Activity 1: Conductometric titration of aspirin

Activity summary

What you must remember :
  • Conductivité
  • Conductivité ionique molaire

  Skills linked to the curriculum:

Compétences Capacités à maîtriser
 ANA Interpréter qualitativement l'allure de la courbe de titrage par suivi conductimétrique en utilisant des tables de conductivités ioniques molaires et en déduire le volume à l'équivalence du titrage.
 RÉA Réaliser un protocole de titrage mettant en jeu une réaction suivie par conductimétrie.


Formuler et argumenter des réponses structurées.
Formuler et présenter une conclusion.

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Conductivity method can be used as a simple and convenient technique for determining the concentration of weak acids such as acetylsalicylic acid. During the titration of the following reaction occurs:


Fig. 1. Reaction of Acidum Acetylsalicylicum with sodium hydroxide


Document 1: Conductometric measurements

Initially the conductance is low due to the feeble ionization of acetylsalicylic acid. The conductance increases on adding NaOH as it neutralizes the undissociated acetylsalicylic acid to its sodium salt which is the strong electrolyte. This increase in conductance continues to rise up to the equivalence point. The graph near the equivalence point is curved due the hydrolysis of salt. Beyond the equivalence point, conductance increases more rapidly with the addition of NaOH due to the highly conducting OH^- ions resulting in the disappearance of slightly dissociated acid, in place of which occurs a completely dissociated sodium salt, which has a higher conductivity than the undissociated acid form. The equivalence point of titration is determined by drawing a tangent to the titration curve (before and after equivalence point, Fig.4).

Document 1
Fig. 4. Determination of equivalence point


Document 2: Materials and methods

  • Conductometer
  • Magnetic stirrerSingle-Channel Pipette 1mL
  • Volumetric pipettes 100mL
  • Measuring cylinder 50mL
  • Volumetric flask 250mL
  • Beaker 150mL
  • 0,1M NaOH solution
  • C2H5OH


Document 3: Procedure

Sample preparation
Check the weight of the drug tablet on an analytical balance, place the tablet in a volumetric flask (250mL). Add 15mL of distillated water and 30mL of ethanol to volumetric flask and mix it until tablet is dissolved. Fill volumetric flask to the mark, place a stir bar inside and continue mixing for 5 min.

Pipette into a beaker 100mL of the solution. Place in a beaker and stir bar and conductivity cell. Each time add 0,5mL of NaOH solution to summary volume of 15mL, mix the solution for 1min, stop the stirrer before conductivity measurement. Write down the results.


Acquiring vocabulary

English French
measuring cylinder  

Understanding the process
Carry out the experiment.

Present your results orally and try to answer the problem: what is the initial mass of aspirin in an aspirin tablet?

Last modified: Sunday, 7 January 2018, 9:23 PM