IX.Salts and Hydrolysis Salts are simply ionic compounds. Salts can be formed by: 1.A metal...

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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

Transcript of IX.Salts and Hydrolysis Salts are simply ionic compounds. Salts can be formed by: 1.A metal...

Page 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.

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) + Cl2(g) 2 NaCl(s)

2. An acid reacting with a base.KOH(aq) + HCl(aq) H2O(l) + KCl(aq)

3. An acid reacting with a metal.Mg(s) + 2 HCl(aq) H2(g) + MgCl2(aq)

Salts often include polyatomic ions:eg: Na3PO4 NH4Cl CaSO4

Page 2: 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.

All salts are considered at least slightly soluble (recall Ksp) 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: Na2CO3 – sodium carbonate

Na2CO3(s) 2 Na+(aq) + CO3

2-(aq)

dissociation first, then…

CO32-

(aq) + H2O(l) HCO3-(aq)

+ OH-(aq)

Hydrolysis causes some OH- to be produced.

a solution of Na2CO3 is actually basic.

Page 3: 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.

eg: NH4Cl – ammonium chloride

NH4Cl(s) NH4+

(aq) + Cl-(aq)

then…

NH4+

(aq) + H2O(l) NH3(aq) + H3O+

(aq)

a solution of NH4Cl is actually acidic.

Page 4: 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.

eg: NaHCO3 – sodium bicarbonate

NaHCO3(s) Na+(aq) + HCO3

-(aq)

Does HCO3- act as an acid or a base?

HCO3-(aq) + H2O(l) H2CO3(aq)

+ OH-(aq)

a solution of NaHCO3 is basic.

Compare KA with KB:

KA = 5.6 x 10-11 KB = 1.0 x 10-14

4.3 x 10-7 = 2.3 x 10-8

KA(H2CO3)

HCO3- 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 H2O.

Page 5: 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.

General Rules for Hydrolysis:

1. Cations (+ ions) of strong bases do not hydrolyze.eg: groups I & II metal ions (Na+, K+, Ca2+…)

2. Anions (- ions) of strong acids do not hydrolyze.eg: Cl-, Br-, ClO4

-, NO3-, and I-

3. Any ion present on the KA table between strong acids & strong bases will hydrolyze. If it has no H+, you know it will act as a base.

eg: CO32-

(aq) + H2O(l) HCO3-(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 KA to its KB)

Note: NH4+ only acts as an acid.

HSO4- only acts as an acid.