2010 Final Question 4B

[Kira Conde 2O]

Hello,

I am attempting 2010 final question 4B and it honestly just seems so hard to me. There are buffers and PH involved, and though we learned those in 14A, they are really confusing me. The question reads:

When a pH meter was standardized with boric acid-borate buffer with a pH of 9.40, the cell emf was .060 V. When the buffer was replaced with a solution of unknown hydronium ion concentration, the cell emf was .22 V. What is the pH of the solution. Please help! The pH questions in electrochem are really giving me a hard time!

[Chem_Mod]

Q = H⁺ A^-/HA

In a buffer system (A) ≈ (HA), we can write Q = H⁺

Then use the Nernst equation where Q = H⁺ and since you have the pH and E = +0.060 V you can calculate E^o.

Then in the 2nd part you can calculate Q using the same E^o and E = +0.22 V.