Analysis of a spring water

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Determination of Cl- ions with a selective electrode (potentiometry)

Electrode constitution

The selective electrode for chloride ions Cl– consists of:

  • A pellet-shaped silver sulphide (Ag2S) and silver chloride (AgCl) poly-crystalline membrane situated at the end of a plastic cylinder.
  • An internal reference electrode made of a silver wire which is inserted into the pellet.

Ag+ ions are able to migrate in the pellet (particularly in the external part). The potential of the electrode depends on the concentration of the Ag+ ions (and Cl- via the Ks of AgCl). This type of electrode is said to be “all solid”. Some selective electrodes for chloride ions containing a silver chloride solution are also available on the market.

Illustration of two selective electrodes in profile view. One "all solid", with the silver wire inside, and at the base a thick membrane in contact with the silver wire. The other one: the silver wire is immersed in a solution of remplissafe (AgCl), the membrane at the base is thinner and is not in direct contact with the silver wire.
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