Chemical Analysis

• A chemically pure substance...

  o only contains a single element or compound (not mixed with any other substance)

  o will only melt/boil at a specific temperature, impurities in a sample...

  ▪ decrease melting point & increase melting range of the substance

  ▪ increase boiling point & increasing boiling range of the substance

  o the closer you measured value is to the actually melting/boiling point, the purer the sample

  o e.g. oxygen gas, carbon dioxide gas
• • a formulation is...

  o a useful mixture with a particular purpose

  o made by mixing the components in carefully measured quantities to ensure that the product has the

  required properties
• • Chromatography can be used to separate mixtures & can give information to help identify substances

  o The result of a chromatography analysis is called a chromatogram

  • Chromatography involves 2 phases

  o Mobile – where the molecules can move (liquid or gas) – the solvent that moves through the paper

  o Stationary – where the molecules can’t move (solid or viscous liquid) – the paper
• Separation depends on the distribution of substances between the phases

  • The mobile phase moves through the stationary phase, anything dissolved in the mobile phase (solvent) moves

  with it

  • Each chemical in the mixture will be attracted to the stationary phase (paper) to a different extent

  o Chemicals strongly attracted to the stationary phase won’t move very far (less soluble in the solvent)

  o Chemicals weakly attracted to the stationary phase will move further up (highly soluble in the solvent)
• Rf = distance travelled by solute / distance traveled by solvent
• Hydrogen:

  Hold a burning splint at the open end of a test tube of gas

  Hydrogen burns rapidly with a squeaky pop

  (because hydrogen + oxygen → water)
• Oxygen:

  Inserting a glowing splint into a test tube of gas

  The splint relights
• Carbon dioxide:

  Bubble through carbon dioxide through lime water (calcium hydroxide)

  The limewater turns cloudy
• Chlorine:

  Put damp litmus paper into chlorine gas

  The litmus paper is bleached & turns white

  (may temporarily turn red as chlorine is acidic)
• Lithium - Crimson

  Sodium - Yellow

  Potassium - Lilac

  Calcium - Orange-red

  Copper - Green
• o Copper (II) – Cu2+ → Blue

  o Iron (II) – Fe2+ → Green

  o Iron (III) – Fe3+ → Brown

  o Calcium – Ca2+ → White

  o Magnesium – Mg2+ → White

  o Aluminium – Al3+ → White, then redissolves in excess sodium hydroxide to form a colourless solution
• • Carbonates (CO32-) react with dilute hydrochloric acid to produce carbon dioxide

  • So to test for carbonates you react the sample with dilute HCl then bubble any gas produced through limewater

  o if the limewater goes cloudy the gas produced was CO2, so the sample contains carbonate anions
• Halides (anion test)

  • Halides are the ions of group 7 elements

  • Add dilute nitric acid to remove any impurities, then add silver nitrate solution

  o chloride (Cl-) produces a white precipitate (Silver chloride)

  ▪ e.g. Ag+ + Cl- → AgCl

  o bromide (Br-) produces a cream precipitate (Silver bromide)

  o iodide (I-) produces a yellow precipitate (Silver iodide)
• Sulfates (anion test)

  • Sulfates (SO42-) react with barium chloride solution to produce a white precipitate

  o Ba2+ + SO42- → BaSO4

  • Before adding barium chloride, add dilute hydrochloric acid to remove any traces of carbonate ions (which

  would also produce a precipitate confusing the results)
• Instrumental methods

  • Elements and compounds can be detected and identifies using instrumental methods (tests that use machines)

  • Instrumental methods are accurate, sensitive (detect even the tiniest amounts of substances) and rapid
• • Flame emission spectroscopy is an instrumental method used to analyse metal cations in a solution

  • The sample is put into a flame and the light given out (due to excited elections transferring energy as light) is

  passed through a spectroscope which detects the different wavelengths of light

  • The line spectrum produced can be analysed to identify the metal ions contained and their solutions

  o each ion produces a different spectrum due to the different electron arrangements and charges which produce different wavelengths of light

  the intensity of the lines indicates the concentration
• Describe what you would see when bromine water is added to an unsaturated organic compound.

  Goes colourless from brown