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Chemical analysis (Chromotography (can be used to separate mixtures and…
Chemical analysis
Chromotography
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involves a stationary phase and a mobile phase - separation depends on the distribution of substances between the phases
the ration of the distance moved by a compound to the distance moved by solvent can be expressed as its Rf value
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different compounds have different Rf values in different solvents, which can be used to help identify the compounds - the 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
Pure substances
a pure substance is a singe element or compound, not mixed with any other substance
pure elements and compounds melt and boil at specific temperatures. melting point and boiling point data can be used to distinguish pure substances from mixtures
in everyday language, a pure substance can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state
Formulations
a mixture that has been designed as a useful product - many products are complex mixture in which each chemical has a particular purpose
made by mixing the components in carefully measured quantities to ensure that the product has the required properties
include fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
Test for hydrogen
uses burning splint held at the open end of a test tube of the gas - hydrogen burns rapidly with a pop sound
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Test for carbon dioxide
uses an aqueous solution of calcium hydroxide (lime water) - when carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy)
Test for chlorine
uses litmus paper - when damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white