1)Ppt should be easy to wash free of contaminants without loss of the ppt either in solution or through the filter. The particle size should be large enough not to escape through the pores of the filter.
2) The desired substance must be completely precipitated. In most determinations the ppt is of such a low solubility that losses from dissolution are negligible. The common ion effect further reduces the solubility of the ppt. This pushes equilibrium to the right .We can further decrease the solubility of the ppt by using a nice bath
3) The ppt must be of a known composition
4) The ppt should be pure or free from any impurities. Careful pption and sufficient washing helps to reduce levels of impurities
5) The ppt should not react with the atmosphere and it must have a known composition which remains stable after drying

Criteria for a successful determination