Being amphoteric SnO2 reacts both with HCl and NaOH. SnO2 reacts with HCl to form SnCl4 . Adsorption of Sn4+ results formation of a positively charged colloidal sol SnO2 reacts with NaOH to form Na2SnO3 . Adsorption of SnO32− results formation of a negatively charged colloidal sol.