Chemical Analysis

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  • Chemical Analysis
    • paper chromatography
      • mobile phase
        • where the molecules can move - always a liquid or gas
      • stationary phase
        • where the molecules cant move - solid or really thick liquid
      • an analytical method used to separate and identify the substances in a mixture
      • during the experiment the substances constantly move between the mobile and stationary phases - an equilibrium is formed between the phases
      • 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 its distributed between the two phases
      • 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 through the stationary phase, so long as all the components spend different amounts of time in the mobile phase
      • the number of spots may 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
      • in paper chromatography the stationary phase is the chromatography paper and the mobile phase is the solvent
      • molecules with a higher solubility in the solvent and that are less attracted to the paper will spend more time in the mobile phase - carried further up the paper
    • purity
      • a pure substance is something that only contains one compound or element throughout - not mixed with anything
      • a chemically pure substance will melt or boil at a specific temperature
      • you can tell the purity of a sample by measuring its melting or boiling point and comparing it with a pure substance
        • the closer your measured value is to the actual melting or boiling point, the purer your sample is
        • impurities in your sample will lower the melting point and increase the melting range of your substance
        • impurities will increase the boiling point and may result in your sample boiling at a range of temperatures
    • formulations
      • formulations are useful mixtures with a precise purpose that are made by following a formula
      • each component in a formulation is present in a measured quantity and contributes to the properties of the formula so that it meets its required function
      • really important in the pharmaceutical industry
      • can be found in cleaning products, fuels, cosmetics, fertilisers, metal alloys and food and drink
    • chromatography analysis
      • the result of chromatography analysis is called a chromatogram
      • an Rf value
        • Rf = distance travelled by substance(B) / distance travelled by solvent(A)
        • the further through the stationary phase a substance moves the larger the R value


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