18. (2 pts) To confirm the identity of a spot on a TLC plate, you must: a. There
ID: 1044089 • Letter: 1
Question
18. (2 pts) To confirm the identity of a spot on a TLC plate, you must: a. There is no way to identify the compound in a TLC spot b. Compare the Rr of the spot with the values in the literature (Google it) c. Compare the Rr of the spot with the Rr of a known compound on another TLC plate d. Run a co-spot, in which you mix the known and the unknown and spot that on the plate. e. None of the above 19. The most critical parameter for success when doing TLC on silica gel plates is The solvent used to develop the TLC plate a. b. The geometry of the developing chamber C. Making sure that the analyte is spotted exactly 1 am from the bottom of the plate d. How rapidly the analysis is performed e. The length of the TCL plate VII. Separation of mixtures by extraction 20. Initially, all three compounds (acid, amine and neutral) were dissolved in ether. Mixing this organic phase with 5% HCl allowed which of these materials to enter the aqueous phase? a. The neutral compound b. The acid c. The amine d. None of the above 21-Mixing the organic phase with 5% NaOH allowed which of these materials to enter the aqueous phase? e. The neutral compound f. The acid g. The amine h. The organic phase i. None of the above 22. (2 pts) After having extracted with acid and base, mixing the organic phase with water allowed which of these materials to enter the aqueous phase? The neutral compound The acid The amine The organic phase None of the above a. b. c. d. e. 23. Recrystallizing the neutral product avoided which potential problem? a. Impurities in the product that could cause melting point elevation, causing you to misidentify it b. Impurities in your product that change its color, causing you to misidentify it c. Impurities in your product that could cause melting point depression, causing you to misidentify it d. All of the above e. None of the aboveExplanation / Answer
18.
Answer is option (d)
Explanation is within the statement.
19.
Answer is option (c)
Else, the solvent might wash down the spot.
20.
Answer is option (c)
RNH2 + H+ ------> RNH3+
Which is a salt and hence dissolves in water.
21.
Answer is option (f) The acid
RCOOH + NaOH ------> RCOONa
Sodium salt of carboxylate, which is a salt and hence dissolves in water.
22.
Answer is option (e) None of the above.
Neutral compound hardly dissolves in water.
23.
Answer is option (d)
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