`SnO_(2)` forms positively charged colloidal sol in acidic medium and negatively charged colloidal sol in basic medium. Explain ?

Explanation

`SnO_2` is amphoteric in nature and reacts with acids as well as bases. It reacts with acids, e.g., HCl to form `SnCl_4` in solution. The common `Sn^(4+)` ions are adsorbed on the surface of `SnO_2` forming positively charged sol :
`SnO_2 + 4HCl to SnCl_4 + 2H_2O`
`SnO_2 + Sn^(4+) to underset("Positive sol")(SnO_2 : Sn^(4+)`
`SnO_2` reacts with a base e.g., NaOH to form sodium stannate `(Na_2SnO_3)` in the solution. The stannate ions are adsorbed on the surface of `SnO_2` to from negatively charged sol.
`SnO_2 + 2NaOH tounderset("Sodium stannate")(Na_2SnO_3 + H_2O)`
`SnO_2 + SnO_3^(2-) to underset("Negative sol")(SnO_2 : SnO_3^(2-))`