Question

why should AgCl be washed with dilute HNO3 in gravimetric analysis

Answer 1

During gravimetric analysis dilute HNO₃ is used to wash AgCl.There is two reason behind this washing.the first one is the removing excess ions in the precipitate and remove the contaminent from the sample ,via make them free from impuritys.The second thing is the major reason in which it is a chemical approach in which the AgCl precipitate as colloids,when we adding HNO₃ to wash precipitate the solution become slightly acidic and this will eliminate possible interference from weak acids anions,because in HNO₃ the H+ remove HCO₃-,prevent absorption of CO₂ and maintain much higher electrolyte concentration.this higher ionic strength will prevent the pepetization(colloidal dispersion). leads the process of reconversion of colloids and Agcl aggregates.