AcidsLesson 6

Acid Rain & Hydrolysis

Acid Rain 

The cause of Acid Rain is the release of acid anhydrides into the environment.

Acid Anhydrides are nonmetal oxides.  NO2 N2O4 automobile pollution

 SO2 SO3 coal & smelter pollution

  SO3 + H2O → H2SO4(aq) Rain

  Acid Rain has pH < 5

Normal Rain has pH = 6 due to dissolved CO2

 CO2 + H2O → H2CO3

 Acid rain dissolves metal, limestone, concrete structures.  Acid rain decreases the pH of lakes and causes toxic metals to leach into them.

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  1. Neutral Salts Consider NaCl The neutralization equation used to produce NaCl will tell us what kind of salt it is. 

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  1. Neutral Salts Consider NaCl The neutralization equation used to produce NaCl will tell us what kind of salt it is. 

→ NaCl + HOH

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  1. Neutral Salts Consider NaCl The neutralization equation used to produce NaCl will tell us what kind of salt it is. 

H + OH → NaCl + HOH

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  1. Neutral Salts Consider NaCl The neutralization equation used to produce NaCl will tell us what kind of salt it is. 

HCl + NaOH → NaCl + HOH

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  1. Neutral Salts Consider NaCl The neutralization equation used to produce NaCl will tell us what kind of salt it is. 

HCl + NaOH → NaCl + HOH

strong acid strong base neutral salt

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  1. Neutral Salts Consider NaCl The neutralization equation used to produce NaCl will tell us what kind of salt it is. 

HCl + NaOH → NaCl + HOH

strong acid strong base neutral salt

When the acid and base parents are both strong the salt is always neutral. -

A neutral salt will dissociate in water.

NaCl → Na+ + Cl-

Cross off the both ions that come from strong parents as they do not hydrolyze or react further with water- they are neutral.

no ions to hydrolyze- neutral

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  2. Basic Salts Consider NaCN 

 

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  2. Basic Salts Consider NaCN 

 H + OH → NaCN + HOH

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  2. Basic Salts Consider NaCN 

 HCN + NaOH → NaCN + HOH

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  2. Basic Salts Consider NaCN 

 HCN + NaOH → NaCN + HOH

weak acid strong base basic salt

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  2. Basic Salts Consider NaCN 

 HCN + NaOH → NaCN + HOH

weak acid strong base basic salt

A basic salt will first dissociate in water

NaCN → Na+ + CN-

Cross off the Na+ because it has a strong parent and does not hydrolyze- it is neutral

Then the CN- ion, from the weak parent, will hydrolyze (react with water) as a Bronsted base.

CN- + H2O ⇄ HCN + OH-

negative ion left- basic

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  3. Acidic Salts Consider NH4Cl 

 → NH4Cl

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  3. Acidic Salts Consider NH4Cl 

 HCl + NH3 → NH4Cl

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  3. Acidic Salts Consider NH4Cl 

 HCl + NH3 → NH4Cl

strong acid weak base acid salt

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  3. Acidic Salts Consider NH4Cl 

 HCl + NH3 → NH4Cl

strong acid weak base acid salt

An acidic salt will first dissociate in water

NH4Cl → NH4+ + Cl-

Cross off the Cl- because it has a strong parent and does not hydrolyze- it is neutral

Then the NH4+ ion, from the weak parent, will hydrolyze (react with

water) as a Bronsted acid.

NH4+ + H2O ⇄ H3O+ + NH3

positive ion left- acidic

Hydrolysis of Salts Salts can be acidic, basic, or neutral.  4. Acidic Salts Consider FeCl3

  3HCl + Fe(OH)3 → FeCl3 + 3HOH

strong acid weak base acid salt

FeCl3 → Fe3+ + 3Cl-

The Fe3+ ion is an acid

Fe(H2O)63+ ⇄ H+ + Fe(H2O)5(OH)2+

You can copy these complex reactions right off the acid chart!

positive ion left- acidic