This set of Biophysics Multiple Choice Questions & Answers (MCQs) focuses on “Paper Chromatography – Set 2”.
1. Which amino acid has Rf value 0.73?
a) Leucine
b) Cystine
c) Proline
d) Alanine
View Answer
Explanation: 0.73 is the highest Rf value among all the amino acids. Leucine is the most nonpolar amino acid among all the amino acid. So amino acid Leucine has the Rf value 0.73.
2. Leucine and Isoleucine have almost the same Rf value.
a) True
b) False
View Answer
Explanation: Yes, Leucine and Isoleucine have almost the same Rf value. Because of the molecule as same molecular weight and same structure, differ only in one branching. Both of the amino acids have the same polarity, therefore, has almost the same Rf value.
3. Which of the following amino acid has the least Rf value?
a) Arginine
b) Cystine
c) Proline
d) Histidine
View Answer
Explanation: Histidine amino acid has the least Rf value. Arginine, Cystine, and Proline all 3 amino acids are less polar than Histidine. Therefore, Histidine having the highest polarity among these amino acids, have the least Rf value.
4. Choose the correct option according to their increase in Rf value.
a) Ser < Ala < Ile < His
b) Ala < Ile < His < Ser
c) His < Ser < Ala < Ile
d) Ala < Ile < His < Ser
View Answer
Explanation: The more polar the amino acid, the less Rf value it has in standard paper chromatography. According to the non-polarity the order is His < Ser < Ala < Ile. Therefore the order of increasing Rf value is His < Ser < Ala < Ile.
5. Detection of amino acid in a paper chromatography is a ____________ method.
a) constructive method
b) destructive method
c) regenerative method
d) constitutive method
View Answer
Explanation: Detection of amino acid in paper chromatography is a destructive method. This is because, after reacting with Ninhydrin reagent, form a compound that cannot be reversed to its initial form. Therefore, this method is degenerative.
6. After performing a standard paper chromatography experiment, you calculated Rf for each compound. You have got 4 values 0.8, 0.6, 0.4 and 0.5 respectively. Identify the compounds according to their Rf values.
a) 0.8 = A, 0.6 = B, 0.4 = C and 0.5 = D
b) 0.8 = D, 0.6 = C, 0.4 = B and 0.5 = A
c) 0.8 = D, 0.6 = C, 0.4 =A and 0.5 = B
d) 0.8 = C, 0.6 = D, 0.4 = A and 0.5 = B
View Answer
Explanation: It is a descending paper chromatography. Now, Rf value = (Distance traveled by the solute molecule from the origin/ Distance traveled by the solvent front from the origin of samples). So the highest distance travelled compound will have highest Rf value.
7. You have performed paper chromatography experiment of amino acids. After spraying with Ninhydrin, you have got a yellow color. What could be the amino acid?
a) Methionine
b) Proline
c) Leucine
d) Arginine
View Answer
Explanation: The overall reaction for the Ninhydrin reaction is α – amino acid + Ninhydrin = Aldehyde + Blue colored final complex+ H2O + CO2. But Proline is a secondary amino acid so the complex is yellow colored because of structural changes.
8. If the distance traveled by solute is 4 cm and the Rf value for that particular solute is 0.5, then what is the distance traveled by Solvent?
a) 2 cm
b) 4 cm
c) 6 cm
d) 8 cm
View Answer
Explanation: Rf value = (Distance traveled by the solute molecule from the origin/ Distance traveled by the solvent front from the origin of samples). So the distance traveled by Solvent front = 4/0.5 = 8 cm.
9. If the distance traveled by the solute molecule from the origin is 8 cm and the distance traveled by the solvent front from the origin of samples is 9 cm then what is the Rf value for that particular solute?
a) 0.889
b) 0.7779
c) 0.6669
d) 0.5559
View Answer
Explanation: Rf value = (Distance traveled by the solute molecule from the origin/ Distance traveled by the solvent front from the origin of samples). So the Rf value for that particular solute is = 8/9 = 0.889.
10. If the distance traveled by the solvent is 10 cm and the Rf value for that particular solute is 0.75, then what is the distance traveled by the solute in cm?
a) 5
b) 7.5
c) 8
d) 9
View Answer
Explanation: Rf value = (Distance traveled by the solute molecule from the origin/ Distance traveled by the solvent front from the origin of samples). So distance traveled be solute = 10*0.75 = 7.5 cm.
11. What do you infer from an Rf value?
a) The distance traveled by a molecule In TLC place
b) The polarity of the solute
c) The viscosity of the solute
d) The molecular weight of the solute molecule
View Answer
Explanation: Rf value is the ratio between the distance traveled by the solute molecule from the origin and distance traveled by the solvent front from the origin of samples. Therefore, from a given Rf value the distance traveled by a molecule In TLC place can be determined.
12. Imagine two compound X and Y. They have traveled 7 and 9 centimeters respectively in a standard TLC plate. If the Rf value for the compound X is 0.6364, then what is the Rf value for compound Y?
a) 0.444
b) 0.625
c) 0.729
d) 0.8182
View Answer
Explanation: We know Rf value = (Distance traveled by the solute molecule from the origin/ Distance traveled by the solvent front from the origin of samples). So, distance traveled by the solvent front is = 7/0.6364 = 11 cm (calculated from given information about X). Therefore, Rf value for compound Y is = 9/11 = 0.8182.
13. The following image is a conceptual diagram of radial paper chromatography. A mixture of 4 samples was spotted on the center of a paper, made of nonpolar constituents. After the completion of this experiment, 4 spots were found as shown in the diagram. What is the most polar and least polar component of the mixture?
a) The most polar component is B and the least polar component A
b) The most polar component is C and the least polar component A
c) The most polar component is D and the least polar component A
d) The most polar component is A and the least polar component C
View Answer
Explanation: In radial paper chromatography the paper itself is circular and the sample is loaded in the center. Now, the paper is made of nonpolar compounds, therefore, due to non-polar with non-polar interaction, the non-polar compound will move the least distance. So here the most polar component is D and the least polar component A.
14. When do we expose the paper (after chromatography) to the UV light for spot development?
a) Hydrocarbon separation
b) Ninhydrin reagent
c) Basic KMnO4
d) Sulfuric acid
View Answer
Explanation: Hydrocarbon absorbs UV light at 302 nm. So they are exposed to UV light for detection. There is no other way to detect hydrocarbon.
15. Which of the following mobile phase is used to separate hydrocarbons through paper chromatography?
a) Butanol + Acetic Acid + Water
b) Hexane + Chloroform + Acetic acid
c) 96% Ethanol + water
d) Ethyl Acetate + propanol
View Answer
Explanation: The Butanol + Acetic Acid + Water is used to separate amino acids. Whereas, the solvent with Hexane + Chloroform + Acetic acid is used to separate hydrocarbons. The solvent with 96% Ethanol + water is also used to separate amino acids.
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