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Question

Which Titration Is Known As Argentometric Titration?


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Solution

  1. Argentometric titrations are those that use Silver nitrate (AgNO3) as the titrant. Such titrations are used to determine the concentration of Chloride ions (Cl-), Bromide ions (Br-), Cyanide ions (CN-) etc. through the formation of their complexes or salts with Silver nitrate.
  2. For example, in the argentometric titration of Potassium cyanide (KCN), a white precipitate is formed with the addition of Silver nitrate which dissolves on stirring. This is due to the formation of Potassium silver cyanide (K[Ag(CN)2]) which is a stable, soluble salt.

AgNO3(aq)+2KCN(aq)K[Ag(CN)2](aq)+KNO3(aq)

3. At the end point, when all the cyanide ions have been consumed, any further addition of Silver nitrate solution yields the insoluble Silver argentocyanide (Ag[Ag(CN)2]). Thus, the end point is marked by the appearance of turbidity.

AgNO3(aq)+K[Ag(CN)2](aq)Ag[Ag(CN)2](s)+KNO3(aq)

4. For determining the concentrations of Chloride and Bromide ions, a small amount of Potassium chromate (K2CrO4) is added as an indicator.

5. For instance, during the argentometric titration of Sodium chloride (NaCl), Silver nitrate reacts to give Silver chloride before the end point since Silver chloride is less soluble.

6. At the end point, once all the chloride ions are consumed, further addition of Silver nitrate will yield the yellow, insoluble salt of Silver chromate.

AgNO3(aq)+NaCl(aq)AgCl(aq)+NaNO3(aq)(Beforeendpoint)2AgNO3(aq)+K2CrO4(aq)Ag2CrO4(s)+2KNO3(aq)(Atendpoint)


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