Question
Identification of an unknown powdered metal by reaction with HCl:
Why does the pH of the HCl solution initially increase very slowly when an unknown metal is first added to the acid solution, but gradually increase at a faster rate as the reaction proceeds to completion?
Why does the pH of the HCl solution initially increase very slowly when an unknown metal is first added to the acid solution, but gradually increase at a faster rate as the reaction proceeds to completion?
Answers
DrBob222
If you have a divalent metal the reaction is
M + 2HCl ==> H2 + MCl2
As M reacts H^+ is used which decreases the acidity and make the pH increase. One reason the increase may be slow at first could be due to a coating of the metal oxide on the surface of the metal. It proceeds at a faster rate as the acid eats into the metal and exposes a purer surface.
M + 2HCl ==> H2 + MCl2
As M reacts H^+ is used which decreases the acidity and make the pH increase. One reason the increase may be slow at first could be due to a coating of the metal oxide on the surface of the metal. It proceeds at a faster rate as the acid eats into the metal and exposes a purer surface.
Wallace
pH increases exponentially. Thus, smaller amounts of metal will make greater differences in H3O+ present as metal is added.