Help please! The Fundamentals of Chromatography Investigation Laboratory Questio

Question

Help please!

The Fundamentals of Chromatography Investigation Laboratory Questions 1. Why must the line of origin be drawn in pencil instead of pen on the chromatography strip? 2. Explain why an Rivalue is a dimensionless number. 3. Why is it better to allow the solvent front to move almost to the top of a paper strip rather than stopping it at the halfway point during development 4. A student calculated an Ri value to be 1.5. Explain why this is not possible. 5. What would happen if the sample spot on the strip was placed below the solvent level when placed in the test tube? 6. Why should the paper chromatography strip not touch the walls of the test tube during the analysis of a mixture? 7. Explain how the colors for strawberry, orange, and grape Kool-Aid® are made. 8. List the three known FD&C; dyes you examined in order of increasing polarity on your chromatography paper starting from the origin line.

Explanation / Answer

1. As pencil is made up of graphite, so when we mark the line with pencil it will not travel with solvent but when we use pen then its ink will also travel with the solvent used and we will get a complex picture of chromatographic strip and will not able to analyse it

2. As Rf value is the distance travelled by a compound divided by distance travelled by solvent. So, in both nominator and denominator same unit, which will cancel out each other. That is why Rf value is dimensionless.

3. Stopping it in half way will be in appropriate as we do not know how much a particular compund will travel in solvent. Travelling distance depend upon polarity of compound. If there are spot of compound which are non-polar or less polar then they will appear at top of chromatography strip and stopping it in half way does not let them to appear on the strip.

4. As Rf value is the distance travlled by compound divided by the distance travelled by solvent. And distance travelled by a solvent is maximum in any TLC chamber. So Rf value can not exceed then one for any compound.

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