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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?

  • Chemistry -

    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.

  • Chemistry -

    pH increases exponentially. Thus, smaller amounts of metal will make greater differences in H3O+ present as metal is added.

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