Tech 707 and 708 Chromatography

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The percent recovery as shown below indicates the quality of the separation achieved in this experiment. We received a 58.3% recovery of ferrocene. This means that all of the initial ferrocene was not separated out. This could be due to a couple of reasons. Our percent recovery for the acetylferrocene was a much different result compared to the ferrocene. The percent recovery was 171.6% for the acetylferrocene. This can mean that a sample contains some of the ferrocene or it can be explained by some sources of error, mentioned below.

The TLC of ferrocene and acetylferrocene did not indicate any real cross contamination. This means that the samples separated out were not too mixed with one another. The Rƒ of each compound also makes sense. Since ferrocene is less polar it will have a higher Rƒ than acetylferrocene. Our collected compounds mimicked this. The calculated Rƒ for ferrocene is 0.910 and acetylferrocene is 0.651.

Percent Recovery:

= 0.583 x 100= 58.3% recovery of ferrocene[pic 5]

= 1.716 x 100= 171.6% recovery of acetylferrocene[pic 6]

Tech 708 TLC Sketch: See attached

Tech 707 Sketches

Test Solvents: See attached

Unknown Standards and Unknown Sketch: See attached

Sources of Error/Improvements:

Throughout this experiment there were many sources from which error could have arisen. One main error for our group was specifically seen in the percent recovery for the acetylferrocene. While separating out the acetylferrocene, there was crystals formation within the stem of the column. If the TBME was not squirted onto the end continuously, the stem would frost up and allow the solution to crystalize. In order to dislodge the crystals from the stem we used a paper clip. The paperclip was manipulated in order to insert it into the end of the column. This caused the column to break at the end. This breakage allowed for broken glass, which could have fallen into the beaker and altered the weight of the recovered product. This would explain why we received such a high percent recovery. Another source of error was the formation of an air bubble while separating the acetylferrocene. The formation of an air bubble would cause the bed to become irregular, which affects the movement of the compounds through the column. This could cause for the compounds not to separate out correctly allowing for impure samples to be recovered. On final source of error could be the contamination of the two compounds. If we did not separate out all of the ferrocene before adding the TBME, the acetylferrocene could contain some ferrocene as well. This could account for such a low and high percent recovery.

The results of the experiment could have been improved a few different ways. One improvement could be made upon the conditions in which the experiment was taking place. Had the environment been different, there may not have been any premature crystallization. The stem of the column fogged up immediately upon the absence of the TBME being squirted on it. Another improvement could be a better way to dislodge any crystal formation. The use of the paperclip was efficient, but also very difficult and rough on the column apparatus. Had there been a gentler way to remove the crystals, we could have eliminated some sources of error.

Post Lab Questions: See attached

References:

Tech 707, Ronald J. Wikholm, Brooks/Cole Cengage Learning, © 2004, Pages 69-77

Tech 708, Joe Jeffers, Brooks/Cole Cengage Learning, © 2004, Pages 78-90