Chapter 12: Experimental Techniques and Chemical Analysis — Part 4

01 Methods of Separation

The choice of method depends on the physical properties of the substances involved:

• Filtration: Separates an insoluble solid from a liquid. The liquid passes through the pores of the filter paper as the filtrate, while the solid remains as the residue.
• Crystallisation: Separates a soluble salt from its solution. The solution is heated until saturated, then allowed to cool so crystals form.
• Simple Distillation: Separates a solvent from a solution (e.g., pure water from saltwater). It works because the solute has a much higher boiling point than the solvent.
• Fractional Distillation: Separates miscible liquids with different boiling points (e.g., ethanol and water, or crude oil). The mixture is heated, and the liquid with the lowest boiling point evaporates first, passes through a condenser, and is collected.
• Separating Gases: A mixture of gases can be cooled into a liquid and then separated using fractional distillation.

02 Assessing Purity

• Pure substances have sharp, specific melting and boiling points.
• Mixtures (impure substances) melt and boil over a range of temperatures.
• Purity is determined by how close the experimental values are to standard database values. For example, pure water must boil exactly at 100°C.