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Acids and Bases

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Properties of Acids Produce H+ (as H3O+) ions in water (the hydronium ion

is a hydrogen ion attached to a water molecule)

Taste sour

Corrode metals

Good Electrolytes

React with bases to form a salt and water

pH is less than 7

Turns blue litmus paper to red “Blue to Red A-CID”

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Properties of Bases Generally produce OHGenerally produce OH-- ions in water ions in water

Taste bitter, chalkyTaste bitter, chalky

Are electrolytesAre electrolytes

Feel soapy, slipperyFeel soapy, slippery

React with acids to form salts and waterReact with acids to form salts and water

pH greater than 7pH greater than 7

Turns red litmus paper to blueTurns red litmus paper to blue “ “BBasicasic BBluelue””

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Naming AcidsBinary Acid – An acid that contains only two

elements, one of which is hydrogen and one which is more electronegative.

• HF – Hydrofluoric acid• HCl – Hydrochloric acid

Oxyacid – An acid that has hydrogen, oxygen, and a third element that is usually a non-metal•HClO4 – Perchloric acid•HNO2 – Nitrous acid•H2CO3 – Carbonic acid

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Arrhenius DefinitionAcid - Substances in water that increase

the concentration of hydrogen ions (H+).

Base - Substances in water that increase concentration of hydroxide ions (OH-).

Problem – many bases do not actually contain hydroxides

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Bronsted-Lowry Definition

Acid - neutral molecule, anion, or cation that donates a proton.

Base - neutral molecule, anion, or cation that accepts a proton.

HA + :B HB+ + :A-

HCl + H2O H3O+ + Cl-

Acid Base Conj Acid Conj Base

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Conjugate Base - The species remaining after an acid has transferred its proton.

Conjugate Acid - The species produced after base has accepted a proton.

HA & :A- - conjugate acid/base pair

:A- - conjugate base of acid HA

:B & HB+ - conjugate acid/base pair

HB+ - conjugate acid of base :B

Conjugate Acid Base Pairs

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Note: Water can act as acid or base

Acid Base Conjugate Acid Conjugate Base

HCl + H2O H3O+ + Cl-

H2PO4- + H2O

H3O+ + HPO4

2-

NH4+ + H2O

H3O+ + NH3

Base Acid Conjugate Acid Conjugate Base :NH3 + H2O

NH4+ + OH-

PO43- + H2O

HPO42- + OH-

Examples of Bronsted-Lowry Acid Base Systems

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Diprotic and Triprotic Acids (Polyprotic)

Sulfuric Acid can donate two protons per molecule

Phosphoric acid can donate three protons per molecule

H3PO4 + H2O H3O+ + H2PO4-

H2PO4- +H2O H3O+ + HPO4

2-

HPO42- +H2O H3O+ + PO4

3-

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Lewis

Acid - an electron pair acceptor

Base - an electron pair donor

G.N. Lewis Definition

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Common Strong Acids/Bases

Strong BasesStrong BasesSodium Hydroxide

Potassium Hydroxide

*Barium Hydroxide

*Calcium Hydroxide

*While strong bases they are not very soluble

Strong AcidsStrong AcidsHydrochloric Acid

Nitric Acid

Sulfuric Acid

Perchloric Acid

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Acid Strength

Strong Acid Weak Acid

Transfers all of its protons to water

Transfers only a small fraction of its protons to water

Completely Ionized Partly Ionized

Strong Electrolyte Weak Electrolyte

Conjugate Base is Weaker Conjugate Base is Stronger

As acid strength decreases, base strength increasesThe stronger the acid, the weaker its conjugate baseThe weaker the acid, the stronger its conjugate base

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Base Strength

Strong Base Weak Base

All molecules accept a protonFraction of molecules accept a

proton

Completely Ionized Partly Ionized

Strong Electrolyte Weak Electrolyte

Conjugate Acid is Weaker Conjugate Acid is Stronger

As base strength decreases, acid strength increasesThe stronger the base, the weaker its conjugate acidThe weaker the base, the stronger its conjugate acid

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Salts & Neutralization A salt is the neutralization product of an acid and

a base. The anion comes from the acid and the cation

from the base. Examples

HCl + NaOH NaCl + H2O.

H2SO4 + 2 KOH K2SO4 + H2O.

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The pH Scale

pH [H3O+ ] [OH- ] pOH

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pH and acidity

1. Acidity or Acid Strength depends on Hydronium Ion Concentration [H3O+]

2. The pH system is a logarithmic representation of the Hydrogen Ion concentration (or OH-) as a means of avoiding using large numbers and powers.

pH = - log [H3O+]

pOH = - log [OH-]

3. What is the pH of a solution if the [H3O+] is 3.4 x 10-5 M?

pH = -log [H3O+]

= -log(3.4 x 10-5)

= 4.47

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pH and acidity

Kw = [H3O+] [OH-] = 1.0 x10-14

In pure water

[H3O+] = [OH-] = 1.0 x10-7

pH + pOH = 14

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Indicators

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pH and acidity

The pH values of several common substances are shown at the right.

Many common foods are weak acids

Some medicines and many household cleaners are bases.