Paper Chromatography
(Palko 1-8-05)
Purpose
You will use paper chromatography to separate inks and dyes into identifiable components. Principles of IM bonding will be utilized to explain the effects of various solvents.
Background
Chromatography is one of the most widely used separation tools in chemistry. It was invented by a Russian botanist, Mikhail Tswett, for use in the separation of plant pigments. Because each pigment had a unique color, components could be identified in this way and the process was named chromatography as a result as “chroma” means color. The technique has expanded greatly and does not require components to have a color just a means of identification that could accomplished a number of ways including using spectrophotometry.
All chromatographic methods involve two phases, a mobile phase which moves through or over a stationary phase. A mixture of solutes is initial present and dissolved in the mobile phase. As this solution travels through the stationary phase, the solute molecules or ions would all be moved along at the same rate if they all remained in the mobile phase. However, some may be attracted to the stationary phase and may be adsorbed or dissolved in that stationary phase. This attraction slows these solute particles. Since different molecules or ions will exhibit different degrees of “attracted-ness”, they will become separated and isolated.
In this exercise, we will use paper chromatography. In this method, the stationary phase is a sheet of paper that is composed primarily of cellulose. The paper is porous and therefore has a large surface area. This surface is covered with the hydroxy (OH) groups of the cellulose molecules and from water molecules that hydrogen bond to the cellulose. As a result it is very polar and will attract other polar molecules. So, more polar solutes will tend to adsorb to the paper and move more slowly than other less polar solutes. The polarity of the solvent...