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I believe if the salt has an anion and cation from both a strong acid and strong base, it will not affect the pH. One of the Sapling questions for this week explained this in depth in the solution, so I would recommend looking for that!!
Dr. Lavelle said that Group 1 and 2 metal cations do not affect pH because they are not strong enough to affect the water molecule's bonds. Also, the conjugate base (anion) of a weak acid will raise the pH. You can use these two concepts to help determine if a salt will affect pH.
Salts do not have to be either a weak acid or a weak base, some salts can be neutral. For example, Dr. Lavelle said that Na+ and Cl- both do not affect the pH. Therefore, NaCl is a neutral salt. Salts that act as weak acids include ones where nitrogen has 4 bonds and one of them is a hydrogen, ones containing small highly charged metal cations, and ones that contain the anion HSO4- or H2PO4-. Salts that act as weak bases are ones that contain the anion/conjugate base of a weak acid. I hope this helps!
Some salts are neutral salts, and they generally come from the reaction between a strong acid and a strong base. In addition, the ions of a neutral salt in water aren't effective in changing the pH of a solution.
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