Topic 8 Chemical analysis

• Pure substance


  Made up of only one compound or element throughout, it is not mixed with anything else.
• Testing purity


  Measuring the melting or boiling point and comparing with the melting or boiling point of the pure substance from a data book.
• Chemically pure substance


  Will melt or boil at a specific fixed temperature.
• Impurities

  Will lower the melting point and increase the melting range of your substance

  Impurities will also increase the boiling point and may result in your sample boiling at a range of temperatures.
• Formulations


  Useful mixtures with a precise purpose, made by following a formula.

  Each component of the formulation is present in a measured quantity, allowing them to contribute to the properties of the formula and meet its required function.
• Chemicals in a formulation can be altered to produce a formulation which is right for it's specific job.
• Formulations in the Pharmaceutical industry 


  By altering the formulation of a pill the chemist can ensure it

  Delivers the drug to the correct part of the body

  At the right concentration

  Consumable

  Has a long enough shelf life.
• Formulations in everyday life

  Cleaning products

  Fuels

  Cosmetics

  Fertilisers

  Metal alloys

  Food and drink
• Paper chromatography


  Analytical method used to separate the substances in a mixture.
• Mobile phase

  Where the molecules can move

  Always liquid or gas

  The solvent (eg ethanol or water)
• Stationary phase


  Where the molecules can't move

  Solid or thick liquid

  The chromatography paper
• Phases


  During chromatography, substances in the sample constantly move between the mobile and stationary

  An equilibrium is formed between the two phases.
• The mobile phase


  The mobile phase moves through the stationary phase, anything dissolved in the mobile phase moves with it.
• Solubility

  The more soluble a molecule within a solvent and the less attracted to the chromatography paper, the molecule/substance will spend more time in the mobile phase and will be carried further up the paper
• Pure compound

  A pure compound will produce a single spot in all solvents
• Mixture/ impure substance


  The compounds in a mixture will usually separate through the stationary phase into different spots, as long as all the components spend different amounts of time in the mobile phase.
• Calculating RF value

  The further through the stationary phase a substance moves the higher the Rf value.
• Rf value


  Rf value = distance travelled by substance/distance travelled by solvent.
• Testing for a substance in a mixture

  Run a reference of a pure sample of that substance alongside the unknown mixture, if the Rf values match, in ALL SOLVENTS, the reference compound is likely to be present.

  If the Rf values are only the same in SOME SOLVENTS then the reference compound is not present within the mixture.
• Rf value


  Dependent upon the solvent, changes in different solvents as some substances have different solubility in different solvents.
• Testing for gases (Chlorine)

  Bleaches damp litmus paper turning it white

  (May initially turn red because a solution of chlorine is acidic)
• Testing for gases (Oxygen)


  Putting a glowing splint in a test tube containing oxygen causes the glowing splint to relight.
• Testing for gases (Carbon dioxide)

  Bubbling carbon dioxide through an aqueous solution of calcium hydroxide (Limewater) causes the solution to turn cloudy.
• Testing for gases (Hydrogen)


  Holding a lit splint at the open end of a test tube containing hydrogen gas, produces a squeaky pop.

  From hydrogen burning quickly with the oxygen in the air to form H20
• Testing for Anions (Negatively charged ions) CARBONATES

  Carbonates are tested for by adding dilute HCL to the solution, then connecting the test tube to a test tube of limewater. If carbonate ions are present CO2 will be released, turning the limewater cloudy as it bubbles through.
• Test for Carbonate ions equation

  Na2CO3 + 2HCL = CO2 + 2NACl + H2O
• Sulfate (Anion test)


  Adding dilute HCl to remove any traces of carbonate ions which would also react to produce a precipitate, confusing the results. (impurities)

  Followed by a few drops of barium chloride solution to a test tube containing the mystery solution.

  If sulfate ions are present a white precipitate of barium sulfate will form.
• Test for Sulfate ions equation

  Ba 2+ + SO4 2- = BaSO4
• Halides (Anion test)


  Halides are tested for by adding dilute Nitric acid to remove any impurities. Followed by adding silver nitrate solution.

  The halides are Cl- Br- I-
• Chloride anion test

  Ag+ + Cl- =AgCl

  A chloride ion gives a white precipitate of silver chloride.
• Bromide anion test

  Ag+ + Br- = AgBr

  Bromide ions give a cream precipitate of silver bromide
• Iodide anion test

  Ag+ + I- = AgI

  Iodide ions give a yellow precipitate of silver iodide
• Flame tests for Cations Lithium Li+

  Burn with a Crimson flame
• Flame test for Cations Sodium Na+

  Burn with a yellow flame
• Flame test for Cations Potassium K+


  Burns with a crimson flame
• Flame test for Cations Test for Calcium Ca 2+

  Burn with an orange-red flame.
• Flame test for cations Copper Cu 2+

  Burn with a green flame
• Flame emission spectroscopy

  Can identify different ions in a mixture. Unlike flame tests which can only work for substances containing a single metal ion.
• Line spectrum


  A sample is placed in a flame, causing the ions to heat up and transfer energy as light as the electrons drop back to their original energy levels.

  The light passes through a spectroscope, which can detect different wavelengths of light to produce a line spectrum.
• Wavelengths

  The combination of wavelengths emitted by an ion depends on its charge and electron arrangement

  Different ions emit different wavelengths and has a different line spectrum.