Chemistry Unit 3

• • Na and Ba flame colour


  yellow and pale green
• chemical anion tests

  add conc. H2SO4

  AgCl2 - ppt gives white fumes

  AgBr2 - ppt gives brown fumes

  AgI2 - ppt gives purple vapour fumes /gas
• apparatus to collect CO2


  diagram

  
• why is ethanoic acid used and not HCl


  ethanoic acid is a weak acid.

  with HCl gas would escape before boiling tube sealed
• why is molar volume value obtained lower than data book

  some co2 escapes before boiling tube sealed

  some co2 dissolves in water
• reduce risk of flammable and harmful to the environment


  use electric heater

  use organic waste bottle
• how do anti-bumping granules make liquids boil smoothly


  ensure gas bubbles are small
• why fractional distillation > simple distillation


  more efficient

  gives longer reaction time

  better separation of products (name them in answer)
• separating funnel diagram


  diagram

  
• -OH group test


  add PCl5

  white fumes seen

  for alcohols, diols
• how to carry out titration

  add acid until close to rough titre value

  add acid drop by drop

  with swirling until solution changes colour
• aldehyde test


  tollen's reagent - silver mirror

  fehling's reagent - red/brown ppt
• ammonia test


  react with HCl (g) - white smoke from ammonium chloride
• water test


  add anhydrous CuSO4 - blue to pink
• C=C test


  bromine water - orange to colourless

  KMnO4 and H2SO4 - purple to colourless
• carbonate ion test CO3 2-


  add HCl (aq)

  effervescence or gas which turns limewater cloudy
• sulfate test SO4 2-


  add BaCl2 and HCl (aq) / Ba(NO3)2 and HNO3 (aq) - white ppt forms
• 1 alcohol to aldehyde to carboxylic acid


  K2Cr2O7 ( orange to green )

  KMnO4 ( purple to colourless )/ H* (from H2SO4)

  heat under reflux - carboxylic acid formed ( if not, distill aldehyde as soon as it forms)
• 2 and 3 alcohol oxidation reactions


  2 alcohol - ketone

  3 alcohol - no oxidation reaction
• 1 alcohol to halogenoalkane


  KBr + H2SO4

  red phosphorous and I2

  PCl5 at room temp
• Reflux

  solution goes from cloudy to clear after anhydrous calcium chloride added

  base added later to neutralise acid
• methyl orange and phenolphthalein

  yellow to orange

  colourless to pink
• Mineral wool used because:

  inert

  holds alcohol in place

  alcohol vapour would not pass over the catalyst slowly enough to react
• observation when adding acidified silver nitrate solution to aqueous solution of ammonium chloride

  white precipitate
• test to confirm presence of NH4+ ions in solution of NH4Cl

  add NaOH and warm

  gas evolved turns red litmus paper blue
• how would experiment change if polysterene cup used instead of glass beaker

  temperature change would be greater

  temperature would rise more slowly

  less heat from surroundings would enter solution
• assumptions made in H= (m x c x T)/n

  solution has a density of 1 gcm^-3

  mass of solid is ignored

  c of solution is the same as water
• State measurements that should be made:

  • mass of each U-tube and contents
  • mass before and after combustion

  
• Give 2 reasons why pure O2 and not air should be used:

  • to exclude water and CO2 from air
  • for complete combustion

  
• Reflux diagram for X and Y when Y is a liquid that is soluble in reaction mixture

  marking points:

  round-bottom flask, still head and thermometer (1)

  condenser with inner tube and labelled water flow (1)

  heat, unsealed collection vessel and left side of apparatus sealed (1)

  
• why are granules of anhydrous calcium chloride used rather than powder


  to allow gases to pass through

  to prevent build-up of pressure
• purpose of anhydrous calcium choride

  to remove water

  as water would otherwise react with product
• suggest why HCl is added drop-by-drop to flask

  to prevent chlorine gas being produced too quickly
• Barium

  it forms a precipitate with chromate ions so it should be removed in titration experiments to prevent this reaction if needed

  reacts with SO4 2- to from solid BaSO4
• why is the first titre not used

  it is not concordant
• how should vigorous effervescence be dealt with

  build up of pressure (in the separating funnel)

  remove the stopper (with the funnel upright)
• why is sodium hydrogencarbonate used

  to remove excess sulfuric acid
• why is cold water bath used in experiment

  reaction is exothermic/vigorous

  mixture may boil causing reactant to escape
• Methyl orange indicator

  yellow in basic solutions

  red in acidic solutions

  at end point it is orange
• Phenolphtalein

  colourless in acidic solution

  pink in a basic solution

  pink at end-point