Topic 8,9,10

Página 1

Topic 8 - Purity and formulations

In chemistry, a pure substance is something that only contains on element or compound.

A chemically pure substance will melt or boil at a specific temperature.

You can test the purity of substances by comparing the melting or boiling point of it to a pure substance. The closer the substance is to the actual melting or boiling point the pure the substance is.

Impurities will lower the melting point and increase the melting range. Impurities will also increase the boiling point and can result in a substance to boil at a range of temperatures.

Formulations are useful mixtures with a precise purpose that are made by following a formula. Each component is presented as a measured quantity and contribute to the properties so, that the formulation meets it`s required function.

In everyday life formulations, in be found in cleaning products, fuels, cosmetics, fertilisers, metal alloys, food and drink.

Paper Chromatograhy

Chromatography is an analytical method used to separate the substances in a mixture. All types of chromatography have 2 phases:

1) A mobile Phase - where the molecules can move. This is always a liquid or a gas.

2) A stationary phase - where the molecules can`t move. This can be a solid or a really thick liquid.

The mobile phase moves through the stationary phase, and anything dissolved in the mobile phase moves with it. How quickly a chemical moves depends on how it is distributed between the 2 phases. (Whether it spends more time the mobile or stationary phase.)

The chemicals that spend more time in the mobile phase than the stationary phase will move further through the stationary phase.

The components in a mixture will normally separate during the stationary phase, so long as all the components spend different amounts of time during the mobile phase. The number of spots can change in different solvents as the distribution of the chemical will change depending on the solvent. A pure substance will only ever form one spot in any solvent as there is only one substance in the sample.

During paper chromatography, the stationary phase is the chromatography paper and the mobile phase is the solvent. The amount of time the molecules spend in each phase depends on two things:

1) How soluble they are in the solvent.

2) How attracted they are to the paper.

Molecules with a higher solubility in the solvent, and which are less attracted to the paper, will spend more times in the mobile phase - and they`ll be carried further up the paper.

The result of chromatography analysis is called a chromatogram.

Página 2

Página 3