Acids and BasesSpecial kinds of aqueous solutions

“Ionization”

http://www.unit5.org/chemistry/AcidBase.html

Properties

electrolytes

turn litmus red

sour taste

react with metals to form H2 gas

slippery feel

turn litmus blue

bitter taste

ChemASAP

vinegar, milk, soda, apples, citrus fruits

ammonia, lye, antacid, baking soda

electrolytes

Common Acids

Sulfuric Acid H2SO4

Nitric Acid HNO3

Phosphoric Acid H3PO4

Hydrochloric Acid HCl

Acetic Acid CH3COOH

Carbonic Acid H2CO3

Battery acid

Used to make fertilizersand explosives

Food flavoring

Stomach acid

Vinegar

Carbonated water

Common Bases

Sodium hydroxide NaOH lye or caustic soda

Potassium hydroxide KOH caustic potash

Magnesium hydroxide Mg(OH)2 milk of magnesia

Calcium hydroxide Ca(OH) 2 slaked lime

Ammonia water NH3 H2O household ammonia

Name Formula Common Name

.NH4OH

NH41+ + OH1-

ammonium hydroxide

DefinitionsDefinitions

ArrheniusArrhenius - In aqueous solution… - In aqueous solution…

HCl + H2O H3O+ + Cl– •AcidsAcids form hydronium ions (H3O+)

H

HH H H

H

ClClO O

–+

acidCourtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

DefinitionsDefinitions

ArrheniusArrhenius - In aqueous solution… - In aqueous solution…

•BasesBases form hydroxide ions (OH-)

NH3 + H2O NH4+ + OH-

H

H

HH H

H

N NO O–+

H

H

H H

baseCourtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Definitions: Brønsted-Lowry

1+

+

hydronium ion

H3O+

1-

chloride ion

Cl-

(base)

H2O

(acid)

HCl

+ -

Acid = any substance that donates a proton.

Base = any substance that accepts a proton.

Definitions: Brønsted-Lowry

(acid)

H2O

(base)

NH3

+-1+

+

ammonium ion

NH4+

1-

hydroxide ion

OH-

Conjugate Acid-Base Pairs

HCl + H2O H3O+ + Cl-

acid base

base acid

conjugates

conjugates

HCl + H2O H3O+ + Cl-

acid base CA CB

Conjugate Acid-Base Pairs

NH3 + H2O NH41+ + OH-

base acid

acid base

conjugates

conjugates

base acid CA CB

NH3 + H2O NH41+ + OH-

Acid Strength

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 508

Strength(measured [H+] and [OH-])

Strong Acids/BasesStrong Acids/Bases– 100% ionized in water– strong electrolytes

- +

HCl

HNO3

H2SO4

HBr

HI

HClO3

HClO4

Group 1 Hydroxides

(plus Sr(OH)2, Ba(OH)2, and Ca(OH)2)

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Strength(measured [H+] and [OH-])

WeakWeak Acids/Bases Acids/Bases• do not ionize completely• weak electrolytes

- +

Examples:HF

CH3COOH

H3PO4

H2CO3

HCN

Example:

NH3

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

`

pH scale

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

ACID BASE

NEUTRAL

Each step on pH scale represents a factor of 10.

pH 6 to pH 5 (10X more acidic)pH 3 to pH 5 (100X less acidic)pH 8 to pH 13 (100,000X less acidic)

: measures acid/basic concentration

10x10x10x100x

Soren Sorensen(1868 - 1939)

pH Scale

Acid Base

0

7

14

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515

[H[H++] pH] pH

10-14 14

10-13 13

10-12 12

10-11 11

10-10 10

10-9 9

10-8 8

10-7 7

10-6 6

10-5 5

10-4 4

10-3 3

10-2 2

10-1 1

100 0

1 M NaOH

Ammonia(householdcleaner)

BloodPure waterMilk

VinegarLemon juiceStomach acid

1 M HCl

Aci

dic

N

eutr

al

Bas

ic

pH of Common Substance

14 1 x 10-14 1 x 10-0 0 13 1 x 10-13 1 x 10-1 1 12 1 x 10-12 1 x 10-2 2 11 1 x 10-11 1 x 10-3 3 10 1 x 10-10 1 x 10-4 4 9 1 x 10-9 1 x 10-5 5 8 1 x 10-8 1 x 10-6 6

6 1 x 10-6 1 x 10-8 8 5 1 x 10-5 1 x 10-9 9 4 1 x 10-4 1 x 10-10 10 3 1 x 10-3 1 x 10-11 11 2 1 x 10-2 1 x 10-12 12 1 1 x 10-1 1 x 10-13 13 0 1 x 100 1 x 10-14 14

NaOH, 0.1 MHousehold bleachHousehold ammonia

Lime waterMilk of magnesia

Borax

Baking sodaEgg white, seawaterHuman blood, tearsMilkSalivaRain

Black coffeeBananaTomatoesWineCola, vinegarLemon juice

Gastric juice

Mor

e ba

sic

Mor

e ac

idic

pH [H1+] [OH1-] pOH

7 1 x 10-7 1 x 10-7 7

[H+] [OH-] = 1 x 10-14 M (ionization constant of water (Kw))

pH = - log [H+] pOH = - log [OH-]

pH = 4.6

pH = - log [H+]

4.6 = - log [H+]

- 4.6 = log [H+]

- 4.6 = log [H+]

Given:

2nd log

10x

antilog

multiply both sides by -1

substitute pH value in equation

take antilog of both sides

Determine [H+]

choose proper equation

[H+] = 2.51x10-5 M

You can check your answer by working backwards.

pH = - log [H+]

pH = - log [2.51x10-5 M]

pH = 4.6

Recall, [H+] = [H3O+]

Litmus Paper

phenolphthalein colorless pinkacid baseweak strong

bromthymol blue yellow blue

acid basestrong strong

universal indicator R O Y G B I V

pH 4 7 12

Indicators

pH Paper

pH 0 1 2 3 4 5 6

pH 7 8 9 10 11 12 13

Acid-Base Neutralization

1+ 1-

+ +

Hydronium ion Hydroxide ion Water

H3O+ OH- H2O

Water

H2O

Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 584

NeutralizationNeutralization

ACID + BASE ACID + BASE SALT + WATER SALT + WATER

HCl + NaOH HCl + NaOH NaCl + H NaCl + H22OO

HCHC22HH33OO22 + NaOH + NaOH NaC NaC22HH33OO22 + H + H22OO

• Salts can be neutral, acidic, or basic.

• Neutralization does not mean pH = 7.

weak

strong strong

strong

neutral

basic

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100% Neutralization100% Neutralization

moles H3O+ = moles OH-

MV n = MV n

M: MolarityV: volumen: # of H+ ions in the acid

or OH- ions in the baseCourtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Equivalence point Equivalence point (endpoint)(endpoint)• Point at which equal amounts

of H3O+ and OH- are present.

• Determined by…

• indicator color change

TitrationTitration

• dramatic change in pH

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TitrationTitration

42.5 mL of 1.3M KOH are required to neutralize 50.0 mL of H2SO4. Find the molarity of H2SO4.

H3O+

M = ?V = 50.0 mLn = 2

OH-

M = 1.3MV = 42.5 mLn = 1

MVn = MVnM(50.0mL)(2)

=(1.3M)(42.5mL)(1)

M = 0.55M H2SO4

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Neutralization of Bug Bites

Wasp - stings with base

(neutralize with lemon juice or vinegar)

Red Ant - bites with acid

(neutralize with baking soda)

Range and Color Changes of SomeCommon Acid-Base Indicators

Indicators

pH Scale1 2 3 4 5 6 7 8 9 10 11 12 13 14

Methyl orange red 3.1 – 4.4 yellow

Methyl red red 4.4 6.2 yellow

Bromthymol blue yellow 6.2 7.6 blue

Neutral red red 6.8 8.0 yellow

Phenolphthalein colorless 8.0 10.0 red colorless beyond 13.0

Bromthymol blue indicator would be used in titrating a strong acid with a strong base.

Phenolpthalein indicator would be used in titrating a weak acid with a strong base.

Methyl orange indicator would be used in titrating a strong acid with a weak base.