chemical analysis

• a pure substance is something that only contains one compound or element throughout
• you can test the purity of a sample by measuring its melting or boiling point and comparing it with the melting or boiling point of the pure substance
• formulations are useful mixtures with a precise purpose that are made by following a formula
• each component in a formulation is presented in a measured quantity and contributes to the overall properties of the product
• by altering the formulation of a pill, chemists can make sure it delivers the drug to the correct part of the body at the right concentration
• chromatography uses two phases
• what is the mobile phase?

  where the molecules can move
• what is the stationary phase?

  where the molecules can't move
• the chemicals that spend more time in the mobile phase than the stationary phase will move further
• during 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 what two things?


  how attracted they are to the paper

  how soluble they are in the solvent
• how do you calculate the Rf value for each chemical?

  Distance travelled by substance

  --------------------------------

  distance travelled by solvent
• test for chlorine:

  chlorine bleaches damp litmus paper
• test for oxygen:

  re-lights a glowing splint
• test for carbon dioxide:

  bubbling carbon dioxide through limewater causes the solution to turn cloudy
• test for hydrogen:

  if you hold a lit splint at the open end of a test tube containing hydrogen you will hear a squeaky pop
• dilute acids can help detect carbonate:

  use a dropping pipette to add a couple of drops of dilute hydrochloric acid followed by a couple of drops of barium chloride solution to a test tube containing the solution. If sulfate ions are present, a white precipitate of barium sulfate will form
• test for halides with nitric acid and silver nitrate:

  to identify a halide ion, add a couple of drops of dilute nitric acid, followed by a couple of drops of silver nitrate solution
• what colour flame do lithium ions burn with?

  crimson
• what colour flame do sodium ions burn with?

  yellow
• what colour flame do potassium ions burn with?

  lilac
• what colour flame do calcium ions burn with?

  orange-red
• what colour flame do copper ions burn with?

  green
• what colour precipitate does calcium form with NaOH?

  white
• what colour precipitate does copper(II) form with NaOH?

  blue
• what colour precipitate does iron(II) form with NaOH?

  green
• what colour precipitate does iron(III) form with NaOH?

  brown
• what colour precipitate does aluminium form with NaOH?

  white at first, but the redissolves in excess NaOH to form a colourless solution
• what colour precipitate does magnesium form with NaOH?

  white
• during a flame emission spectroscopy a sample is placed in a flame, as the ions heat up their electrons become excited. When the electrons drop back to their original energy levels, they transfer energy as light