Presentation is loading. Please wait.

Presentation is loading. Please wait.

Salt, Hydrolysis of Salts. SALT:Neutralization product of acid base reactions. Classification by their origin: 1.Arrhenius-type acid + base: NaOH + HCl.

Similar presentations


Presentation on theme: "Salt, Hydrolysis of Salts. SALT:Neutralization product of acid base reactions. Classification by their origin: 1.Arrhenius-type acid + base: NaOH + HCl."— Presentation transcript:

1 Salt, Hydrolysis of Salts

2 SALT:Neutralization product of acid base reactions. Classification by their origin: 1.Arrhenius-type acid + base: NaOH + HCl = NaCl + H 2 O 2.Brønsted-type base + acid: NH 3 + HCl = NH 4 Cl 3. 3.Lewis-type acid + base reaction: AgCl + 2NH 3 = [Ag(NH 3 ) 2 ]Cl

3 Classification by their composition: a)Normal (neutral) salts: Salts as results of a stoichiometric neutralization reaction: 2NaOH + H 2 SO 4 = Na 2 SO 4 + 2H 2 O 3KOH + H 3 PO 4 = K 3 PO 4 + 3H 2 O

4 Classification by their composition: b)Acid salts: Salts formed by an incomplete neutralization of a polybasic acid. KOH + H 3 PO 4 = KH 2 PO 4 + H 2 O 2KOH + H 3 PO 4 = K 2 HPO 4 + 2H 2 O NaOH + H 2 CO 3 = NaHCO 3 + H 2 O

5 Classification by their composition: c)Base salts are products of a partial neutralization of a polyvalent (polyacidic) base. Bi(OH) 3 + HNO 3 = Bi(OH) 2 NO 3 + H 2 O d) d)Mixed salts Salts formed in a reaction of a polyacidic base with two different acids (One cation, two different anions) Ca(OH) 2 + HCl + HOCl = CaCl(OCl) + 2H 2 O

6 e) e)Double salts: Composed of two different cations and one kind of anion K 2 SO 4 + Al 2 (SO 4 ) 3 = 2KAl(SO 4 ) 2 (alum) When dissolved, they dissociate into all of their ionic components: KAl(SO 4 ) 2 = K + + Al SO 4 2- or, e.g.: (NH 4 ) 2 Fe(SO 4 ) 2 (Mohr’s salt) When dissolved in water: (NH 4 ) 2 Fe(SO 4 ) 2 = 2NH Fe SO 4 2-

7 f) f)Complex salts are coordination compounds composed of a non-dissociable complex ion and a dissociable counterion Salt with a complex cation: [Ag(NH 3 ) 2 ]Cl diamminesilver(l) chloride when dissolved: [Ag(NH 3 ) 2 ]Cl = [Ag(NH 3 ) 2 ] + + Cl - Salt with a complex anion: Na 3 [Ag(S 2 O 3 ) 2 ] Sodium dithiosulphatoargentate (I) In aqueous solution: Na 3 [Ag(S 2 O 3 ) 2 ] = 3Na + + [Ag(S 2 O 3 ) 2 ] 3-

8 Hydrolysis of Salts Hydrolysis: an acid-base reaction between water and the ion(s) of the dissolved salt. Preliminary consideration: 1.Water is neutral and amphoteric: H 2 O  H + + OH Dissolved salts exist in ionized form: NaCl  Na + + Cl -

9 3. 3.If any of the ions in solution has acid-base character, it will affect the self-ionization equilibrium of the solvent. 4.Cations 4.Cations of strong bases have no acid-base character while those of weak bases are acidic. K + + H 2 O = N. R. NH H 2 O  NH 3 + H 3 O + 5.Anions 5.Anions of strong acids have no acid-base character while those of weak asids are bases. SO H 2 O = N. R. CN - + H 2 O  HCN + OH -

10 Qualitative Aspects 1.No hydrolysis: neutral 1.No hydrolysis: Salts of strong acids and strong bases are neutral in solution. (NaCl, K 2 SO 4, CaCl 2 ….) 2.Anion-hydrolysis: basic 2.Anion-hydrolysis: Salts of weak acids and strong bases are basic in solution. Dissolution: KCN  K + + CN - Hydrolysis: CN - + H 2 O  HCN + OH -

11 Qualitative Aspects 4.Cation-anion hydrolysis: 4.Cation-anion hydrolysis: Salts of weak acids and weak bases can be acidic, basic or neutral in solution, owing to the hydrolysis of both ions. The reaction depends on relative acid-base strengths. Dissolution: NH 4 CN  NH CN - Cation-Hydrolysis: NH H 2 O  NH 3 + H 3 O + Anion-hydrolysis: CN - + H 2 O  HCN + OH - 3.Cation-hydrolysis: acidic 3.Cation-hydrolysis: Salts of strong acids and weak bases are acidic in solution. Dissolution: NH 4 Cl  NH Cl - Hydrolysis: NH H 2 O  NH 3 + H 3 O +

12 Quantitative Aspects Two equilibria coexist in aqueous solutions of hydrolyzable salts. 1.Self ionization of water: H 2 O  H + + OH - Kw = [H + ] [OH - ] 2.Hydrolysis of a cation (C + ) or an anion (A - ) a) C + + H 2 O  COH + H + K h(cation) = [COH] [H + ] [C + ] [COH] K w [C + ] [OH - ] = = KwKw KbKb [H + ] = K h [C + ]and pH = - log K h [C + ]

13 Quantitative Aspects 2.Hydrolysis of a cation (C + ) or an anion (A - ) b) A - + H 2 O  HA + OH - [OH - ] = K h [A - ]and pH = 14- pOH K h(anion) = [HA] [OH - ] [A - ] [HA] K w [A - ] [H + ] = = KwKw KaKa


Download ppt "Salt, Hydrolysis of Salts. SALT:Neutralization product of acid base reactions. Classification by their origin: 1.Arrhenius-type acid + base: NaOH + HCl."

Similar presentations


Ads by Google