`SnO_2` forms a positively charged colloidal sol in the acidic medium and negatively charged sol in the basic medium. Explain.

Explanation

`SnO_2` is of amphoteric in nature which means that it can react with both acids and bases. With an acid such as HCl, if forms `SnCl_4`. The` Sn^(4+)` ions are adsorbed on the surface of `SnO_2` to give a positively charged colloidal sol.
`SnO_2+4HCl to SnCl_4+2H_2O and SnO_2+Sn^(4+) to [SnO_2]Sn^(4+)`
Similarly with base like NaOH, if forms sodium stannate `(Na_2SnO_3)`. The stannate ions get adsorbed on the surface of SnO2 to give negatively charged colloidal sol.
`SnO_2+2NaOH to Na_2SnO_3 and SnO_2+SnO_3^(2-) to [SnO_2] SnO_3^(2-)`