the probability of an analyte precipating goes up drematically as the number of precipating ions surrounding it. The likehood of a precipation greatly increases.
Like one girl at a dance, and 56 boys. You are most likely to find her surrounded by boys, and in fact, dancing (precipating) often.
Why is it important in gravimetric analysis to add an excess amount of precipitating ions to a solution containing an analyte
2 answers
Since we have so many people dancing here let me dance too.
Another reason, and just as important, is to utilize the common ion effect of the excess ion. In doing so you shift the equilibrium, just as Le Chatelier said will happen, and you DECREASE the solubility of the stuff being pptd and that makes recovery that much better. In fact, to emphasize Bob Pursley's point, some quantitative procedures are NOT quantitative UNLESS there is an excess of the ppting agent present.
Another reason, and just as important, is to utilize the common ion effect of the excess ion. In doing so you shift the equilibrium, just as Le Chatelier said will happen, and you DECREASE the solubility of the stuff being pptd and that makes recovery that much better. In fact, to emphasize Bob Pursley's point, some quantitative procedures are NOT quantitative UNLESS there is an excess of the ppting agent present.
2 answers