Identifying salts as acidic, basic, or neutral

[Nicole Nakama 1A]

This topic came up on Achieve and read other responses on this forum, and I'm still not too sure. I understand deriving the molecule into its cations and anions but how do we know where each came from? What's the thought process?

[Chem_Mod]

I am not entirely sure what you mean, since I am slightly confused by the question.... but if a strong acid reacts with a weak base, the salt will be acidic. If a strong base reacts with a weak acid, the salt will be basic.

Hope this helps.

[Caitlin Pan 1J]

I’m not too sure if this method is correct but the way I approach these questions is assume that the salts are separated into their cations and anions. Then if they’re the cations, they are essentially the conjugate acids of a base. For example if the cation is Na+, then I assume Na+ is the conjugate acid of the base NaOH. The stronger the base is, the weaker the conjugate acid will be. Since NaOH is a strong base, then Na+ will be a very weak base. This is the same case for anions. Anions are the conjugate base of an acid and if the corresponding acid (HCl for Cl-) is a strong acid, this implies that the anion is a very weak base and therefore negligible (basically neutral). Essentially, if the corresponding acids/bases of the ions from the salt are strong, this means that the ions themselves are very weak. if the corresponding ions from the salt are weak, then the ions themselves are significant enough to affect the pH.
For example, if given a salt like NH4Cl, Cl- would be a very very weak conjugate base (since the corresponding acid is HCl, which is an extremely strong acid) and would therefore not affect the pH in any significant way. NH4+ would be a conjugate acid to a relatively weak base (NH3), which means that it would actually affect the pH of the solution. Therefore, the salt NH4Cl would be acidic in nature. Hopefully this makes sense in some way!

[Nikki Ma 3B]

this is how I did the identifying back in chem 14a
first part: anion
1. neutral: if in group 1 or group 2 ; a charge of +1
2. everything else --> acidic (conj acid of weak base)

second part: cation
1. basic: base of weak acid
2. neutral: base of strong acid
3. acidic: HSO4- , H2PO4. (there is more but those are a few)

hope that helps !!

[John_Sunthorn_3B]

How I identify salts as acidic, basic, or neutral is based on the chemical reaction that leads to the creation of that salt. Like the posts prior to mine, an strong acid + weak base = acidic salt; a weak acid + a strong base = basic salt; a strong base + acid = neutral salt; and a weak acid + weak base = neutral salt. I'm not sure as to the line of reasoning behind why salts are acidic or basic, but the way I justify calling a particular salt acidic or basic is by the acid + base combination that made them. Remember that a cation is from the acid (as the acid donates the hydrogen), and the anion is from the base (as the base contains hydroxide, which combined with the hydrogen donated from the acid to form H2O), so I recommend remembering the cations that form strong acids and anions that are a part of strong bases, as you would need to use that on top of the reasoning above to know how to identify a salt's acidity.

[jessicahedayi1H]

Hi,

Here's how I approached this type of question. We know
strong acid + weak base = acidic
weak acid + strong base = basic
weak + weak = neutral
strong + strong = neutral

I would write the salt and dissociate it into cation and anion. If it was a cation, I would put OH- with it. If it was an anion, I would put H+ with it. As mentioned above, the cations can be viewed as the conjugate acids of a base, while the anions can be viewed as the conjugate base of an acid. I would then check to see if either was considered a strong or weak acid/base. Based upon this, I would classify the salt as the combination of acid and base.

For ex, say you're given LiNO3 as a salt and asked to classify it. I would check the charges on Li (+) and NO3 (-). Now you have the cation and anion. Since Li has a positive charge, I put it with OH- to create LiOH (strong base). For NO3, it becomes HNO3 (strong acid). Strong acid + base = neutral salt.