Chromatography
Chromatography: How can we separate a mixture?
Purpose
The chromatography lab is to understand how molecules with similar molecular properties can be separated with paper chromatography. These differences will be interpreted to see the distinction of separate chemical substances.
Pre Lab Questions
1. Explain capillary action as it pertains to water and paper.
Capillary action makes water draw up the paper. As paper absorbs water mixes with the solutions in the paper.
2. What is the Rf value in a chromatography experiment?
Rf = Distance travelled by the solute from the original line/distance travelled by the solvent from the original line
3. If a molecule has a high affinity for the stationary phase, how is the Rf value affected?
High affinity for the stationary phase affects the Rf value by lower Rf values.
4. If a molecule has high affinity for the mobile phase, how is the Rf value affected?
The Rf value will be higher
5. Imagine you are doing a chromatography experiment with a polar solvent and a molecule containing a carbonyl group. Would the Rf value be high or low? Explain.
The Rf value would be predicted as being low because it would tend to stick to the paper more.
6. Why must a pencil be used, instead of a pen or marker when marking chromatography plates?
A pencil is being used when parking chromatography plates because the ink could take part in reacting with the substance that it is placed in.
7. Why should latex gloves be worn when preparing chromatography plates?
Latex gloves should be worn to prevent contamination of the chromatogram
8. The sample fine thin-layer chromatography plate, shown below, was prepared by spotting methyl red at R, sudan III at S, and bromocresol green at G. A single drop of each was placed on M. The plate was put in the developing solution until the solvent front reached 10 cm. Estimate the retention factor of R,S, and G, by measuring to the middle of the spot.
Purpose
The chromatography lab is to understand how molecules with similar molecular properties can be separated with paper chromatography. These differences will be interpreted to see the distinction of separate chemical substances.
Pre Lab Questions
1. Explain capillary action as it pertains to water and paper.
Capillary action makes water draw up the paper. As paper absorbs water mixes with the solutions in the paper.
2. What is the Rf value in a chromatography experiment?
Rf = Distance travelled by the solute from the original line/distance travelled by the solvent from the original line
3. If a molecule has a high affinity for the stationary phase, how is the Rf value affected?
High affinity for the stationary phase affects the Rf value by lower Rf values.
4. If a molecule has high affinity for the mobile phase, how is the Rf value affected?
The Rf value will be higher
5. Imagine you are doing a chromatography experiment with a polar solvent and a molecule containing a carbonyl group. Would the Rf value be high or low? Explain.
The Rf value would be predicted as being low because it would tend to stick to the paper more.
6. Why must a pencil be used, instead of a pen or marker when marking chromatography plates?
A pencil is being used when parking chromatography plates because the ink could take part in reacting with the substance that it is placed in.
7. Why should latex gloves be worn when preparing chromatography plates?
Latex gloves should be worn to prevent contamination of the chromatogram
8. The sample fine thin-layer chromatography plate, shown below, was prepared by spotting methyl red at R, sudan III at S, and bromocresol green at G. A single drop of each was placed on M. The plate was put in the developing solution until the solvent front reached 10 cm. Estimate the retention factor of R,S, and G, by measuring to the middle of the spot.