Purity, formulations and chromatography

• A pure substance is a single element or compound, not mixed with any other substance.
• Pure substances melt and boil at specific temperatures, which can be used to distinguish them from mixtures.
• In everyday language, a pure substance is a substance that has had nothing added to it, so it is unadulterated and in its natural state, for example, pure milk.
• A formulation is a mixture that has been designed as a useful product.
• Many products are complex mixtures in which each chemical has a particular purpose.
• Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.
• Examples of formulations include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
• Chromatography is used to separate mixtures and give information to help identify substances.
• Chromatography involves a stationary phase and a mobile phase, and separation depends on the distribution of substances between the phases.
• Rf value is the distance moved by a substance divided by the distance moved by the solvent.
• Different compounds have different Rf values in different solvents, which can be used to help identify the compounds.
• Compounds in a mixture may separate into different spots depending on the solvent but a pure compound will produce a single spot in all solvents.
• Paper chromatography is an analytical technique separating compounds by their relative speeds in a solvent as it spreads through paper.
• The more soluble a substance is, the further up the paper it travels.
• Paper chromatography separates different pigments in a coloured substance.