Performing the Titration

• The key piece of equipment used in the titration is the burette
• Burettes?are usually marked to a precision of 0.10 cm3
  • Since they are analogue instruments, the uncertainty is recorded to?half?the smallest marking, in other words to ±0.05 cm3

   

• The?end point?or?equivalence point?occurs when the two solutions have reacted completely and is shown with the use of an?indicator

The steps in a titration

• A white tile is placed under the conical flask while the titration is performed, to make it easier to see the colour change

Titrating

• The steps in a titration are:
  • Measuring a known volume (usually 20 or 25 cm3) of one of the solutions with a?volumetric?pipette?and placing it into a?conical flask
  • The other solution is placed in the?burette
    • To start with, the burette will usually be filled to 0.00 cm3

     

  • A few drops of the?indicator?are added to the solution in the conical flask
  • The tap on the?burette?is carefully opened and the solution added, portion by portion, to the?conical flask?until the?indicator?starts to change colour
  • As you start getting near to the end point, the flow of the burette should be slowed right down so that the solution is added dropwise
    • You should be able to close the tap on the burette after one drop has caused the colour change

     

  • Multiple runs are carried out until?concordant?results are obtained
    • Concordant results are within 0.1?cm3?of each other

     

   

Recording and processing titration results

• Both the initial and final?burette?readings should be recorded and shown to a?precision?of ?±0.05 cm3, the same as the?uncertainty

A typical layout and set of titration results

• The volume delivered (titre) is calculated and recorded to an?uncertainty?of ±0.10 cm3
  • The?uncertainty?is doubled, because two?burette?readings are made to obtain the?titre?(V final – V initial), following the rules for?propagation of uncertainties

   

• Concordant?results are then averaged, and non-concordant results are discarded
• The appropriate calculations are then done

Answer

Step 1:?Calculate the average titre

• • Average titre 22.80 cm3

Step 2:?Calculate the number of moles of sodium hydrogencarbonate

• • Moles ?moles

Step 3:?Calculate (or deduce) the number of moles of hydrochloric acid

• • The stoichiometry of NaHCO3?: HCl is 1 : 1
  • Therefore, the number of moles of sodium hydrogencarbonate is also 4.56 x 10-3?moles

Step 4:?Calculate the concentration of hydrochloric acid

• • Concentration?