explanation: Centrifugation separates sublimate and whey. Once the sublimate settles after centrifugation, clear liquid can be decanted off.
2. After centrifugation, sublimate ______
a) dissolves completely
b) remain suspended in liquid
c) settles at bottom
d) depends upon pH of sublimate
Explanation: These particles can sediment at the bottom of the tube into what’s known as a pellet, and this isolated specimen, or the remaining solution, the supernatant, can be further processed or analyzed.
3. Which of the following is an effective way of purifying liquids containing suspensions?
d) separating funnel
Explanation: A suspension is a heterogeneous mixture containing solid particles that are sufficiently large for sedimentation .Liquids containing suspension can be purified using centrifugation.
4. Fine insoluble solid particles can be removed through which of the following process?
d) separating funnel
Explanation: Decantation is a process for the separation of mixtures, by removing a layer of liquid, generally one from which a precipitate has settled. Centrifugation helps in removal of fine insoluble particles in a solution.
5. Process quicker than filtration but not so effective is
d) fractional distillation
Explanation: Decanting is a process to separate mixtures. Decanting is just allowing a mixture of solid and liquid or two immiscible liquids to settle and separate by gravity. This process can be slow and tedious without the aid of a centrifuge.
6. Differential centrifugation relies on the differences in ______ of biological particles of different ___________
a) Size, density
b) Sedimentation rate, sizes and density
c) Size, structure
d) Mass, size
Explanation: Differential centrifugation is a process which is used to separate certain organelles from whole cells for further analysis of specific parts of cells. Differential centrifugation is a process based on the differences in the sedimentation rate of biological particles of different sizes and density.
7. Which of the following statements about the basic principle of sedimentation is False?
a) The denser a biological structure is, the faster it sediments in a centrifugal field.
b) The more massive a biological particle is, the slower it moves in a centrifugal field
c) The denser the buffer system is, the slower the particle will move in a centrifugal field
d) The greater the centrifugal force is, the faster the particle sediments
Explanation: Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. The statement is false because the more massive a biological particle is, the faster it moves in a centrifugal field.
8. Which of the following is/are the application of analytical centrifugation?
I. The determination of the purity of macromolecules.
II. The determination of the relative molecular masses of solutes in their native state.
III. The examination of changes in the molecular mass of supramolecular complexes.
IV. The detection of conformational changes.
a) I only
b) I and II only
c) I,II and III only
d) I, II, III and IV
Explanation: Analytical ultracentrifugation (AUC) is a versatile and powerful method for the quantitative analysis of macromolecules in solution. All of these are application of analytical centrifugation.
9. Which of the following is/are appropriate care and maintenance of centrifuges?
I. Proper balancing of centrifuge tubes.
II. Avoid long time exposure of the rotors to alkaline solution and acidic buffers.
III. Cleaning centrifuges and rotors with coarse brushes and then wash them with distilled or de-ionized water after every run.
IV. For overnight storage, the rotors are left upside down and then positioned in a safe and dry place.
a) I, II, III only
b) II, III and IV only
c) I, II, and IV only
d) II only
Explanation: Only option I, II and IV are appropriate care and maintenance of centrifuges. However, cleaning centrifuges and rotors with coarse brushes may cause damage to the protective layers of rotors. Therefore, option iii is wrong.
10. After centrifugation of milk, the supernatant is?
Explanation: After centrifugation of milk, the whey is left as the supernatant. A separator is a centrifugal device which aid in separation of milk into cream and skimmed milk.
11. What is the name of the machine that spins in order to separate out components making up a mixture?
b) Blood plasma
d) Centrifugation tube
Explanation: A centrifuge is a machine with a rapidly rotating container that applies centrifugal force to its contents, typically to separate fluids of different densities (e.g. cream from milk) or liquids from solids.
12. How does centrifugation work?
a) Through dripping particles
b) Through spinning
c) By keeping large particle in the center and smaller on the outside
d) By separating particles into different tubes
Explanation: The centrifuge works using the sedimentation principle, where the centripetal acceleration causes denser substances and particles to move outward in the radial direction. At the same time, objects that are less dense are displaced and move to the center.
13. If you were centrifuging whole milk, which would you expect to get flung further out from the center of the centrifuge?
a) The cream/fat
b) Both would be equally flung
c) The skim milk
d) Neither would be flung
Explanation: When spun, the heavier milk is pulled outward against the walls of the separator and the cream, which is lighter, collects in the middle. The cream and milk then flow out of separate spouts.
14. Which of the following scientist invented the centrifugal separator?
a) Gustaf de Laval
b) Donald ronholm
c) Luis pastuer
Explanation: From 1890 the separators built by Gustaf de Laval were equipped with specially designed conical discs, the patent on which had been granted in 1888.
15. The skimming efficiency of a separator consequently decreases with increased throughput. State true or false?
Explanation: The flow velocity through the separation channels will be reduced if the flow rate through the machine is reduced. Thus providing the fat globules more time to rise and be discharged through the cream outlet. The skimming efficiency of a separator consequently increases with decrease in throughput and vice versa.
Sanfoundry Global Education & Learning Series – Dairy Engineering.
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