chemistry analysis

• chemical analysis


  about instruments and methods that we use to:

  • separate
  • identify
  • quantify

  different substences
• purity


  only one type of compound or element - eg pure water

  melt and boil at specific temperatures - eg water = 100'C - physical test opposed to reacting with another chemical (chemical test)

  impure substance - doesn't have a specific melting and boiling point - rand of temperatures - low melting point but high boiling point
• formulations


  mixture that have been prepared using specific formula's - contain precise measurement of different components

  have a particular function

  examples - fuels, cosmetics, food, paint, medicine, alloys, fertilisers, drinks, cleaning agents

  different components will always be present in the same proportions

  each component may contribute a different property
• chromatography


  general analytical technique to separate substances in a mixture - pure substances won't separate

  different types - paper - separates dyes in ink
• chromatography


  lid - stops the solvent evaporating

  baseline = pencil - doesn't dissolve in the solvent - don't submerge into the solvent

  A) lid

  B) filter paper

  C) solvent - water/ethanol

  D) pencil baseline

  E) ink

  
• Chromatogram


  the pattern of spots that are left

  each die in the ink will dissolve in the water at different rates due to their different properties - some will be more attracted to the paper (move slower) some will be more attracted to the solvent (more quicker)

  if a substance isn't soluble they won't dissolve off the pencil baseline
• mobile phase 


  substance that molecules move in

  solvent or gas
• stationary phase


  substance molecules can't move in

  paper
• during chromatography, different chemicals in the sample will move change between the stationary and the mobile phases - dissolve in solvent, move, stick to the paper - over and over again - how long they spend in each phase determines how far they move up the paper;

  • more soluble - longer in the mobile phase = fast
  • less soluble - longer in the stationary phase = slow
• Rf values


  how far it travels depends on the properties of substance and how long the experiment is

  measure how far the substance move - compare to a data book

  can change if different mobile/stationary phases are used

  always less then 1

  $Rf=$$\frac{dis\tan ce\ travelled\ by\ subs\tan ce}{distnce\ travelled\ by\ solvent}$
• test for gas - chlorine


  test tube full of sample gas

  take a piece of damp, blue litmus paper and place it in the test tube

  paper turns red then white - bleached

  this is because the Cl dissolves in the water on the damp paper to form HCl - acidic - turns red
• chlorine


  poisonous - wear a mask whilst handling or do it in a fume cupboard
• test for gas - oxygen


  glowing splint

  get a sample of the gas and place the glowing splint into the tube

  oxygen = present = splint relights

  burning required oxygen
• test for gas - hydrogen


  test tube of gas and a burning splint

  move close enough together - hear a squeaky pop
• test for gas - carbon dioxide


  gas sample in one tube and a aqueous solution of Calcium Hydroxide (limewater) - bubble the gas through the solution - should turn cloudy if Carbon dioxide is present

  $CO_2\ (g)+$$Ca\left(OH\right)_2(g)\ \rightarrow\ CaCO_3(s)\ +$$H_2O(l)\$

  $CaCO_3$ = solid = makes it go cloudy
• anion


  negatively charged ion
• Flame test


  identify some metal cations

  different cations produce a different coloured flame when burnt

  1. take a metal loop and sterilise it (dip into dilute hydrochloric acid, rinse in distilled water and then heat over a Bunsen burner)
  2. dip the wire loop into the compound you want to test
  3. hold the wire loop in the clear blue part of the Bunsen burner flame (hottest part)
  4. see what colour the flame turns as the compound burns
• flame test results - Lithium


  crimson
• flame test results - sodium


  yellow
• flame test result - potassium


  lilac
• flame test result - calcium


  orange-red
• flame test result - copper


  green/blue
• flame test - limitations


  have 2 or more different metals in the sample, the colours can mask each other
• flame emission spectroscopy


  flame photometry

  like a flame test - when metal ions are heated they emit light and wavelengths of light

  wavelengths are specific to the particular metal ion being heated

  over comes the flame test problems by using a spectroscope - detects individual wavelengths of emitted light

  intensity of the line on the spectrum indicates the concentration of the ion - use to find concentration of particular ions in a solution
• flame emissions spectroscopy advantages


  sample contains different metals the spectrum will show lines for all
• instrumental methods


  use expensive machinery;

  • very accurate
  • very fast (automated)
  • very sensitive (can detect tiny amounts of substances)
• metal hydroxide test


  react ions with sodium hydroxide solution - see what colour it turns

  result - metal hydroxide is formed - insoluble so appears as a precipitate
• metal hydroxide test - results - aluminium 


  white precipitate that dissolves again

  Al3+(aq) + 3OH-(aq) -> Al(OH)3 (s)
• metal hydroxide test - results - calcium


  white precipitate which doesn't dissolve

  Ca2+(aq) + 2OH-(aq) -> Ca(OH)2(s)
• metal hydroxide test - results - magnesium


  white precipitate which doesn't dissolves

  Mg2+(aq) + 2OH-(aq) -> Mg(OH)2(s)
• metal hydroxide test - results - copper II


  blue precipitate

  Cu2+(aq) +2OH-(aq) -> Cu(OH)2(s)
• metal hydroxide test - results - iron II


  green precipitate

  Fe2+(aq) + 2OH-(aq) -> Fe(OH)2
• metal hydroxide test - results - iron III


  brown precipitate

  Fe2+(aq) +3OH-(aq) -> Fe(OH)3(s)
• cation


  positively charged ion
• carbonate test


  metal carbonates react in hydrochloric acid - they fizz, creating bubbles - bubbles = carbon dioxide - run the gas through limewater - limewater turns cloudy if carbon dioxide is present
• Carbonate + hydrochloric acid -> water + carbon dioxide + salt
• halide tests


  sodium carbonates and potassium carbonates are solutions containing carbonate ions

  1. Put $1cm^3$ of the halide to be tested in a test tube
  2. add 3 drops of nitric acid
  3. Add 1cm of silver nitrate
• results for the halide test - chlorine


  white precipitate
• results for the halide test - bromide


  cream precipitate
• results for the halide test - iodine


  yellow precipitate