Hydrolysis of salts will be used to study the acid-base properties of dissolved ions in aqueous solutions. The approximate pH of these solutions will be determined using acid-base indicators. A buffer solution will be prepared, and its ability to moderate pH will be investigated alongside solutions that cannot function as buffers.
Brønsted-Lowry acids are proton donors and bases are proton acceptors. In water, an acid can donate a proton to water to form aqueous H + and the conjugate base; a base can accept a proton from water to form OH – and the conjugate acid. In acidic solutions, the concentration of H + (aq) is greater than the OH – concentration and the pH is less than 7, while the reverse is true in basic solutions ([H + ] – ], pH > 7). Aqueous solutions of substances such as HCl or HC2H3O2 are expected to be acidic, while aqueous solutions of substances such as NaOH or NH3 are expected to be basic. The dissolution of some salts into water can affect pH. For example, aqueous solutions of NaNO2 and KC2H3O2 are basic, whereas those of NH4Cl and FeCl3 are acidic. The dissolved ions have the potential to undergo proton transfer reactions with water to generate H + or OH – . Anions that are the conjugate bases of weak acids react with water to form OH – (aq). Cations that are the conjugate acids of weak bases can undergo a proton transfer reaction with water to generate H + (aq). Let HA represent a weak acid and A – its conjugate base. A weak acid is one which does not completely dissociate in or react with a water solution. Instead, equilibrium is established. The equilibrium constant is called the acid dissociation constant, Ka.
HA(aq) A – (aq) + H + (aq)A weak base is one which does not completely dissociate in or react with a water solution. Instead, equilibrium is established. The equilibrium constant is called the base dissociation constant, Kb.
