Which developing solvent solution provided the best resolution of the indicator dye?  Which one was the worst?  Explain.

The distance traveled by all solvents was 5cm.

First is the solvent. G=Bromocresol green S=Sudan III R=methyl red M=mixture correlation. First number is distanced traveled by spot, second number is Rf value.

Acetone/ethanol (1:1) mixture G=5.0 cm-1.0 S=4.75 cm-0.95 R=4.0 cm 0.80 M=4.2 cm

Acetone/ethyl (1:1) mixture G=3.5 cm-0.70 S=4.75 cm-0.95 R=3.0 cm-0.60 M=2.5 cm

Acetone/hexane (3:2) mixture G=1.0 cm-0.20 S=4.5 cm-0.90 R=3.5 cm-0.70 M=3.0 cm

Ethyl acetate/ethyl (1:1) mixture G=4.0 cm-0.80 S=4.5 cm-0.90 R=3.7 cm-0.75 M=4.0 cm

Ethyl acetate/hexane (3:2) mixture G=0.5 cm-0.10 S=4.0 cm-0.80 R=2.5 cm-0.50 M=2.2 cm

Expert Answers

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This question involves a chromatography technique called TLC, or thin layer chromatography.  A glass plate coated with a thin layer of silica gel is spotted, or loaded, with a mixture of three dyes (bromocresol green, sudan III, and methyl red) at the bottom of the plate.  The plate is then placed in a glass chamber with a small amount of solvent in the bottom.  The solvent is absorbed by the silica gel and it runs up the plate from bottom to top.  It carries the dye mixture up the plate with it and the individual dyes separate since they travel through the silica gel at different speeds.  The amount of separation greatly depends on the exact solvent system used.  The best separation puts the most distance between the different dye spots when they are finished traveling up the plate.  The Rf factor is an easy way to measure this since it divides the distance traveled by the dye spot by the total distance traveled by the solvent front up the plate (so the values are fractions that range between 0 and 1).  The larger the difference in Rf factors, the more distance there is between the two dyes and the more effective the separation was.  So the final solvent system (ethyl acetate and hexane) appears to be the best resolution since the Rf factors are the most separated (0.1, 0.8, and 0.5).  The first solvent system (acetone and ethanol) appears to be the worst resolution since the Rf values are all close together (1.0, 0.95, and 0.8).

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