AcidsLesson 5

Acid Rain & Hydrolysis

Acid Rain

Acid Rain is caused by acid anhydrides

NO2 N2O4 automobile pollution

coal & smelter pollutionSO3SO2

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

HCl → 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

1. Neutral Salts

+ NaOH

→ Na+ + Cl-

A neutral salt will dissociate in water

Cross off ions from strong parents that are neutral.

NaCl

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

Neutral

Acidic

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

Remaining amphriprotic ions are acidic

Neutral

Acidic

Basic

→ Na+ + Cl-

A neutral salt will dissociate in water

no ions to hydrolyze- neutral

Cross off ions from strong parents that are neutral.

NaCl

Hydrolysis of Salts

→ NaCN + HOHHCN

weak acid strong base basic salt

Consider NaCN Consider the acid and base that makes NaCN

+ NaOH

2. Basic Salts

basic

→ Na+ + CN-

A basic salt will first dissociate in water

CN- ⇄ HCN + OH-

Hydrolysis

neutral base- negative ions are bases

NaCN

+ H2O

Hydrolysis of Salts  3. Acidic Salts  

→ NH4Cl HCl

strong acid weak base acid salt

NH4Cl

+ NH3

NH3 is a weak base

NH4Cl → NH4+ + Cl- positive ion- acid

neutralacid

NH4+ ⇄ H3O+

Hydrolysis

+ NH3+ H2O

  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+

positive ion - acid

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-