Acids, bases, strong and weak acids
Acids are proton (H+) donors.
As indicated above, water can act either as an acid or as a base. H3O+ and OH– are present in very low concentrations in pure water, due only to the reaction of water with itself.
Species referred to as acids are stronger than water as their reaction with water to produce H3O+ occurs to a greater extent than Reaction 1. Thus aqueous solutions of acids have a higher H3O+ concentration than pure water.
Species referred to as bases are stronger than water as their reaction with water to produce OH– occurs to a greater extent than Reaction 1. Thus aqueous solutions of bases have a higher OH– concentration than water.
Acids can be cations (NH4+) or molecules (CH3CO2H, H2O) or anions (H2PO42–).
Bases are proton (H+) acceptors.Bases can be either molecules (NH3, H2O) or anions (CH3CO2–).
As indicated above, water can act either as an acid or as a base. H3O+ and OH– are present in very low concentrations in pure water, due only to the reaction of water with itself.
Reaction 1: H2O + H2O 
H3O+ + OH–
means that conversion of reactants to products occurs to an extent of less than 100%.
H3O+ + OH– means that conversion of reactants to products occurs to an extent of less than 100%.Species referred to as acids are stronger than water as their reaction with water to produce H3O+ occurs to a greater extent than Reaction 1. Thus aqueous solutions of acids have a higher H3O+ concentration than pure water.
Reaction 2: 
Species referred to as bases are stronger than water as their reaction with water to produce OH– occurs to a greater extent than Reaction 1. Thus aqueous solutions of bases have a higher OH– concentration than water.
Reaction 3: 