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Edexcel IGCSE Chemistry Topic 1: Principles of chemistry Elements, compounds and mixtures Notes

Edexcel IGCSE Chemistry Topic 1: Principles of chemistryrsbstudy.com/resources/Science/Chemistry/Single... · Edexcel IGCSE Chemistry Topic 1: Principles of chemistry Elements, compounds

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  • Edexcel IGCSE Chemistry

    Topic 1: Principles of chemistryElements, compounds and mixtures


  • 1.8 understand how to classify a substance asan element, compound ormixture

    ● Element =substance made from only one type of atom

    ● Compound = substance made from two or more elementsthat have reactedchemically with each other

    ● Amixture:

    o Consistsof 2 or more elementsor compoundsnot chemically combined


    o Chemical propertiesof each substance in the mixture are unchanged

    1.9 understand that a pure substance hasa fixed melting and boiling point,

    but that a mixture may melt or boil over a range of temperatures

    ● Apure substance =a single element or compound, not mixed with any othersubstance

    ● In everyday language, a pure substance = substance that hashad nothing addedto it, so it isunadulterated and in itsnatural state, e.g. pure milk

    ● Pure substancesmelt and boil at specific temperatureso Thismeltingand boiling pointsdata can be used to distinguish pure

    substances from mixtures(which melt over a range of temperaturesdueto them consisting of 2 or more elementsor compounds)

    1.10 describe these experimental techniquesfor the separation of mixtures:simple distillation, fractional distillation, filtration, crystallisation, paperchromatography

    ● Simple distillationo Used to separate a pure liquid from a mixture of liquids

    ▪ Workswhen the liquidshave different boiling points▪ Commonly used to separate ethanol from water▪ (Taking the example of ethanol…) ethanol hasa lower bp than

    water so it evaporatesfirst. The ethanol vapour is then cooled andcondensed inside the condenser to form a pure liquid.

    ▪ Sequence of events in distillation isas follows: heating ->evaporating -> cooling ->condensing

    ● Fractional distillationo The oil isheated in the fractionatingcolumn and the oil evaporatesand

    condensesat a number of different temperatures.o The many hydrocarbonsin crude oil can be separated into fractionseach

    of which containsmoleculeswith a similar number of carbon atoms

  • o The fractionatingcolumn workscontinuously, heated crude oil ispiped inat the bottom. The vaporised oil risesup the column and the variousfractionsare constantly tapped off at the different levelswhere theycondense.

    o The fractionscan be processed to produce fuelsand feedstock for thepetrochemical industry.

    ● Filtrationo If you have produced e.g. a precipitate (which isan insoluble salt), you

    would want to separate the salt/precipitate from the salt solution.▪ You would do thisby filtering the solution, leaving behind the

    precipitate● Crystallisation

    o If you were to have produced a soluble salt and you wanted to separatethissalt from the solution that it wasdissolved in

    ▪ You would first warm the solution in an open container, allowingthe solvent to evaporate, leavinga saturated solution

    ▪ Allow thissolution to cool▪ The solid will come out of the solution and crystalswill start to

    grow, these can then be collected and allowed to dry● Paper chromatography

    o Chromatography…▪ Used to separate mixturesand give information to help identify

    substances▪ Involvesa stationary phase and a mobile phase▪ Separation dependson the distribution of substancesbetween

    the phases

    Paper Chromatography Analytical technique separating compounds by theirrelative speeds in a solvent as it spreads through paper.

    The more soluble a substance is, the further up the paperit travels.

    Separatesdifferent pigments in a coloured substance.

    Pigment Solid, coloured substance

    1.11 understand how a chromatogram provides information about the

    composition of a mixture● see 1.10- separatesmixture into individual components, so revealsnumber of

    components in mixture and these componentscan be identified usingRf values● Compounds in a mixture may separate into different spotsdependingon the

    solvent but a pure compound will produce a single spot in all solvents

  • 1.12 understand how to use the calculation of Rf valuesto identify the

    componentsof a mixture● Rf value = distance moved by substance / distance moved by solvent ( /

    representsa dividingsign)▪ Different compoundshave different Rf values in different

    solvents, which can be used to help identify the compounds

    1.13 practical: investigate paper chromatography using inks/ food