A research chemist begins with 5.00 mL of 12.0 M HCl (concentrated hydrochloric acid)…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
A research chemist begins with 5.00 mL of 12.0 M HCl (concentrated hydrochloric acid) at 25 °C. The chemist performs the following serial dilutions, using volumetric flasks and quantitative transfers:
• Step 1: Transfer the 5.00 mL aliquot into a 250.0 mL volumetric flask and dilute to the mark.
• Step 2: Withdraw 10.00 mL of the Step 1 solution, place it into a 100.0 mL volumetric flask, and dilute to the mark.
• Step 3: Withdraw 20.00 mL of the Step 2 solution, place it into a 1.000 L volumetric flask, and dilute to the mark.
(a) For each of the three steps, calculate the molarity of HCl in the flask after dilution.
(b) Using your results from part (a), compute the final [H3O+] present after Step 3.
(c) Determine the pH after Step 3. Show that the value is greater than 0 but less than 7, and explain the chemical significance of such a pH relative to more concentrated acidic solutions.
(d) Suppose an error led to withdrawing only 9.80 mL, rather than 10.00 mL, in Step 2. Calculate the resulting percent error in the final pH and discuss whether this deviation would be experimentally significant.