How to know if it is a weak acid or base

Question

anonymous · Answer

A weak acid has a pH of between 5 and below 7, while a strong acid has a pH of 4 and below.

anonymous · Answer

Such an acid dissociates only partially in water, resulting in a low concentration of hydrogen ions, hence the pH level.

aaronq · Answer

"Such an acid dissociates only partially in water, resulting in a low concentration of hydrogen ions, hence the pH level." 

^this isn't true because the acidity of a solution (pH) is influenced by the concentration of the acid aswell. Just like dilute HCl has a pH close to 7, yet HCl is still considered a strong acid.

To find the strength (the extent of dissociation) of an acid you have to look it's the stability conjugate base.  $HA + H_2O\rightleftharpoons H_3O^+ + \underbrace{A^-}$
                                                         conjugate base

the conjugate base of HCl, $Cl^-$ is very stable as an anion (high electronegativity, filled orbitals), while the conjugate base of say, acetic acid, $CH_3COO^-$ is not as stable.