Required practical : Neutralisation

• How do you find the determination of the reacting volumes of solutions of strong acid and strong alkali by titration? ( part 1 )

  • Use a graduated pipette and filler to put exactly 25cm3 of the sodium hydroxide into the conical flask, place on white tile
  • Clamp the burette vertically + fill with hydrochloric acid
  • Put 5 drops of methyl orange into conical flask
  • Open the tap of the burette so that acid flows into the conical flask at a drop by drop rate .
• How do you find the determination of the reacting volumes of solutions of strong acid and strong alkali by titration? ( part 2 )

  • swirl to make sure it is mixed thoroughly
  • Close the tap when the colour of the indicator just changes from yellow to red
  • Read the burette to the nearest 0.05cm3
  • Repeat experiment until you get concordant results
  • Calculate a mean, discarding any non-concordant results.
• Calculation - Imagine the mean volume of sulphuric acid was 16.07cm3 and the concentration of NaOH used was 0.1mol/dm3.

  Step 1 = 2NaOH + H2SO4 -> Na2SO4 + H2O

  Step 2 = Moles NaOH = C x V = 0.1mol/dm3 x 0.025dm3 = 2.5 x 10^-3mol
• Calculation - Imagine the mean volume of sulphuric acid was 16.07cm3 and the concentration of NaOH used was 0.1mol/dm3.

  Step 3 = Moles H2SO/Moles NaOH = 1/2

  So moles H2SO4 = 1/2 x moles NaOH

  So moles H2SO4 = 0.5 x ( 2.5 x 10^-3 ) = 1.25 x 10^-3mol

  Step 4 = Concentration = moles/volumes = ( 1.25 x 10^-3 ) x 0.01607 = 0.078mol/dm3
• Phelnolphthalein pink in alkali
• Methyl orange red in acid and yellow in alkali