Basic and Acidic Salts

Practice Question Solving
1

Can basic or acidic salts be classified into strong or weak bases/acids? Or are they always weak?
For example,
HF + H2O <=> H3O+ + F-
F- is a strong conjugate base. But if it reacted with a Na+ ion to form NaF, what would NaF be? How does the formation of a salt affect any given conjugate acid or base that was ionized from actual strong/weak acids/bases?

Edit:
Bonus question: How come strong acids like HCl have rate constants, in this case Ka, when -in theory- they shouldn’t have equilibrium because the reaction favours the products and HCl will fully ionize? Is it because in practice strong acids/bases don’t completely dissociate?

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2

Hi
Isn’t HF a weak acid?

3

yes HF is a weak acid

4

  1. Can basic or acidic salts be classified into strong or weak bases/acids?

    • Salts derived from strong acids and strong bases typically do not affect the pH of the solution (i.e., they’re neutral salts), such as NaCl.
    • Salts derived from weak acids and strong bases (like CH3COONa) will produce a basic solution upon dissolution because the conjugate base of the weak acid will be a stronger base than water.
    • Salts derived from strong acids and weak bases (like NH4Cl) will produce an acidic solution upon dissolution because the conjugate acid of the weak base will be a stronger acid than water.
    • Salts derived from weak acids and weak bases can be either acidic or basic depending on the relative strengths of the acid and base. The pH of such solutions can be predicted using the acid dissociation constants (Ka) of the parent acid and the parent base.

  2. F- as an example:

    • HF is a weak acid, so F- is its conjugate base. When F- is in solution, it can accept a proton from water to form HF and OH-. Since HF is a weak acid, F- is a weak conjugate base. However, the term “weak” can sometimes be misleading. F- is one of the stronger weak bases.
    • When F- reacts with Na+ to form NaF, NaF is a salt. When NaF dissolves in water, it dissociates into Na+ and F-. The Na+ does not affect the pH, but F- can accept a proton from water, making the solution basic.

  3. Regarding the rate constants for strong acids like HCl:

    • Technically, strong acids such as HCl are considered to dissociate completely in water, and thus, in theory, they do not have an equilibrium constant (or Ka). However, the term “completely” is a bit misleading. Even strong acids do not dissociate to 100%, but the extent of their dissociation is so high (typically greater than 90% or even 99%) that for most practical purposes, they can be considered to dissociate completely.
    • The reported Ka values for strong acids are often extrapolated or determined under specific conditions and can be very large numbers. They’re not typically used in calculations because, for practical purposes, strong acids are assumed to dissociate completely in dilute solutions.
    • In very concentrated solutions, even strong acids like HCl might not dissociate completely. In such cases, equilibrium considerations might become relevant.
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