why does the pH of the acid solution initially increase very slowly when metal is first added to the acid solution, but gradually increase at a faster rate as the reaction proceeds to completion?
I thought it may be because the metal is just then being completely dissolved but that didn't make sense because we were instructed to wait until the first little scoop of the metal powder was dissolved before adding the next bit.
1 answer
It would have helped if you had told us about the experiment; I assume you were adding powdered metal to an acid solution. I think the answer is that at first you have MANY H^+ to react with the metal to produce the chloride + H2 gas. As the HCl is used up, the concn of the HCl is decreased, fewer H^+ are available, and the reaction rate is decreased. If I have interpreted the question incorrectly please correct me.