Question

How can I find out if something is a strong or weak acid or strong or weak base?

Answer 1

by finding its pH, or acidity. The higher the number the less acidic. 7 is neither an acid or a base.

Answer 2

^ this is so wrong

Answer 3

Uh oh D: What's the correct answer? I got my questions wrong and would like a correction.

Answer 4

There are several ways to define acidity and basicity, the most common is the Bronsted-Lowry, which deals in terms of H+ donation and acceptance.

Acids donate H+ into solution and make H3O+, hence they reduce the pH of a solution.

Bases accept H+ from solution and make more OH- and in turn decrease the H+, hence they increase the pH.

pH is just a measure of how much hydronium (H3O+) there is in solution, this is typically simplified as H+ although, it's incorrect as H+ does not exist on it's own.

pH = -log[H+]

so in terms of strength of an acid or a base, it depends on how stable the ion produced is.
This depends on the electronegativity of the atom/ion and resonance and the inductive effect. You should google these or search them on youtube.

Strong acids fully dissociate, e.g. HCl -> Cl- + H+
Strong bases also fully dissociate. e.g. KOH -> K+ + OH-


Weak Acids partially dissociate and thus an equilibrium is established:
e.g. CH3OH <-> CH3O- + H+
weak acids then have a dissociation constant, Ka, while strong acids don't because they fully dissociate and there is no equilibrium.

Similarly, for weak bases, they partially dissociate

NH3 + H2O <-> NH4+ + OH-

(in this example ammonia is picking up a proton from water and increasing [OH-])

these also have dissociation constants, Kb. In contrast, Strong bases fully dissociate thus there is no equilibrium, hence there is no Kb.


The most important part to determine the strength of an acid or a base is to look at it's conjugate acid or base, and determine it's stability (how "happy" it is being that ion)
for that you really have to look into resonance and the inductive effect. Look them up on youtube or goggle. It would take me too long to explain this with words, but if you have a specific question don't hesitate to ask, there are a lot of people on this site that can answer them.