chemistry topic 8

• what does a pure substance mean in chemistry?


  nothing has been added to it (natural state) e.g pure milk
• how many compounds or elements are in a pure substance?

  only one compound or element, not mixed with anything else
• what can tell you the purity of a substance?

  boiling or melting point of a substance
• a chemically pure substance will __ or ___ at a ___ tempreture

  melt or boil at a specific tempreture
• how do you test the purity of a samle?

  measure melting and boiling points of your substance than compare it to the pure substance bp∓ (can be foun in a data book)
• what determines the purity?

  the closer the value of melting&boiling points of your substance is to the pure sample, the purer it is. close to pure sample = purer
• what may lower the melting point and increase the melting range in a substance?


  impurities in your sample
• what can impurities do to boiling points of substances?

  increase boiling&melting point. may result in your sample boiling or melting at a range of temps
• what are formulations?


  mixtures with exact amounts of components
• what is the purpose of formulations?

  formulations are useful mixtures with a precise purpose
• how are formulations made?

  "made following a 'formula' (recipe). Each component is present in a measured quantity and contributes to properties of the formulation
• so it meets required function"
• what are 4 examples of formulations of paint?

  "pigment- gives paint colour. e.g titanium oxide used as pigment in white paints
• solvent- dissolve the other components and alter the viscosity
• binder(resin)- forms film that holds pigment in place after its been painted on
• additives-further change physical and chemical properties of the paint.
• depending on purpose of the paint, chemicals used and their amounts will be changed so the paint produced is right for the job
• why're formulations important in pharmaceutical industry?

  "chemists can make sure it delivers the drug to correct part of the body at right concentration and that its consumable and has a long
• shelf life."
• how many phases does chromatography use?

  two
• what is chromatography?

  analytical method to seperate substance in a mixture. then use it to identify the substance
• what are the 2 phases of chromatography?

  "mobile phase- molecules can move. Always a liquid or gas
• stationary phase- molecules cant move. Can be a solid or really thick liquid"
• what happens during a chromatography experiment?

  substances in smaple constantly move between mobile& stationary phases. an equilibrium is formed between the two
• what happens to chemicals that spend more time in the mobile phase?

  they'll move further in the stationary phase
• what determines how quick a chemical moves?

  depends how its 'distrubuted' between the two phases. whether it spends more time in the mobile or stationary phase
• what happens to the dissolved substance in the mobile phase?

  dissolved substance moves with the mobile phase through to the stationary phase
• what will happen to the components in the mixture?

  normally seperate through stationary phase, so long as all the components spend different amounts of time in the mobile phase
• why may the number of spots change?

  "distribution of the chemical will change depending on the solvent. pure substances only ever forms one spot in any solvent as there
• is ony one substance in the sample"
• what are the two things that decide how long the molecules spend in each phase?

  how soluble they are in water & how attracted they are to the paper
• what happens to molecules with a higher solubility in paper chromatography?

  it'll be less attracted to the paper, therefore it'll spend more time in the mobile phase, and they'll be carried further up the paper
• what is Rf value?

  "ratio between distanced travelled by dissolved substance (solute) and distance travelled by solvent. further through stationary phase
• a substance moves, the larger the Rf value."
• how do you calculate Rf?

  "Rf= distance travelled by substance (baseline to spot)
• distance travelled by solvent (baseline to solvent front)"
• why is chromatography used?

  see if certain substance is present in a mixture
• how can paper chromatography be used to see if theres a certain substance present?

  run pure sample and compare results to your sample. if Rf value & the spots match, substance may be present
• what is the Rf value dependent on?

  dependent on solvent, if solvent is changed then the Rf value for the substance will change
• you can test both the mixture and the reference in a number of different solvents, what can this allow?

  "if Rf value of reference compound match or one of the spots in the mixture in all solvents, then its likely the reference compound is