Salt Cation & Anion

[006058674]

Hi,
I was wondering how to tell if a salt has a basic/acidic anion or cation, and how/if we can use that to identify whether a salt is acidic or basic (and strong or weak).
Some examples that Dr. Lavelle gave in class were HF, CH3COOH, HCOOH, NaF, NaCH3COO, and NaHCOO.
Thank you :)

[Julia Chow]

Hello -
In order to determine whether a salt is acidic or basic, you must first dissociate the salt into its cation and anion. Then, react each ion with H2O and write out the products (cations will create H+ and anions will create OH-). If the the conjugate base of the cation is a strong base, while the conjugate acid of the anion is a weak acid, then the salt will be basic. If the conjugate base of the cation is a weak base, while the conjugate acid of the anion is a strong acid, then the salt will be acidic. If the conjugate base is a strong base AND the conjugate acid is a strong acid, then the solution will be neutral.

I recommend practicing with the salts on week 3 achieve #6.

[Bridgette Ryning 1D]

Exactly. The salt will dissociate in an aqueous environment and the cation (positive) will connect with the negative OH molecules and the anions (negative) will connect with the positive hydronium ions. If the conjugate base (it wants to add to the OH, take that H) of the cation creates a strong base this means it will dissociate so there will be a lot of -OH in the solution making it basic (especially when the conjugate acid of the anion is weak, so it will stay together and keep that H+ from floating around and make the solution more acidic). The reverse is true for having a strong conjugate acid and a weak conjugate base. If they are both strong then the ratio of -OH and H3O+ is even and the solution will be neutral.