ACIDS AND BASES

Chapters 19 and 9.4

Acids and Bases

• Properties of ACIDS

Taste Sour/Tart

Stings and burns the skin

Reacts with bases

Turns blue litmus paper red

Reacts with metals to form H2

gas

Neutralizes Bases

Donates H+

Conduct electricity.

• Can be strong or weak electrolytes in aqueous solution

• Properties of BASES

Taste Bitter

Feels slippery on skin

Reacts with acids

Turns red litmus blue

Doesn’t react with metals

Neutralizes Acids

Accepts H+

Two important classification of compounds - Acids and Bases

Chapters 19 and 9.4

Acids Affect Indicators

Blue litmus paper turns red in

contact with an acid.

Chapters 19 and 9.4

Acids React with Active Metals

Acids react with active metals to

form salts and hydrogen gas:

HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)

Chapters 19 and 9.4

Sulfuric Acid – H2SO4

Highest volume production

of any chemical in the U.S.

Used in the production of

paper

Used in production of

fertilizers

Used in petroleum refining

Chapters 19 and 9.4

Nitric Acid – HNO3

• Used in the production of

fertilizers

• Used in the production of

explosives

• Nitric acid is a volatile acid –

its reactive components

evaporate easily

• Stains proteins (including

skin!)

Chapters 19 and 9.4

Hydrochloric Acid - HCl

• Used in the “pickling” of

steel

• Used to purify magnesium

from sea water

• Part of gastric juice, it aids

in the digestion of proteins

• Sold commercially as

“Muriatic acid”

Chapters 19 and 9.4

Phosphoric Acid – H3PO4

o A flavoring agent in sodas

o Used in the manufacture

of detergents

o Used in the manufacture

of fertilizers

o Not a common laboratory

reagent

Chapters 19 and 9.4

Acetic Acid – HC2H3O2

Used in the manufacture of

plastics

Used in making

pharmaceuticals

Acetic acid is the acid present in

household vinegar

Chapters 19 and 9.4

Bases Affect Indicators

Red litmus paper

turns blue in contact

with a base.Phenolphthalein

turns purple in a

base.

Chapters 19 and 9.4

Examples of Bases

Sodium hydroxide (lye), NaOH

Potassium hydroxide, KOH

Magnesium hydroxide, Mg(OH)2

Calcium hydroxide (lime),

Ca(OH)2

Chapters 19 and 9.4

Bases Neutralize Acids

Milk of Magnesia contains

magnesium hydroxide,

Mg(OH)2, which neutralizes

stomach acid, HCl.

2 HCl + Mg(OH)2

MgCl2 + 2 H2O

Acid-Base Theories

Arrhenius

(1883)

Brønsted–Lowry (1923)

Lewis (1923-38)

HCl NaOH

NH3

BF3

H2O

H2SO4

AlI3

CO32-

• An acid is a substance that dissociates in water to

produce hydrogen ions (H+)

• Example: Hydrochloric Acid (HCl)

• A base is a substance that dissociates in water to

produce hydroxide ions (OH-)

• Example: Sodium Hydroxide (NaOH)

Arrhenius Definition of A & B

Chapters 19 and 9.4

What happens when placed in

water???

Chapters 19 and 9.4

Svante Arrhenius (1859-1927)

Chapters 19 and 9.4

Brønsted-Lowry Definition

• An acid is any substance that can donate H+

ions.

• A base is any substance that can accept H+

ions.

• Expansion on Arrhenius definition of A&B

Defines A&B as not necessarily in water solution

Does not contain OH-; covers bases such as ammonia NH

3

Chapters 19 and 9.4

Johannes Bronsted Thomas Lowry

(1879-1947) (1874-1936)

Brønsted-Lowry Definition

• H+

is really only just a proton (no electrons or

neutrons), so definition is often in terms of protons

Brønsted-Lowry Base is a proton acceptor

Brønsted-Lowry Acid is a proton donor• Monoprotic Acids can only donate 1 H

+: HCl

• Diprotic Acids can donate 2 H+: H

2SO

4

• Triprotic Acids can donate 3 H+: H

3PO

4

• Polyprotic acids = diprotic and triprotic acids

Chapters 19 and 9.4

Chapters 19 and 9.4

Chapters 19 and 9.4

• Acid-base reactions with water proceed in both

directions:

Example: NH3

(g) + H2O (l) NH

4

+(aq) + OH

-(aq)

• Acid loses H+

= conjugate base

Example: H2O (acid) loses its H

+, turning it into OH

-

(conjugate base)

• Base gains H+

= conjugate acid

Example: NH3

(base) gains an H+, turning it into NH

4

+

(conjugate acid)

Conjugate Acid-Base Pairs

Chapters 19 and 9.4

Acids and bases come in pairs

• A “conjugate base” is the remainder of the

original acid, after it donates it’s hydrogen

ion

• A “conjugate acid” is the particle formed

when the original base gains a hydrogen ion

• Indicators are weak acids or bases that have

a different color from their original acid and

base

Chapters 19 and 9.4

The Hydronium Ion

• Water can pick up a H+

ion to form a hydronium ion:

H+

+ H2O H

3O

+H

3O

+= hydronium ion

• With acids, water is a Brønsted-Lowry base (accepts

protons

Example: HCl (g) + H2O(l) H

3O

+(aq) + Cl

-(aq)

• With bases, water is a Brønsted-Lowry acid (donates

protons)

Example: NH3

(g) + H2O (l) NH

4

+(aq) + OH

-(aq)

• Compound that can act as either a proton donor or

acceptor = amphoteric

Lewis Acids and Bases

• Gilbert Lewis focused on the donation or

acceptance of a pair of electrons during a

reaction

• Lewis Acid - electron pair acceptor

• Lewis Base - electron pair donor

• Most general of all 3 definitions; acids don’t even need hydrogen!

Gilbert Lewis (1875-1946)

Chapters 19 and 9.4

Lewis Acids and Bases

• Lewis acid = accepts a pair of electrons during a

reaction

• Lewis base = donates a pair of electrons during a

reaction

• Covers acids and bases not covered by Brønsted-

Lowry definition

Type Acid Base

Arrhenius H+

producer OH-producer

Brønsted-Lowry H+

(proton) donor H+

acceptor

Lewis Electron-pair

acceptor

Electron-pair donor

Table 19.4, Pg. 592, Text

Chapters 19 and 9.4

The pH Scale

• pH is based on the concentration of the

hydronium ion in a solution

• Concentrations range from 100

M (strong) to 10-14

M (weak) of [H3O

+]

• pH ranges from 0 to 14

If [H30

+] concentration = 10

-2 M, pH = 2

If [H30

+] concentration = 10

-10 M, pH = 10

Water is 10-7

M, pH = 7

• pH of 0-6 = Acidic

• pH of 7 = Neutral

• pH of 8-14 = Basic

pH

…..defined as the negative base-10 logarithm of the

hydronium ion concentration.

pH = −log [H3O+]

Problem: Calculate pH when [H3O+] = 2.3 x 10-3 M

Problem: Calculate [H3O+] when pH = 2.3 ?

10x

log

antilog10^ -2.3

10x

logbase 10 log log - 2.3 * 10^- 3

For pure H2O: [1.0 10−7 ] = 7.0

= 2.64

= 5.0 * 10-3

pH and pOH Calculations

H+ OH-

pH pOH

[OH-] = 1 x 10-14

[H+]

[H+] = 1 x 10-14

[OH-]

pOH = 14 - pH

pH = 14 - pOH

pO

H =

-lo

g[O

H- ]

pH

= -

log[H

+]

[OH

- ] =

10

-pO

H

[H+]

= 1

0-p

H

Chapters 19 and 9.4

pH

These are

the pH

values for

several

common

substances.

pH + pOH = 14

pH and pOH equilibrium

in pure Water

−log [H3O+] + −log [OH−] = −log Kw

• In pure water,

[H3O+] [OH−] = Kw

• Because in pure water [H3O+] = [OH−],

Kw = [1.0 10−7 ] [1.0 10−7 ] = 1.0 10−14

pH + pOH = pKw

7 + 7 = 14

[1.0 10−7 ] [1.0 10−7 ] = 1.0 10−14

pH and pOH equilibrium

in Water to which

Acids & Bases are Added

Kw = [1.0 10−8 ] [1.0 10−6 ] = 1.0 10−14

pH + pOH = pKw

8 + 6 = 14

H2O(l) + H2O(l) H3O+(aq) + OH−(aq)

OH-Add base

[H3O+] [OH−]H2O

Kw = [1.0 10−7 ] [1.0 10−7 ] = 1.0 10−14

Chapters 19 and 9.4

Measuring pH

• Why measure pH?

Solutions we use –• swimming pools

• soil conditions for plants

• medical diagnosis

• soaps and shampoos, etc.

• Sometimes we can use indicators, other times we might need a pH meter

Chapters 19 and 9.4

Acid-Base Strength

• An acid or a base is considered strong if they

completely dissociate into ions (H+

and OH-) in

water

• Strong Acids

HCl and H2SO

4

• Strong Bases

Hydroxides, e.g. NaOH

• Conjugate acid-base pairs have an inverse relationship

(works for both acids and bases)

The stronger the acid, the weaker the conjugate base

The weaker the acid, the stronger the conjugate base

Strong Acids and Bases to

know

Chapters 19 and 9.4

Measuring pH with wide-range paper

1. Moisten indicator

strip with a few drops

of solution, by using a

stirring rod.

2.Compare the color

to the chart on the vial

– read the pH value.

Chapters 19 and 9.4

Acid-Base Indicators

• Although useful, there are limitations to indicators:

usually given for a certain temperature (25 oC), thus may change at different temperatures

what if the solution already has color, like paint?

the ability of the human eye to distinguish colors is limited

Chapters 19 and 9.4

Some of the

many pH

Indicators

and their

ranges

Chapters 19 and 9.4

Red Cabbage Juice as an indicator

• Red cabbage juice

mixed with

baking soda (left)

and with vinegar

(right).

On the top, a drop

of unmixed juice.

Chapters 19 and 9.4

Acid-Base Indicators

• A pH meter may give more definitive results

some are large, others portable

works by measuring the voltage between two electrodes; typically accurate to within 0.01 pH unit of the true pH

needs to be calibrated

Chapters 19 and 9.4

Acids Neutralize Bases

HCl + NaOH → NaCl + H2O

-Neutralization reactions

ALWAYS produce a salt and

water.

-Of course, it takes the right

proportion of acid and base

to produce a neutral salt

Acid Base Salt

Strong Strong Neutral

Strong Weak Acidic

Weak Strong Basic

Weak Weak Neutral,

basic, or

acidic

Acid-Base Properties of Salts

• Neutralization reaction =

reaction of an acid and a

base

• Acid + base react – form a

salt and water

• Type of salt depends on

reactants

Chapters 19 and 9.4

Chapters 19 and 9.4

Chapters 19 and 9.4

Buffers

• Buffers are solutions in which the pH

remains relatively constant, even when

small amounts of acid or base are added

made from a pair of chemicals: a weak

acid and one of it’s salts; or a weak

base and one of it’s salts

Chapters 19 and 9.4

Chapters 19 and 9.4

Acid rain

Chapters 19 and 9.4

Causes of emissions

Chapters 19 and 9.4

pH readings nationwide

Chapters 19 and 9.4

Acid rain effects limestone and Marble

Chapters 19 and 9.4

Effects of Acid Rain on Marble(calcium carbonate)

George Washington:

BEFORE

George Washington:

AFTER

Chapters 19 and 9.4

Naming Acids and Bases

• Naming Acids: Three Rules

1. Name of anion ends in –ide

Acid name begins with hydro-

Stem of anion has suffix –ic

2. Name of anion ends in –ite

Stem of anion has suffix –ous

3. Name of anion ends in –ate

Stem of anion has suffix –ic

All three end with the word “acid”

Naming Bases

Named just like ionic compounds – cation + anion

Chapters 19 and 9.4

Acid – Base Humor