What are weak and strong acids?

Question

Natalie Anton · Accepted Answer

The strength an acid relates to the following equilibrium (in water):
#HA + H_2O rightleftharpoons H_3O^+ + A^-# For a strong acid, the equilibrium lies (strongly!) to the right. #HX# # (X =Cl, Br, I), H_2SO_4, HClO_4# are all examples of such "strong" acids. You should practise writing the equilibrium with these strong acids. Weak acids are those acids for which the equilibrium lies to the left, the reactant side. These include #HF, H_3CO_2H, H_3PO_4, H_2S#. Do not be intimidated by #H_3O^+#, it is simply a water molecule with another #H^+# added (are mass and charge conserved; its formal name is the hydronium ion). In water, we conceive the acid species to be a cluster of water molecules (2 or 3 or 4 or 5) with an extra #H^+# associated. Regarding the response above, the portrayal, #HA rightleftharpoons H^+ + A^-#, is entirely equivalent and acceptable. To measure #H^+# or #H_3O^+# we use the parameter #pH#, short for pouvoir hydrogene, which is #-log_(10)[H^+]#.

Ellie Andrews · Answer

undefined Weak acids partially dissociate in water and do not completely ionize, while strong acids fully dissociate into ions when dissolved in water. Examples of weak acids include acetic acid (found in vinegar) and citric acid (found in citrus fruits), while examples of strong acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and nitric acid (HNO₃).