HW 6D.11.

[Yazmin Bocanegra 3L]

6D.11. Decide whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. If pH > 7 or pH < 7, write a chemical equation to justify your answer.

a) NH4Br
b) Na2CO3
c) KF
d) KBr
e) AlCl3
f) Cu(NO3)2

I need help understanding how to determine if the pH is greater or less than 7, and how to come up with a chemical equation to justify the answer.

[SGonzales_3L]

First of all, look at the ions that form each of the compounds. For example, NH₄Br is formed by NH₄⁺ and Br^-. We know that the conjugate bases and acids of strong acids and bases do not affect the pH. HBr is a strong acid due to how easily it loses its H, so Br^- does not affect the pH. NH₄⁺ is the conjugate acid of a weak base, so it will affect the pH. To some extent, it will lose H atoms to form H₃O⁺ ions, making the solution more acidic (pH <7).

To write the equation for this, you can write:
NH_{4 (aq)}⁺ + Br_(aq)^- NH_(aq)3 + Br_(aq)^- + H_(aq)⁺

This equation shows that H⁺ ions are formed in an aqueous solution of NH₄Br. You can replicate this process/analysis for the rest of the compounds.