A chemistry student prepares a series of simple aqueous dilutions of a monoprotic…
CHEMISTRY · Multi-part · AP · Chemistry · Acids and Bases · Acids and Bases
Problem
A chemistry student prepares a series of simple aqueous dilutions of a monoprotic strong acid and records the pH after each step. 100.0 mL of 0.0100 M HCl is diluted with distilled water to a total volume of 1000.0 mL in a volumetric flask. The resulting solution is then further diluted by transferring exactly 25.0 mL of it into a second 250.0 mL volumetric flask and filling to the mark.
Assume all temperature-dependent quantities remain at 25 °C and that both dilutions are performed quantitatively.
(a) Describe, without performing numerical calculations, how the concentration of H3O+ changes after each of the two dilution steps. Your answer should reference proportional relationships among the relevant volume and concentration variables.
(b) Calculate the numerical value of the final [H3O+] after the two dilutions are completed.
(c) Determine the pH of the final solution, reporting your answer to the correct number of significant figures.
(d) Explain why the pH you obtained is greater than the pH of the original 0.0100 M solution even though the solution is still acidic. In your explanation, connect particle-level concentration changes to the logarithmic nature of the pH scale.