AcidsLesson 5

Acid Rain & Hydrolysis

Acid Rain 

Acid Rain is caused by acid anhydrides

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

1. Neutral Salts 

  HCl + NaOH → NaCl + HOH

strong acid strong base neutral salt

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

NaCl Consider the acid and base that makes NaCl

A neutral salt will dissociate in water.

NaCl → Na+ + Cl-

Cross off ions from strong parents that are neutral.

no ions hydrolyze- neutral

Hydrolysis of Salts 2. Basic Salts   

NaCN + HOHHCN + NaOH →

weak acid strong base basic salt

Consider NaCN Consider the acid and base that makes NaCN

A basic salt will first dissociate in water

NaCN → Na+ + CN-

Na+ neutral

CN- base.

CN- + H2O ⇄ HCN + OH-

Hydrolysis

Hydrolysis of Salts  3. Acidic Salts Consider NH4Cl 

→ NH4Cl HCl + NH3

strong acid weak base acid salt

NH4Cl → NH4+ + Cl- positive ion- acid

Cl- neutral

NH4+ acid

NH4+ + H2O ⇄ H3O+ + NH3

Hydrolysis

  4. Acidic Salts   

acid saltweak basestrong acid

→ FeCl3 + 3HOH 3HCl + Fe(OH)3

Consider FeCl3

Fe3+

OH-

H2O

H2O

H2O

H2O

H2O

H2O

Fe3+

OH-

H2O

H2O

H2O

H2O

H2O

H+

FeCl3 → Fe3+ + 3Cl-

Fe(H2O)63+ ⇄ H+ + Fe(H2O)5(OH)2+

Look for the reaction on the acid chart!

positive ion - acid

Hydrolysis- when the positive or negative ion in a salt reacts with water as an acid or base.