Addition of excess `AgNO_(3)` to NaCl solution gives positively charged AgCl sol, while `AgNO_(3)` solution on treating with excess of NaCl solution yields negatively charged AgCl sol. Explain with reason.

Explanation

Sol particles acquire electrical charge by adsorbing positive or negative ions from the solution in which they are prepared. If the solution contains more than one ion of a particular type (positively or negatively charged), then the ion common to the sol particle is adsorbed. When an excess of `AgNO_(3)` solution is added to NaCl solution, a positively charged AgCl sol is obtained. This is because the sol particles of AgCl adsorb `Ag^(+)` ions, which being present in excess, and convert to positively charged particles `AgCl: Ag^(+)`. On the other hand, if an excess of NaCl solution is added to `AgNO_(3)` solution, a negatively charged AgCl is obtained. `Cl^(-)` ions being present in excess are adsorbed by the sol particles of AgCl, leading to the formation of negatively charged particles `AgCl:Cl^(-)` .