Question

In each of the following questions, assume that there is no volume change when HCl is added to water in part (a) or the phosphate buffer in part (c). (a) Calculate the pH when 0.031 moles of HCl are added to 1.000 liter of water. (b) What is the difference between the pH of pure water (pH 7.00) and the pH of the solution after HCl was added? (c) Calculate the pH when 0.031 moles of HCl are added to 1.000 liters of a buffer containing 0.112 M KH2PO4 and 0.383 M K2HPO4 . (d) The pH before the HCl was added is equal to 7.742. What is the difference between the pH before adding the HCl and after adding the HCl?

Answer 1

Part a)

First of all we have to see the reaction occurred or the dissociation of the strong acid HCL in contact with the water:

and the pH to this solution it would be:

Part b)

And the decrease in the ph is due to the strong acid HCL, this acid has a dissociation complete , is the entire H + is adding to the solution, decreasing a lot the ph.

Part C)

Part D)
if the pH of the solution before adding the HCl was 7,742, and after adding it it turned out to be 7.23, it means that the buffer solution worked correctly and its pH was not greatly affected, instead when seeing part a and b of the exercise as the pH of the solution drops considerably due to lack of the buffer, so in this second part the solution is not drastically affected in its acidity