TITRAGE CONDUCTIMÉTRIQUE / Exercice / Terminale

Main Ideas and Concepts

• Titration Reaction: The reaction involves Ag+ ions reacting with Cl- ions to form AgCl precipitate.
• Conductivity Changes: The Conductivity of the solution changes during the titration process, initially decreasing and then increasing.
• Rocknech Relation: Conductivity is determined by the sum of the products of the ionic molar conductivities and the concentrations of the ions present.
• Ionic Species Involved:
  • Before Equivalence:
    • Magnesium ions (Mg2+) are spectator ions and do not react, so their concentration remains constant.
    • Chloride ions (Cl-) decrease in concentration as they react with Ag+ ions.
    • Silver ions (Ag+) start at zero concentration and increase after the equivalence point since they no longer react.
    • Nitrate ions (NO3-) are also spectator ions and increase in concentration as they are added.
• Conductivity Analysis:
  • Before the equivalence point, the decrease in Chloride ions (which have a higher molar Conductivity) leads to a decrease in overall Conductivity.
  • After the equivalence point, the concentration of ions that contribute to Conductivity increases, resulting in an overall increase in Conductivity.

Methodology/Instructions

• Create a table to track the concentrations of ions before and after the equivalence point.
• Analyze the behavior of each ion:
  • Spectator Ions: Mg2+ and NO3- do not change their role in the reaction.
  • Reactive Ions: Cl- decreases before equivalence, while Ag+ increases after equivalence.
• Compare the molar ionic conductivities of the ions to determine the overall change in Conductivity:
  • Recognize that higher Conductivity of Cl- leads to a decrease in overall Conductivity before equivalence.
  • Acknowledge that after the equivalence, as reactive ions are added, Conductivity increases.

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