C2.1.4

• What is the formula of hydrochloric acid and what salt does it form?

  • HCl
  • Chloride
• What is the formula of sulfuric acid and what salt does it form?

  • H2SO4
  • sulfate
• What is the formula of nitric acid and what salt does it form?

  • HNO3
  • Nitrate
• What is the formula of phosphoric acid and what salt does it form?

  • H3PO4
  • Phosphate
• What is the formula of ethanoic acid and what salt does it form?

  • CH3COOH
  • Ethanoate
• An acid is a substance that dissociates in water to release H+ ions
• What is the formula of the alkali sodium hydroxide and what salt does it form?

  • NaOH
  • Sodium
• What is the formula of the alkali Potassium Hydroxide and what salt does it form?

  • KOH
  • potassium
• What is the formula of the alkali ammonia and what salt does it form?

  • NH3
  • Ammonia
• What is the formula of the alkali Ammonium Hydroxide and what salt does it form?

  • NH4OH
  • Ammonium
• What is the formula for the alkali Calcium hydroxide and what salt does it form?

  • Ca(OH)2
  • calcium
• An alkali is a substance that dissociates in water to release OH- ions
• A Strong acid is an acid that completely dissociates in water releasing all of its H+ ions
• A weak acid is an acid that only partially dissociates in water releasing some of its H+ ions
• Neutralisation is a reaction between an acid and an alkali to produce a salt and water
• Ionic equation for neutralisation

  H+ ( aq ) + OH- ( aq ) → H2O ( l )
• Acid + Metal carbonate → salt + carbon dioxide + water
• Metal Oxide + acid → salt + water
• Metal hydroxide + acid → salt + water
• Acid + alkali → salt + water
• Metal + Acid → salt + hydrogen
• Ammonia doesn’t directly produce OH- ions but aqueous ammonia is still an alkali as it reacts with water to produce ammonium and OH- ions :

  NH3 ( aq ) + H2O ( l ) → NH4+ ( aq ) + OH- ( aq )
• The reaction NH3 (aq) + HNO3 (aq) → NH4NO3 (aq) is actually NH4+ (aq) + OH- (aq) + HNO3 (aq) → NH4NO3 (aq) + H20 (l)
• A standard solution is a solution of known concentration
• To prepare a standard solution:

  1. weigh the solid using an accurate balance
  2. Transfer the solid to a beaker washing it from the weighing boat using distilled water
  3. add as much distilled water as is required to dissolve the solid
  4. transfer the solution to a volumetric flask rinsing the beaker and any stirring rod used with distilled water which is also transferred to the volumetric flask
  5. fill the flask up to the graduation line using a dropping pipette when you get close.
  6. put a lid on the flask and slowly invert it several times until thoroughly mixed
• Titration:

  1. add a set volume of a standard solution into a conical flask using a pipette with some indicator
  2. add the unknown solution to the burette and record the initial reading
  3. Take a rough titration adding the unknown to the standard solution swirling the flask as you go. Stop when you get a colour change and record the final burette reading . Calculate the titre by subtracting the initial from the final reading
  4. carry out multiple titrations and calculate an accurate titre
  5. continue carrying out titrations until two accurate titres are concordant
  6. calculate a mean titre
• What accuracy are the burette readings given to?

  to the nearest 0.05 cm3
• How do you add the unknown when carrying out accurate titrations?


  Add the unknown dropwise when you get close to the rough titre
• What is a concordant result?

  Results within 0.1 cm3 of each other
• When calculating a mean titre what do you need to remember?

  to exclude anomalous results
• Name indicators used in titration and describe their changes:

  • Methyl Orange → yellow in alkali , red in acid
  • Phenolphthalein → pink in alkali , colourless in neutral and acid
• A good indicator changes colour very quickly over a very small pH range and has a definite end point
• Pipettes are accurate to plus or minus 0.05 cm3
• Burettes are accurate to plus or minus 0.05 cm3
• in titration results tables all volumes must be to two decimal places ending in a 0 or 5 as burettes are accurate to 0.05 cm3 . The final mean titre is the exception to this rule
• Percentage error equation

  Percentage error = uncertainty of equipment / measurement x 100
• For a titre percentage error the error is timed by two as two readings have been taken
• If when filling the pipette during titration you measure to the top of the meniscus line:

  • the volume of standard solution will be too small
  • the volume of the titre will be too small
  • the concentration will be too high
• If when reading the burette you measure from the top of the meniscus during titration:

  • if you make the same mistake twice it will have no effect as titre volume it is a measure of the difference between the initial and final readings
• If when acid is added to an alkali during titration some solution splashes up the side of the conical flask and a student washes it down with distilled water:

  • the titre volume will remain the same
  • as there is the same amount of moles of alkali in the flask
  • therefore the same amount of acid is required to neutralise it
  • the concentration will be the same