i) the detection and identification of groups of atoms or ions which make up a substance.

ii) the compounds which these atoms and ions form.

iii) the relative amounts of the elements and/or compounds which are present in a particular substance.

The above are all used in industry for quality control.

Qualitative analysis - involves identification of a substance or the components of a substance ie what's in it?.

Quantitative analysis - involves the determination of the relative amounts of elements in a compound or components in a mixture ie how much of each chemical is present?.

Physical properties such as colour, solubility in water or melting temperature

Flame Tests is a form of qualitative analysis. It is used to identify the presence of certain metal ions since some metals produce particular colours when they are heated. The metallic elements present in a compound can be determined by inserting a sample of the compound into a non-luminous Bunsen burner flame. The metal is identified by comparing the flame colour with a list of characteristic colours.

In an atom electrons are located around the nucleus in regions called shells or energy levels. The shells closest to the nucleus have the lowest energies.

The first shell is called shell number 1 and has a symbol K

" 2^nd " " " " " 2 " " " " L

" 3^rd " " " " " 3 " " " " M

shell number (n) symbol maximum number of electrons

1 K 2

2 L 8

3 M 18

4 N 32

* note that the outermost shell cannot contain more than 8 electrons.

For every "allowed" electronic energy level in an atom, there corresponds a definite orbital for the electron to move in shells around the nucleus. * note each shell has a definite number of orbitals*.

Flame tests rely on the following: When atoms or ions are heated to high temperatures, one or more of their higher energy (outer-shell) electrons become excited (absorb energy). When the electrons become excited, they jump to a higher energy level (a shell further from the nucleus). The energy released in a Bunsen burner flame is enough to cause this to happen in a number of metal ions. Electrons that have been raised to a higher energy level are no longer in their stable state ie they are unstable and because of this they readily drop back to lower energy levels. In doing so they release (emit) the energy they previously absorbed in the form of photons (pockets) of light. The colour of light emitted depends on the energy of the photons. The metal is then identified by comparing the flame colour with a list of characteristic colours.

Energy from the flame promotes an Electron returns to a lower energy

electron to a higher energy level. level, in doing so emits light.

** The energy emitted by the excited electron is equal to the difference between the higher energy level and the lower energy level to which it returns. **

-Modification to flame testing.

The flame used here is hotter therefore sufficient is energy available to excite electrons in a wider range of elements. The light emitted is passed through a prism which causes it to be separated into a series of coloured lines - emission spectrum

(see fig 2.8 pg 12 "Chemistry Two")

The emission spectrum produced will be different for each element since each element has a different number of protons hence the attraction between the nucleus and electrons will vary for each element therefore the emission spectrum is characteristic of a particular element.

Limitation- only a few elements are excited even by the hottest flame.

Chromatography is a technique used for separating the various components of a mixture by selective removal of these components from a moving fluid. Chromatography is used mainly for mixtures of organic compounds. It is especially used in the areas of quality control and testing for the presence of particular compounds. It is also used for detecting impurities in food stuffs and pharmaceuticals, drugs present in blood, hydrocarbons in oils, identifying and measuring environmental pollutants, pesticides in water and soil and in forensic science.

Chromatography is based on the selective separation of different chemical substances from a moving gas or liquid stream (mobile phase) by a stationary adsorbing material. Adsorption is the formation of a layer of substance to the surface of a solid or liquid.

The mobile phase carries the substance/s being analysed and is always either a gas or a liquid.

The stationary phase takes up or adsorbs the separating components, this remains fixed hence called the stationary phase.

In general the mobile phase sweeps the components in the sample being tested over the stationary phase where they undergo a continual process of adsorption onto the stationary phase followed by desorption back into the mobile phase. The rate of movement of each component depends on how strongly it is attracted (adsorbed) on to the stationary phase and how readily it dissolves in the mobile phase. Strongly bound substances hardly move at all while a very weakly bound substance may move at almost the same speed as the solvent.

Stationary phase is a high quality adsorbent paper.

Mobile phase is a solvent.

A drop or spot of the sample to be tested is placed on the paper (origin) just above the surface of a solvent into which the paper is dipping. As the solvent moves up the paper the components of the spot will be separated according to their relative strengths of attraction for the paper fibres and the solvent.

Stationary phase is a thin layer of some finely divided solid such as silica gel or aluminium oxide (alumina) spread on a rigid plate (either glass or plastic).

Mobile phase is a solvent.

In operation paper and thin-layer chromatography are similar in that a drop of solution containing the substance to be separated is placed on the stationary phase which is then placed in contact with a suitable solvent. The solvent (mobile phase) then creeps slowly along the stationary phase.

For both paper and thin-layer chromatography components in a mixture can be identified by the Rf value. The Rf value is the ratio of the distance moved by a particular component from the origin to the distance moved by the solvent from the origin.

Rf = distance moved by a particular component from the origin

distance moved by the solvent from the origin

Rf is always less than one.

The most strongly adsorbed component moves the shortest distance and hence has the lowest Rf value.

see figure 2.12 pg 14 "Chemistry Two"

Stationary phase is a solid that is packed into a glass column.

Mobile phase is a solvent.

The sample to be analysed is applied to the top of the column and the solvent is dropped from a reservoir into the top of the column. A tap at the bottom of the column is opened to allow the solvent to leave the column at the same rate it is entered.