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# Acid–base properties of salts

We can determine whether a salt solution will be acidic, basic, or neutral by considering the reactivity of both the cation and the anion with water. If neither species reacts with water, the solution will be neutral. If only the cation reacts with water, the solution will be acidic. If only the anion reacts with water, the solution will be basic. If both species react with water, the pH of the solution will depend on the relative strengths of the cation and the anion.

## Want to join the conversation?

• why Na+ cant react with water ?
• Na+ is a cation, having a positive charge. Needing a negative charge from water, it could potentially react with either H+ or OH-. H+ doesn't work since it has a positive charge. OH- does not work because the supposedly formed substance would be NaOH, a strong base. Strong bases are not formed since they dissociate to near completion.
• What about a weak acid interacting with a weak base - would the solution be neutral? Or would the pH of solution be slightly greater or slightly less than 7 depending on the relative Kb and Ka of each? Would a salt still form in any case?
• I am assuming that you are adding equimolar amounts of the weak acid and weak base. Yes, the salts A⁻ and BH⁺ would still be formed.
HA + B --> BH⁺ + A⁻
After being formed, the salts will undergo salt hydrolysis.
A⁻ + H2O <--> HA + OH⁻
BH⁺ + H2O <--> B + H3O⁺
The extend of salt hydrolysis depends on the strength of the conjugate base(A-) and conjugate acid (BH⁺) respectively. Kb (conj base) = Kw / Ka (acid) and Ka (conj acid) = Kw / Kb (base)
If Kb (conj base) > Ka (conj acid), then the solution would be basic.
One line answer, if Ka of the weak acid is more than the Kb of the weak base, the resulting solution would be acidic.
• Why does cl- not react with water?
• I am uncertain how it can react... Water consists of H2O, which may turn into H+ OH-. but the Cl- will not react with H+ to reform HCl because that dissolves in water. Also, things tend to arrange themselves to increase entropy, and free floating ions have higher entropy
(NH4)2(SO4) + Ca(OH)2 and it said the products would be ---> CaSO4 + 2NH3 + 2H2O

Could someone please tell me why this is the answer? Any help would be appreciated :)
• It's a two-part reaction. The first part is a double displacement reaction.
(NH₄)₂SO₄(aq) + Ca(OH)₂(aq) → 2CaSO₄(s) + 2NH₄⁺(aq) + 2OH⁻(aq)
The second part is an acid-base neutralization.
2×[NH₄⁺(aq) +OH⁻(aq) → NH₃(aq) + H₂O(l)]
• Why is the stronger the acid the weaker its conjugate base?
(1 vote)
• Think about the strength of an acid as its tendency to release a proton. So, the stronger the acid the more it wants to get rid of the acidic proton. In that sense, the formed conjugate base will be strong or weak? will it want to pull the proton strongly or weakly?

Because the strong acid really wants to get rid of the proton, the formed conjugate base will be weak in garbing a proton, because as soon as it's protonated the acid will release the proton.
• At about , after the acetate anion reacts with water and "produces" OH- why won't the OH- react back with the free Na+ ion and go back to the beginning of having an acid and base, then split again and so forth?
• NaOH is a strong base, so it is unlikely to re-associate in solution. It tends to dissociate in any aqueous solution.
• What if you were dissolving a salt like NaHCO3 and it had multiple steps? How do you find the pH? How would you know the relative concentration of different species?
• towards the end, why does the NH4+ go into a separate equation and react with H2O?
• Because if you have NH4+ In solution it will react with H2O...
Whereas Cl- won’t
• If 90g of sodium hydroxide (aq) is added to hydrochloric acid,which salt will be formed?
• NaCl in my idea
according to the reaction: NaOH + HCl = NaCl + H2O