Question

why is it less effective to wash an insoluble precipitate with 15 ml of water once than it is to wash the precipitate with 3 ml of water 5 times ?

Answer 1

It is less effective to wash an insoluble precipitate with 15 ml of water once than it is to wash the precipitate with 3 ml of water 5 times because commonly, when you clean an indissoluble precipitate with water, the water will not be completely saturated with contaminates. Therefore, the absorption of the contaminates would lower with each wash, since if you only washed it once with a bigger amount or volume of water, it’d become less contaminated with the wash water but it wouldn’t get rinsed numerous times.