ACIDS AND BASES

Properties of AcidsProperties of Acids

Acids taste sour Acids effect indicators

Blue litmus turns red Methyl orange turns red

Acids have a pH lower than 7 Acids are proton (hydrogen ion, H+) donors Acids react with active metals, produce H2

Acids react with carbonates Acids neutralize bases

Acids you must know:Acids you must know:

Strong Acids Weak Acids

Hydrochloric acid, HCl

Nitric acid, HNO3

Sulfuric acid, H2SO4 Phosphoric acid, H3PO4

Acetic acid, HC2H3O2

Properties of BasesProperties of Bases Bases taste bitter Bases effect indicators

Red litmus turns blue Phenolphthalein turns purple

Bases have a pH greater than 7 Bases are proton (hydrogen ion, H+) acceptors Solutions of bases feel slippery

Bases neutralize acids

Examples of BasesExamples of Bases

Sodium hydroxide (lye), NaOH Sodium hydroxide (lye), NaOH Potassium hydroxide, KOH Potassium hydroxide, KOH Magnesium hydroxide, Mg(OH)Magnesium hydroxide, Mg(OH)2 2

Calcium hydroxide (lime), Ca(OH)Calcium hydroxide (lime), Ca(OH)22

Arrhenius Acids and BasesAcids release hydrogen ions in water.Bases release hydroxide ions in water.

An acid is a substance that produces hydronium ions, H3O+, when dissolved in water.

Lewis DefinitionsA Lewis acid is a substance than can accept (and share) an electron pair.A Lewis base is a substance than can donate (and share) an electron pair.

Lewis acids

Lewis Acid

Bronsted-Lowry DefinitionsA Bronsted-Lowry acid is a proton donor; it donates a hydrogen ion, H+.A Bronsted-Lowry base is a proton acceptor; it accepts a hydrogen ion, H+.

Bronsted-Lowry

Arrheniusacids

Acid Definitions

Acid Definitions

Lewis acids

Bronsted-Lowry

Arrheniusacids

The Arrhenius model of acidsand bases was broadened bythe Bronsted-Lowry model.

The Lewis acid-base model isthe most general in scope.

The Lewis definition of an acidincludes any substance thatis an electron pair acceptor;a Lewis base is any substancethat can act as an electron pair donor.

Ralph A. Burns, Fundamentals of Chemistry 1999, page 483

Acid – Base Systems

Type Acid Base

Arrhenius H+ or H3O + producer

OH - producer

Bronsted-

Lowry

Proton (H +) donor

Proton (H +) acceptor

Lewis Electron-pair acceptor

Electron-pair donor

Acids are Proton DonorsAcids are Proton Donors

Monoprotic acidsDiprotic acids Triprotic acids

HCl

HC2H3O2

HNO3

H2SO4

H2CO3

H3PO4

Ionization of HCl and Ionization of HCl and formation of hydronium ion, formation of hydronium ion,

HH33OO++

H2O + HCl H3O+ + Cl-

Proton donor

Proton acceptor

Self-Ionization of WaterSelf-Ionization of Water

H2O + H2O H3O+ + OH-

Though pure water is considered a non-conductor, there is a slight, but measurable conductivity due to “self-ionization”

Ion Concentration in Ion Concentration in SolutionsSolutions

KKww – Ionization Constant for – Ionization Constant for WaterWater

In pure water at 25 C:

[H3O+] = 1 x 10-7 mol/L

[OH-] = 1 x 10-7 mol/L

Kw is a constant at 25 C:

Kw = [H3O+][OH-]

Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-

14

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 5 vs. pH 6 (10X more acidic)pH 3 vs. pH 5 (100X different)pH 8 vs. pH 13 (100,000X different)

: measures acidity/basicity

10x10x10x100x

H+, OH-, and pHH+, OH-, and pH

Calculating pH, Calculating pH, pOHpOHpH = -log10(H3O+)

pOH = -log10(OH-)

Relationship between pH and Relationship between pH and pOHpOH pH + pOH = 14

Finding [HFinding [H33OO++], [OH], [OH--] from pH, pOH] from pH, pOH

[H3O+] = 10-pH

[OH-] = 10-pOH

Strong Acids vs. Weak AcidsStrong Acids vs. Weak Acids

Strong acids are assumed to be 100% ionized in solution (good proton donors).

Weak acids are usually less than 5% ionized in solution (poor proton donors).

HCl

H2SO4 HNO3

H3PO4 HC2H3O2 Organic acids

Strong Acid DissociationStrong Acid Dissociation

Weak Acid DissociationWeak Acid Dissociation

Acids Effect IndicatorsAcids Effect Indicators

Blue litmus paper turns red in contact with an acid.

Acids Acids Have a pH Have a pH less than less than

77

Effects of Acid Rain on MarbleEffects of Acid Rain on Marble(calcium (calcium carbonatecarbonate))

George Washington: BEFORE

George Washington: AFTER

Bases Effect Bases Effect IndicatorsIndicators

Red litmus paper turns blue in contact with a base. Phenolphthale

in turns purple in a base.

Bases Bases have a pH have a pH

greater greater than 7than 7

Bases Neutralize Bases Neutralize AcidsAcids

Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl.

2 HCl + Mg(OH)2

MgCl2 + 2 H2O

Acids Neutralize BasesAcids Neutralize Bases

HCl + NaOH NaCl + H2O

Neutralization reactions ALWAYS produce a salt and water.

Neutralization

NeutralizationNeutralization is a chemical reaction between an acid and a base to produce a salt (an ionic compound) and water.

NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)base acid salt water

Some neutralization reactions:

H2SO4(aq) + NaOH(aq) Na2SO4 + HOH

sulfuric acid sodium hydroxide sodium sulfate water

HC2H3O2(aq) + Ca(OH)2(aq) Ca(C2H3O2)2 + HOH

acetic acid calcium hydroxide calcium acetate water

2 2

2 2

Neutralization

ACIDACID + BASE + 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

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

Salts

SaltsSalts - Ionic compounds containing a positive ion other than the hydrogen ion and a negative ion other than the hydroxide ion.

i.e., a metal and a non-metal

NaCl(s) + H2O(l) Na1+(aq) + Cl1-(aq)

Formulas and names of common salts

SALT FORMULA Common Name

sodium chloride NaCl (table) salt

sodium nitrate NaNO3 Chile saltpeter

sodium bicarbonate NaHCO3 baking soda

potassium carbonate K2CO3 potash

ammonium chloride NH4Cl sal ammoniac

NaCl