HSC Chemistry – Acidic Environment R Slider

* The pH of a salt depends upon the relative strength of the ions that make up the salt * Very few salts are neutral * Salts completely dissociate into their ions when sufficiently dilute NaCl (s)  Na + (aq) + Cl - (aq) * It is possible for these ions to interact with water to produce H+ or OH- ions which results in acidic or alkaline solutions. These are known as hydrolysis reactions

* Neutral anions are formed from strong acids * Neutral cations are formed from strong bases * NaCl is a neutral salt because the ions that are formed derive from a strong acid and base * HCl + NaOH  NaCl + H 2 O * Both of the acid and base completely dissociate, so there is no tendency for these ions to undergo hydrolysis reactions.

These react with water to form hydroxide ions * H 2 CO 3 + 2NaOH  Na 2 CO 3 + H 2 O * Na 2 CO 3  2Na + + CO 3 2- * CO H 2 O  HCO 3- + OH - In the above reactions: * NaOH is a strong base so the Na + will not react with water to form hydrogen ions * Carbonic acid is weak, so the carbonate ion will react with water to a small extent to form OH- ions Basic anions are formed by weak acids

Acidic anions are formed from polyprotic acids * In order to be acidic, a salt anion must contain a donatable proton (H + ) HSO 4- + H 2 0  H 3 O + + SO 4 2- Note: not all polyprotic acid anions are acidic. HCO 3- and HPO 4 2- are basic

Acidic cations are formed by weak bases * Again, a donatable hydrogen must be available on the cation. NH 4+ + H 2 O  NH 3 + H 3 O + NH 4+ + H 2 O  NH 3 + H 3 O + The ammonium ion comes from the weak base, ammonia, so a hydrolysis reaction can occur to a small extent producing hydronium ions.

* Neutral anions are formed from strong acids * Neutral cations are formed from strong bases * Basic anions are formed from weak acids * Acidic anions are formed from polyprotic acids * Acidic cations are formed from weak bases