Treating Complex Acid-Base Systems Complex systems are defined as solutions made up of: 1) Two acids or bases of different strengths HCl + CH3COOH NaOH + CH3COO2) An acid or base that has two or more acidic protons or basic functional groups H3PO4 Ca(OH)2 .3) An amphiprotic substance that is capable of acting as both acid and base HCO3- + H2O CO32- + H3O+ HCO3- + H2O H2CO3 + OHNH3+CH2COO- + H2O NH2CH2COO- + H3O+ NH3+CH2COO- + H2O NH3+CH2COOH + OH- .