Paper Chromatography Lab Partner ______

Name ______Per_____ Paper Chromatography Lab Partner ______

Introduction Chromatography is a method of separating mixtures based on the properties of the substances being separated. Separation by chromatography generally requires two phases of matter - a stationary phase and a mobile phase. The stationary phase is usually a solid, in this case the paper, which allows some substances to pass through easily and holds others back. The mobile phase is either a gas or liquid (the water in this lab) which moves through the stationary phase, carrying the substances to be separated. Chromatography was invented in the early 1900s by Michael Tswett to separate plant pigments. Today many variations of chromatography are used to separate mixtures of substances so that they can be identified. The food industry uses gas chromatography to separate and identify the compounds that give foods their aromas. Some of the compounds discovered are then synthetically made in the laboratory and used for artificial flavors and fragrances. Gas-liquid chromatography is used for drug testing and for determining the percent of alcohol in a blood sample. One variation of chromatography that is becoming increasingly important is electrophoresis used for DNA fingerprinting. Forensic scientists use DNA fingerprinting to help identify people and solve crimes. In this laboratory experiment you will be using paper chromatography to separate several mixtures.

Pre-lab Questions 1) What is chromatography?

2) Name at least 3 properties that can be used to separate substances by chromatography.

Data 1) On a separate sheet of paper, create a data table that can be used to record and easily compare your qualitative observations for each of the substances that are being separated. Describe/diagram your results in your data table. (Reminder: all data tables should be drawn neatly using a ruler and must include a complete, descriptive title, and subtitles for columns and rows.) Include space to record observations for an unknown marker.

2) Re-draw and extend the sample data table below to record several quantitative observations for each of the

substances. Calculate the retention factor (Rf) values for each of the substances and record.

Rf = distance substance moved distance mobile phase moved

Table 2: ______Calculation of Retention Factor Values Additional Quantitative Obs.

Marker Color Distance Substance Distance Mobile Rf Value used Moved Phase Moved 1) a) b) c) (etc) 2) a) b) c) (etc) 3) (etc) Conclusions 1) How many different substances were found in each of the different pens? 2) The number/letter of your unknown is ______. What is its most likely identity?

Discussion 1) Define retention factor. Explain its usefulness.

2) Suggest some possible reasons for the occurrence of the qualitative observations you made (e.g. what reason(s) could explain the lack of color separation for one of the markers? etc...).

i) Observation: Explanation:

ii) Observation: Explanation:

iii) Observation: Explanation:

3) Some components of ink are minimally attracted to the stationary phase and very soluble in the solvent (mobile phase). Where are these components most likely to be located on the filter paper during chromatography?

4) Predict the results of forgetting to remove the chromatogram from the water in the petri dish until the next day.

5) How could this method be used to help identify an unlabeled marking pen?