Required activity 1. Titrations

• Titrations


  1. Done often to find out the concentration of one substance by reacting it with another substance of known concentration

  2. Often done with neutralisation reactions, but can be done with redox reactions
• Detailed Method for Titration

  1. Rinse pipette with substance to go in it (often alkali)

  2. Pipette 25 cm3 of solution A into conical flask, ensuring the bottom of the meniscus sits on the marked line

  3. Touch surface of solution with pipette to ensure correct amount is added

  4. Use a conical flask for easier swirling of the mixture without spilling the contents
• General Method for Titration

  1. Rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water)

  2. Pipette 25 cm3 of alkali into conical flask

  3. Touch surface of alkali with pipette to ensure correct amount is added

  4. Add acid solution from burette

  5. Ensure the jet space in the burette is filled with acid

  6. Add a few drops of indicator and refer to colour change at end point

  7. Use a white tile underneath the flask to help observe the colour change

  8. Add acid to alkali whilst swirling the mixture and add acid drop wise at end point

  9. Note burette reading before and after addition of acid

  10. Repeat titration until at least 2 concordant results are obtained- two readings within 0.1 of each other
• The burette should be rinsed out with the substance that will be put in it to avoid dilution or reaction with residual water or substances from previous titrations
• Do not leave the funnel in the burette to prevent small drops of liquid falling and giving a false burette reading
• Make sure the jet space in the burette is filled with the solution and air bubbles are removed
• Titration


  1. Don’t leave the funnel in the burette because small drops of liquid may fall from the funnel during the titration leading to a false burette reading

  2. Make sure the jet space in the burette is filled with the solution and air bubbles are removed

  3. If the jet space in the burette is not filled properly prior to commencing the titration it will lead to errors if it then fills during the titration, leading to a larger than expected titre reading

  4. Read the bottom of the meniscus on the burette

  5. Add a few drops of indicator and refer to colour change at end point

  6. Add solution from burette whilst swirling the mixture and add drop-wise at end point

  7. Note burette reading before and after addition of solution

  8. Repeats titration until at least 2 concordant results are obtained- two readings within 0.1 of each other

  9. Distilled water can be added to the conical flask during a titration to wash the sides of the flask so that all the acid on the side is washed into the reaction mixture to react with the alkali

  10. Recording results should be clearly recorded in a table

  11. Record titre volumes to 2dp (0.05 cm3)

  12. Working out average titre results only make an average of the concordant titre results
• Indicators are generally weak acids so only add a few drops of them. If too much is added they will affect the titration result
• Distilled water should be used to wash out conical flasks between titrations because it does not add any extra moles of reagents
• Only distilled water should be used to wash out conical flasks between titrations because it does not add any extra moles of reagents
• If acid is added from the burette the colour change would be pink (alkali) to colourless (acid): end point pink colour just disappears [use with titrations using strong alkalis e.g. NaOH]
• Methyl orange is a suitable indicator for neutralisation reactions where strong acids are used. It is red in acid and yellow in alkali. It is orange at the end point
• Results should be recorded in full (i.e. both initial and final readings)
• lf 2 or 3 values are within 0.10cm3 and therefore concordant or close then we can say results are a
• Recorded in a table

  • Titration number
  • Initial burette reading (cm3)
  • Final burette reading (cm3)
  • Titre (cm3)
• Working out average titre results

  1. Only make an average of the concordant titre results

  2. If 2 or 3 values are within 0.10cm3 and therefore concordant or close then we can say results are accurate and repeatable and the titration technique is good and consistent
• Safety precautions: Acids and alkalis are corrosive (at low concentrations acids are irritants)
• Safety precautions: Wear eye protection and gloves
• Safety precautions: If spilled immediately wash affected parts after spillage
• Safety precautions: If substance is unknown treat it as potentially toxic and wear gloves
• Repeating a single titration allows for anomalous titres to be spotted and discounted
• In quality control, it will be necessary to do titrations/testing on several samples as the amount/concentration of the chemical being tested may vary between samples
• If titrating a mixture to work out the concentration of an active ingredient, it is necessary to consider if the mixture contains other substances that have acid base properties
• If substances in a mixture don't have acid base properties, we can titrate with confidence
• Common Titration Equations


  • CH3CO2H + NaOH → CH3CO2-Na+ + H2O
  • H2SO4 + 2NaOH → Na2SO4 + 2H2O
  • HCl + NaOH → NaCl + H2O
  • NaHCO3 + HCl → NaCl + CO2 + H2O
  • Na2CO3 + 2HCl → 2NaCl + CO2 + H2O
• Detailed Procedure: how much iron is in iron tablets

  1. Weigh accurately two 'ferrous sulphate' tablets

  2. Grind up the tablets with a little 1 mol dm-3 sulphuric acid, using a pestle and mortar

  3. Transfer the resulting paste into a 100cm3 volumetric flask

  4. Add sufficient 1 mol dm-3 sulphuric acid to make up the solution to exactly 100cm3

  5. Titrate 10.0 cm3 portions of the solution with 0.0050 M potassium manganate(VII). The end-point is marked by the first permanent purple colour
• The redox titration between Fe2+ with MnO4– (purple) is a very common exercise
• The purple colour of manganate can make it difficult to see the bottom of the meniscus in the burette
• If the manganate is in the burette, then the end point of the titration will be the first permanent pink colour
• The presence of manganate can make it difficult to see the bottom of the meniscus in the burette
• If the manganate is in the burette

  The end point of the titration will be the first permanent pink colour
• Choosing correct acid for manganate titrations

  • Only use dilute sulfuric acid
  • Avoid acids that set up alternative redox reactions
  • Avoid using weak acids like ethanoic acid
  • Avoid using conc HCl
  • Avoid using nitric acid
• Insufficient volumes of sulfuric acid will mean the solution is not acidic enough and MnO2 will be produced instead of Mn2+
• The brown MnO2 will mask the colour change and lead to a greater (inaccurate) volume of manganate being used in the titration
• Using a weak acid like ethanoic acid would have the same effect as it cannot supply the large amount of hydrogen ions needed (8H+)
• Conc HCl should not be used as the Cl- ions would be oxidised to Cl2 by MnO4- as the Eo MnO4-/Mn2+ > Eo Cl2/Cl-
• Using conc HCl would lead to a greater volume of manganate being used and poisonous Cl2 being produced
• Nitric acid should not be used as it is an oxidising agent. It oxidises Fe2+ to Fe3+ as Eo NO3-/HNO2 > EoFe3+/Fe2+
• Using nitric acid would lead to a smaller volume of manganate being used
• A 2.41g nail made from an alloy containing iron is dissolved in 100cm3 acid. The solution formed contains Fe(II) ions. 10cm3 portions of this solution are titrated with potassium manganate (VII) solution of 0.02M. 9.80cm3 of KMnO4 were needed to react with the solution containing the iron. Calculate the percentage of iron by mass in the nail