questions 4,7,8&9 the components of the mixture and the retention times of the s
ID: 572419 • Letter: Q
Question
questions 4,7,8&9
the components of the mixture and the retention times of the standard, identify each component of the mixture. Measure the areas of each peak and determine the relative mass percent of each component. (Molar absorptivities of the two components are about the same at 254 nm.) Questions 1. List throe factors that affect Re values in adsorption TLC. Explain. 2. Explain how to prepare sample solutions and capillary applicators 3. Describe the basic principle underlying all chromatographle processos. 4. Prodict the order of elution for the silica gel adsorption TLC separation of the mix- ture containing benzyl alcohol, benzaldehyde, and benzole acid using methylene chloride solvent. Explain. CH OH C-H OH benzyi alcohol benzaldehyde benzolo acid 5. The resolution caleulated for the TLC separation of a two-component mixture is determined to be equal to 2.0. Does this represent good separation or not? Explain. 6. When should a mixed-solvent system be used for TLC? Explain. 7, Is the order of elution of the components the same for TLC as for column chro- matography? 8. Explain how the various fractions can be analyzed from a gravity column. 9. What chromatographic technique would be useful: to determine whether a nonvolatile compound is pure? b. a. to separate a mixture of two nonvolatile solids? to determine whether a reaction is complete? c. 10. Caffeine absorbs UV light. Describe how to determine if a cup of coffee is caf- feinatod or decaffeinated using HPLC. Technique L: Polarimetry Optical activity is a physical property of chiral molecules. Chiral molecules lack planes of symmetey and mav exist as two or more stereoisomers. Stereolsomers that otate theExplanation / Answer
ANSWER 4:
The mobile phase used is organic (methylene chloride) and the silica gel is the stationary phase. Based on the eluting power (polarity) of the alcohol, aldehyde and acid that is present in the column as benzyl alcohol, benzaldehyde and benzoic acid, since the polarity of the acid is the most, followed by the alcohol and lastly the aldehyde.
Benzoic acid separates first, followed by benzyl alcohol and lastly benzaldehyde.
ANSWER 7:
Yes, the order of elution would be the same even for column chromatography. The Benzoic acid elutes out first, followed by benzyl alcohol and lastly benzaldehyde.
ANSWER 8:
In the case of a gravity column, the elution would be based on the molecular weights of the samples. The one with the largest molecular weight would exit the column first and so on.
ANSWER 9:
a) to deretermine purity of a non voltile compund, Thin layer chromatography (TLC) would be used. If the compound found is pure, only a single blue spot would be visible on the plate.
b) To separate a mixture of 2 non volatile solids, column chromatography would be used as they would have different elution times when the solid mixture is dissolved in a suitable solvent and poured into the column, which is then further eluted using a mobile phase.
c) to determine whether a reaction is complete, TLC would be used again. This is done by placind a spot of the reactants used and the product formed on the starting point of the TLC plate and placing the plate in the mobile phase which would carry the compounds to the end point. If the product'c Rf value matches the actual theoretical value, it indicates that the product is formed.
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