1. IX.Salts and Hydrolysis  Salts are simply ionic compounds.  Salts can be formed by: 1.A metal reacting with a non-metal. 2 Na (s) + Cl 2(g)  2 NaCl (s) 2.An acid reacting with a base. KOH (aq) + HCl (aq)  H 2 O (l) + KCl (aq) 3.An acid reacting with a metal. Mg (s) + 2 HCl (aq)  H 2(g) + MgCl 2(aq)  Salts often include polyatomic ions: eg: Na 3 PO 4 NH 4 Cl CaSO 4

2.  All salts are considered at least slightly soluble (recall K sp ) and many are highly soluble.  Many salts when dissolved in solution will change the pH of the solution – this is known as a hydrolysis reaction. eg: Na 2 CO 3 – sodium carbonate Na 2 CO 3(s)  2 Na + (aq) + CO 3 2 - (aq) dissociation first, then… CO 3 2- (aq) + H 2 O (l) HCO 3- (aq) + OH - (aq) Hydrolysis causes some OH - to be produced.  a solution of Na 2 CO 3 is actually basic.

3. eg: NH 4 Cl – ammonium chloride NH 4 Cl (s)  NH 4 + (aq) + Cl - (aq) then… NH 4 + (aq) + H 2 O (l) NH 3(aq) + H 3 O + (aq)  a solution of NH 4 Cl is actually acidic.

4. eg: NaHCO 3 – sodium bicarbonate NaHCO 3(s)  Na + (aq) + HCO 3 - (aq)  Does HCO 3 - act as an acid or a base? HCO 3 - (aq) + H 2 O (l) H 2 CO 3(aq) + OH - (aq)  a solution of NaHCO 3 is basic.  Compare K A with K B : K A = 5.6 x 10 -11 K B = 1.0 x 10 -14 4.3 x 10 -7 = 2.3 x 10 -8 K A (H 2 CO 3 )  HCO 3 - acts as a base.  In these examples notice that Na + and Cl - do not react with water. They have no H + to donate and no tendency to accept H + from H 2 O.

5. General Rules for Hydrolysis: 1.Cations (+ ions) of strong bases do not hydrolyze. eg: groups I & II metal ions (Na +, K +, Ca 2+ …) 2.Anions (- ions) of strong acids do not hydrolyze. eg: Cl -, Br -, ClO 4 -, NO 3 -, and I - 3.Any ion present on the K A table between strong acids & strong bases will hydrolyze.  If it has no H +, you know it will act as a base. eg:CO 3 2- (aq) + H 2 O (l) HCO 3- (aq) + OH - (aq)  If it has H +, it is amphiprotic and you must determine whether it acts as an acid or a base. (compare its K A to its K B ) Note:NH 4 + only acts as an acid. HSO 4 - only acts as an acid.