Chapter 3- Separation and Purification

• A pure substance consists of a single element or compound.
• Pure substances have a constant and fixed boiling and melting point.
• Impurities cause variation in the melting and boiling points of the substance. Therefore, they can be used to determine if a substance is pure or not.
• Different purification techniques can be used to separate and purify substances.

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STEPS TAKEN DURING DISTILLATION:

1. Thermometer should be placed beside the sidearm of the distillation flask, not inside the liquid.
2. Water outlets should be positioned in the correct way with cold water in from the bottom and leaving from the top.
3. The condenser slopes downward so the pure solvent runs to the flask/beaker.
4. If the distillate is volatile, it has to be kept in a container containing ice so it doesn’t evaporate.

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Chromatography

• Different components separated using chromatography have distinct Rf values or Retention factors.

• Rf value is calculated by dividing the distance moved by the solute by the distance moved by the solvent.

• Rf values can be matched by the already known values to identify the component.

• Sometimes, the components are transparent such as amino acids. A locating agent (e.g. Ninhydrin) is sprayed on the chromatogram to make them visible.

  

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