AcidsLesson 5

Acid Rain & Hydrolysis

Normal Rain has pH = 6 due to dissolved CO2

CO2 + H2O → H2CO3

Acid Rain

Acid Rain is caused by acid anhydrides

NO2 N2O4 automobile pollution

coal & smelter pollutionSO3SO2

SO3 + H2O → H2SO4(aq) Acid Rain has pH < 5

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

HCl → NaCl + HOH

strong acid strong base neutral salt

NaCl Consider the acid and base that makes NaCl

1. Neutral Salts

+ NaOH

→ Na+ + Cl-NaCl

Hydrolysis of Salts

→ NaCN + HOHHCN

weak acid strong base basic salt

Consider NaCN

+ NaOH

2. Basic Salts

→ Na+ + CN-

A basic salt will first dissociate in water

CN- ⇄ HCN + OH-

Hydrolysis

neutral base- negative ions are bases

NaCN

+ H2O

Cross off all bold ions- they do not hydrolyze and are neutral

Neutral

Acidic

Hydrolysis of Salts  3. Acidic Salts  

→ NH4 +

+ Cl- HCl

strong acid weak base acid salt

NH4Cl

+ NH3

positive ions are acids

NH4Cl → NH4+ + Cl- positive ion- acid

neutralacid

NH4+ ⇄ H3O+

Hydrolysis

+ NH3+ H2O

Cross off all bold ions- they do not hydrolyze and are neutral

Remaining amphriprotic ions are acidic

Neutral

Acidic

Basic

NH3 is a weak base

  4. Acidic Salts

acid saltweak basestrong acid

→ FeCl3 + 3HOH 3HCl

FeCl3

+ Fe(OH)3

Fe3+

OH-

H2O

H2O

H2O

H2O

H2O

H2O

Fe3+

OH-

H2O

H2O

H2O

H2O

H2O

Hydronium ion

FeCl3

Fe(H2O)63+ ⇄ H+ + Fe(H2O)5(OH)2+

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

Look for the reaction on the acid chart!

→ Fe3+ + 3Cl-