Question

Lab Day 8: Chromatography Prelab Questions 1) The basic food colors you can buy are red, blue areen, and yellow. Think about what you know about colors and predict which of these might be a single colored compound and which ones might contain more than one. write down your prediction. If you have the colors listed and want a purple color, what would you do? 2) Put the following chromatography solvents in order of polarity as a chromatography solvent: acetone, n-propanol, water, hexane, diethyl ether, methanol. Explain your order based on what you have learned in CHEM 120. 3) You will be doing chromatography with a mixture of n-propanol and water. Would it make sense to add hexane to this mixture to try and make it work better? Explain. 4) Two cars full of people took a day trip. Car A had a lot of little kids and stopped at lots of rest stops and gas stations to give them a break. Car B had just adults in it, and only stopped once. Of course Car B got to the destination first. Explain how this in an analogy for the paper chromatography you are doing in this experiment.

Answer 1

1. Red, blue and yellow is single colour. Green can be mixture of blue and yellow. In order to get violet colour we can mix blue and red color.

2. Moving from least polar solvents to most polar solvents, we have hexane<diethyl ether<n-propanol<acetone~methanol<water

Polarity increased as their dipole moment increased.

3. If the column chromatography is to be done with a mixture of n-propanol and water that would mean that the compounds to be separeted are very polar. Whereas hexane is the least non-polar solvents, so adding hexane wouldn't make sense. If there is necessity to decrease the polarity of solvents, it's better to change the solvent system of n-propanol+water to a less polar solvent mixture.

4. Since the car carrying kids are stopping at more number of places, they reached the destination slower than the car carrying the adults who stopped only once. Similarly compounds which would bind more strongly to the paper (stationary phase) would rise up slowly (since they are stopping more) in the paper chromatography, than the compound which binds loosely to the paper(stationary phase).