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Solution concentration
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Moles per litre (molarity) mol $L^{-1}$: $c = \frac{n}{v}$
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c is the concentration of solute in moles per litre (mol L-1)
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n is the amount of solute in moles (mol)
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V is the volume of solution (solvent + solute) in litres (L)
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Grams per litre g L-1: $c_{gL}^{-1} = \frac{m}{v}$
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$c_{gL}^{-1}$ is the concentration of solute in grams per litre (g L-1)
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m is the mass of solute in grams (g)
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V is the volume of solvent (solvent + solute) in litres (L)
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Parts per million (by pass) ppm: $c_{ppm} = \frac{m_{s}\times 10^{6}}{m_t}$
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cppm is the concentration of solute in parts per million by mass (ppm)
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ms is the mass of solute in grams (g)
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mt is the mass of solution (solvent + solute) in grams (g)
Chromatography can be used as a separation technique, or as a technique to identify components of a mixture for further use or for analysis.
Key requirement is that it contains a stationary phase and mobile phase.
Stationary phase:
- The phase that does not move. Compounds in the mixture are attracted to it (adsorbed) and slowed down. Either a solid or a liquid.
Mobile phase:
- The phase that moves. The more soluble compounds in the mixture are carried faster as the mobile phase moves. Either a liquid or a gas.
Paper chromatography:
- Is used to separate mixtures, especially dyes or pigments.
- We put the mixture on a line of origin
- Note that we do not place the line of origin within the solvent, as the mixture would simply dissolve in the solvent and not move up the stationary phase.
- Dots of single dyes are placed alongside a dot of the unknown mixture.
- The solvent is drawn up the paper by capillary action.
- As the solvent moves up the paper, the pattern of the single dyes can be compared to that of the mixture's pattern.
Thin layer chromatography:
- All chromatography involves a stationary and mobile phase.
- In TLC, the stationary phase is a layer of silica gel fixed onto a glass plate.
- The mobile phase is a solvent which travels up the plate, carrying the substances.
- Has the same principles as paper chromatography.
- TLC involves a stable silica gel, but paper in paper chromatography is flexible and might affect results of chromatography. In TLC, the glass plate does not bend, and thus you will have better results.
- Capillary action still draws the solvent up the matrix; however while the molecules in paper chromatography are separated based on mass, in TLC, separation often depends upon solubility or charge, due to the interaction of solute and matrix.
- A dry sample is placed in the silica gel matrix. As the solvent front moves up the gel, it dissolves the sample and caries it up the matrix with it.
- Some of the particles in the sample stick more strongly to he silica gel than others, so they lag behind the solvent
- Eventually the different substances in the sample separate out, with similar molecules travelling a similar distance.
