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Acid-Base Properties of Salt Solutions

Acid-Base Properties of Salt Solutions. Salts That Form Neutral Solutions. Salts that contain a cation from a strong base AND an anion from a strong acid. e.g. NaCl & Ca(NO 3 ) 2. Salts That Form Acidic Solutions. Salts that contain a metal cation (excluding those in Groups 1 & 2) OR

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Acid-Base Properties of Salt Solutions

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  1. Acid-Base Properties of Salt Solutions Salts That Form Neutral Solutions Salts that contain a cation from a strong base AND an anion from a strong acid. e.g. NaCl & Ca(NO3)2

  2. Salts That Form Acidic Solutions Salts that contain a metal cation (excluding those in Groups 1 & 2) OR a cation that is the conjugate acid of a weak base AND the anion from a strong acid. e.g. NH4Cl & Fe(NO3)3

  3. Salts That Form Basic Solutions Salts that contain a cation from a strong base AND an anion that is the conjugate base of a weak acid. e.g. NaC2H3O2 & Mg(HCO3)2

  4. Hydrolysis The reaction of an ion with water to produce an acidic or basic solution. NH3(aq) + H3O+(aq) e.g. NH4+(aq) + H2O (l) acidic e.g. C2H3O2-(aq) + H2O (l) HC2H3O2(aq) + OH-(aq) basic

  5. What Happens if a Salt Has an Acidic Cation and a Basic Cation? e.g. Fe(C2H3O2)3 Ka for Fe3+ = 1.5 X 10-3 Kb for C2H3O2- = 5.6 X 10-10 Since Ka > Kb, A solution of Fe(C2H3O2)3 would be acidic.

  6. What Happens if a Salt Contains an Amphoteric Ion? An amphoteric ion can hydrolyze as an acid OR a base. e.g. HCO3-, H2PO4-, HPO42-, HSO4-, etc. If the Ka for the ion is > its Kb, the ion will act as an acid. e.g. For HSO4-, the Ka is 1.0 X 10-2 and its Kb is 1.0 X 10-12. Therefore, this ion will hydrolyze as an acid in water. HSO4-(aq) + H2O (l) SO42-(aq) + H3O+(aq) If the Kb for the ion is > its Ka, the ion will act as an acid. e.g. For HCO3- , the Ka is 4.7 X 10 -11 and its Kb is 2.1 X 10 -4. Therefore, this ion will act as a base in water: HCO3-(aq) + H2O (l) H2CO3(aq) + OH-(aq)

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