Question

QUESTION 44 5 points Save Answer A 0.5-L unbuffered solution needs the pH adjusted from 6.8 to 2.5. How many microliters of a 6 molar HCl solution need to be added to adjust the pH? Report your answer to four decimal places. For this question: • Assume the volume of HCl being added is negligible and the total volume of the solution does not change. • The volume of the solution is *not* 1 L like it was in the practice pools. • The question requests your answer be reported in PL (microliters)!! Name: Duration: Added: Calculating ChangelnpH (04:33) 04:33 15 Jan 2018 04:04 PM Watch Media

Answer 1

let the volume required is x L

moles of acid = molarity * volume = 6 * x = 6x moles

desired change in pH = 6.8 - 2.5 = 4.3

so [H+] = 10^-pH = 10^-4.3 = 0.00005

since volume of soln is constant

hence moles of [H+] = change in conc * volume = 0.00005 * 0.5 = 0.000025

hence

0.000025 = 6x

x = 0.000004 L or 4uL

since 1L = 10^6 uL