Chemical Analysis

12.1 Substances and mixtures

• Pure in advertisement means nothing has been added and it is in its natural state
• A pure substance in chemistry is one made up of just one substance and it's either a compound or element
• The m.p.t and b.p.t of an element/compound is it's fixed point
• Pure elements/compounds melt/boil at specific temps, and these fixed points can be used to identify them using databases
• B.pt and m.pts of mixtures range and it changes state over a range of temps
• Impurities lower the m.p.t of a substance and raise its b.p.t. The range depends on the amount of impurities
• The purer the substance the narrower the m.p.t range
• Formulations are useful mixtures made up of definite proportions, designed to give a product the best propertie possible to carry out a function, e.g. alloys, fertilisers, pesticides, cosmetics, food products
  • e.g = paint. It has:
  • a pigment, to provide colour
  • a binder, to help the paint attach to an object and to form a protective film when dry
  • a solvent, to help the pigment and binder spread well by thinning them out

• e.g = washing up liquid. It has:
• a surfactant, the actual detergent
• water, to thin out the mixture 
• colouring and fragrance additives, improve the appeal of product
• rinse agent, help water drain off crockery

12.2 Analysing chromatograms

Chromotography always has a mobile and stationary phase. The mobile phase moves the stationary phase, carrying the components of the mixture with it. The components have different attractions to the mobile/stationary phases. A substance with stronger forces of attraction between itself and the mobile phase than between itself and the stationary phase will be carried a further distance in a given time. A substance w/ a stronger force of attraction to the stationary phase will not travel as far. In paper chromotography the mobile phase is the solvent and stationary phase is the paper.

Rf = distance moved by substance…