explain why the cation samples are repeatedly spotted and dried on the chromatog
ID: 890794 • Letter: E
Question
explain why the cation samples are repeatedly spotted and dried on the chromatographic paper.The eluent is to be below the 1.5 cm line on the chromatographic paper. Describe the expected observation if the eluent were above the 1.5 line. Explain why the center of the band is used to calculate the Rf value for a cation rather than the leading edge of the band
Suppose two cations have the same Rf value. How might you resolve their presence in a mixture using paper chromatography explain why the cation samples are repeatedly spotted and dried on the chromatographic paper.
The eluent is to be below the 1.5 cm line on the chromatographic paper. Describe the expected observation if the eluent were above the 1.5 line. Explain why the center of the band is used to calculate the Rf value for a cation rather than the leading edge of the band
Suppose two cations have the same Rf value. How might you resolve their presence in a mixture using paper chromatography explain why the cation samples are repeatedly spotted and dried on the chromatographic paper.
The eluent is to be below the 1.5 cm line on the chromatographic paper. Describe the expected observation if the eluent were above the 1.5 line. Explain why the center of the band is used to calculate the Rf value for a cation rather than the leading edge of the band
Suppose two cations have the same Rf value. How might you resolve their presence in a mixture using paper chromatography
Explanation / Answer
In the paper chromatographic analysis of cations, the samples are spotted several times to get a good concentration of the cation for clear identification and confirmation of it before drying the paper.
The Rf value is measured as the distance travelled by the solute upon the distance travelled by the solvent. It is important to mark the positions of the solvent and the solute front to accurately measure and analyse the samples by chromatographic technique. If however, the solvent is allowed to run beyond the marked 1.5 cm line, it would be difficult to measure the distance the solute and the solvent has travelled from the marked origin which would eventually give inaccurate results for the separation. thus it is of upmost importance to pay attention when runing a chromatophaphic plate/paper to not overrun the solvent beyound the marked line.
Depending on the concentration of the cation in the sample and the number of times the sample is spotted on the paper (which varies everytime you run a paper chromatographic separation), one would get different sizes for the spots developed for the cations. Thus to compare consecutive samples of cations we compare the distance travelled by the cation from the origin upto the centre of the spot. This gives more accurate results as when the distance upto the edge of spot (size differs with each run) is measured for the cation spot.
Suppose we have two cations with the same Rf value, then to resolve their presence we would use two different staining reagents to identify the cations. We have to make sure that the staining agent used are selective for one cation over the other in reaction.
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