So as to ensure complete precipitation in gravimetric analysis, an excess of precipitating agent is always used. In gravimetric analysis, barium is precipitated as barium sulphate. No doubt, BaSO4 is a sparingly soluble substance but it possesses a measurable solubility. To decrease its solubility, the concentration of SO42- ions is increased by use of little excess of H2SO4 . The ionic product [Ba2+] [SO42-] exceeds the solubility product of BaSO4 and it is precipitated more completely.
