Question

What is a completeness of preciptation and why is it important?

Answer 1

Completeness of Precipitation.

Precipitating an ion in solution as an insoluble compound by addig an EXCESS of the precipitating reagent is known as completeness of precipitation

In qualitative analysis of metal ions, whenever an ion is to be removed from a solution by precipitation, one must check to be sure that the ion has been COMPLETELY removed from the solution. Otherwise the metal ion which is not completely removed may interfere in the analysis of other metal ions

The ensure completeness of precipitation, remove the filtrate from the precipitate, place it in a clean test tube and add to it one to two drops of the reagent being used as the precipitating agent. If no new precipitate forms the precipitation is complete. If more precipitate forms, add 2-3 more drops of the precipitating reagent to the filtrate, recentrifuge and combine the precipitates with a small amount of distilled water. Repeat this procedure till no precipitate is formed on adding the precipitating reagent