Chemical Analysis

• purity 


  a substance being pure usually means nothing has been added to it, so it is in its natural state

  in chemistry a pure substance is something that only contains one compound or element throughout, not mixed with anything else
• the boiling or melting point tells you how pure a substance is


  a chemically pure substance will melt or boil at a specific temperature

  a purity of a substance can be measured by measuring its melting or boiling point and comparing it with the melting or boiling point of the pure substance. the closer the value is, the purer it is

  impurities will lower the melting point and increase the melting range of a substance. impurities will also increase the boiling point
• formulations are useful mixtures with a precise purpose 


  they are made by following a formula. each component in a formulation is present in a measured quantity and contributes to the properties of the formulation so that it meets its required function

  they are important in the pharmaceutical industry and cleaning products information in the packaging reveals the formulation
• tests for common gases

  chlorine- litmus paper

  oxygen- glowing splint

  carbon dioxide- limewater

  hydrogen- squeaky pop
• test for chlorine 


  chlorine bleaches damp litmus paper, turning it white
• test for oxygen 


  if a glowing splint is put inside a test tube containing oxygen, the oxygen will relight the glowing splint
• test for carbon dioxide 


  bubbling carbon dioxide through an aqueous solution of calcium hydroxide (limewater) causes the solution to turn cloudy
• test for hydrogen 


  if a burning splint is held at the open end of a test tube containing hydrogen, a squeaky pop can be heard
• chromatography uses two phases

  chromatography is an analytical method used to separate the substances in a mixture

  a mobile phase- where the molecules can move-liquid/gas

  a stationary phase-where the molecules can't move-solid or really thick liquid
• chromatography


  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 whether it spends more times spent in the mobile phase or the stationary phase

  the chemicals that spend more time in the mobile phase will move further through the stationary phase
• in chromatography 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
• a pure substance will only ever form in one spot in any solvent since there is only one substance in the sample
• paper chromatography


  in paper chromatography the stationary phase is the chromatography paper and the mobile phase is the solvent
• the amount of time the molecules spend in each phase depends on

  how soluble they are in the solvent

  how attracted they are to the paper
• molecules with a higher solubility in the solvent which are less attracted to the paper will


  spend more time in the mobile phase and will be carried further up the paper
• the result of a chromatography analysis is called a chromatogram 


  an r value is the ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent
• Rf


  distance travelled by substance (baseline to centre)/

  distance travelled by solvent (A)
• the further through the stationary phase a substance moves, the larger the Rf value


  often carried out to see if a certain substance is present in a mixture, a pure substance of the mixture must be run alongside the unknown mixture. If the R values match, the substance may be present
• The Rf value is affected by the solvent 


  the Rf value of a substance is dependent on the solvent you use- if you change the solvent, the R value for the substance will change
• flame emission spectroscopy


  a sample is placed in a flame. as the ions heat up, their electrons move to a higher energy level. when electrons drop back to their original energy levels, they release energy as light

  the light passes through a spectroscope, which can detect different wavelengths of light to produce a line spectrum.
• the combination of wavelengths emitted by an ion depends on its charge and electron arrangement 


  no two ions have the same charge and the same electron arrangement

  different ions emit different wavelengths of light

  so each ion produces a different pattern of wavelengths, and has a different line spectrum

  the intensity of the spectrum indicates the concentration of that ion in solution- line spectra can identify ions in a solution and calculate their concentration
• flame emission spectroscopy works in mixtures

  this makes it more useful than flame tests, which only work for substances that contain a single metal ion
• machines can analyse unknown substances

  chemists often use instrumental analysis such as flame emission spectroscopy instead of conducting manual tests
• advantages of using machines

  very sensitive-detect even the tiniest amount

  very fast- tests can be automated

  very accurate