Chemistry II Laboratory
Hydrolysis of salts will be used to study the acid-base properties of dissolved ions in aqueous solutions. Theapproximate pH of these solutions will be determined using acid-base indicators. A buffer solution will be prepared, and its ability to control pH will be studied, along with solutions that cannot functionas buffers. So, this experiment will serve to understand conjugate acid-base pairs, equilibria of weak acids and bases and to perform calculations involving ionic equilibria.
Salts are theproducts formed in neutralization reactions of acids and bases. Brønsted-Lowry acids are proton donors and bases are proton acceptors. In water, an acid can donate a proton to water to form H3O+ and theconjugate base; a base can accept a proton from water to form OH- and the conjugate acid. Also, when an acid and base undergo a neutralization reaction, the products usually include water and a“salt”. For example,
HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)
The dissolution of some salts into water can affect the pH. Nearly all salts are strong electrolytes and exist as ions in aqueoussolutions and react with water to produce acidic or basic solutions; these reactions are called hydrolysis reactions. It is the dissolved ions that have the potential to undergo proton transfers withwater to generate H3O+ or OH-. A weak acid is one which does not completely dissociate in or react with the water solution. The anions of this weak acid react with water to some extent to acceptprotons and generate OH-. Thus causing the solution pH to be greater than 7. Since there’s no complete dissociation of the weak acid, equilibrium is established. The equilibrium constant is called theacid dissociation constant and is given the symbol, Ka.
For instance the dissociation constant for, HA(aq) + H2O(l) A-(aq) + H3O+(aq), in which HA represents a weak acid; A- stands for its...