1. Chemical Analysis
Chemists play an important role in society by monitoring our environment to ensure that it remains healthy and safe and that pollution is tackled as it arises.
A variety of methods exist which enable chemists to monitor the environment both qualitatively and quantitatively, such as acid/base titration, precipitation, flame testing.
Titrations
Remember the titration calculation in unit 1 – Pa x Va x Ca = Pb x Vb x Cb (where P is the number of H+ or OH- in the acid/alkali, C is the concentration and V is the volume)
The concentration of an acid or alkali can be calculated by carrying out an experiment called a titration.
During a titration experiment ROUGH results should NEVER be used in calculations.
The average volume used in a titration is calculated by adding together the two values within 0.2cm3 of each other and dividing by two.
An indicator is used to the end point of a titration (usually via a colour change.)
Chromatography
Chromatography can be used to separate mixtures of coloured compounds. Mixtures that are suitable for separation by chromatography include inks, dyes and colouring agents in food.
Precipitation
A precipitation reaction occurs when two solutions react together to produce another solution and a solid. We can use page 8 of the data book to work out whether or not a compound is soluble or insoluble. The solid is classed as an insoluble salt (precipitate).
e.g. Lead (II) Nitrate + Sodium Iodide Lead (II) Iodide + Sodium Nitrate
Pb(NO3)2 (aq) NaI2 (aq) PbI2 (s) NaNO3 (aq)
This precipitation reaction is also a displacement reaction (i.e. the metals swap places)