Chapter 19Chapter 19

Acids and BasesAcids and Bases

TEKSTEKS

(G) define acids and bases and distinguish between Arrhenius and Bronsted-Lowry definitions and predict products in acid base reactions that form water;

(H) understand and differentiate among acid-base reactions, precipitation reactions, and oxidation-reduction reactions;

(I) define pH and use the hydrogen or hydroxide ion concentrations to calculate the pH of a solution; and

Properties of Acids and Properties of Acids and BasesBases

AcidsAcids Tastes sourTastes sour reacts with metals to reacts with metals to

produce hydrogen gasproduce hydrogen gas Reacts with carbonates Reacts with carbonates

to produce carbon to produce carbon dioxidedioxide

conducts electricity so conducts electricity so are good electrolytesare good electrolytes

Turns blue litmus redTurns blue litmus red Has a pH between 0-6Has a pH between 0-6 Reacts with a base to Reacts with a base to

produce salt and produce salt and waterwater

BasesBases Tastes bitterTastes bitter SlipperySlippery conducts electricityconducts electricity Turns red litmus Turns red litmus

blueblue Reacts with an acid Reacts with an acid

to produce salt and to produce salt and waterwater

Has a pH above 7Has a pH above 7

Ions in SolutionIons in SolutionAcidic Solution Neutral

solutions Basic Solution

• contains more H+ ions than OH- ions

• H+ > OH-

• neither acidic or basic

• equal # of H+ and OH- ions

• H+ = OH-

• contains more OH- ions than H+ ions

• H+ < OH-

Arrhenius vs Bronstead-Arrhenius vs Bronstead-LowryLowry

an acid is a substance that ionizes to produce hydrogen ions in aqueous solution

States that an acid is a hydrogen-ion donor

a base dissociates to produce a hydroxide ion in aqueous solution

a base is a hydrogen-ion acceptor

Amphoteric SubstancesAmphoteric Substances

Amphoteric-Amphoteric- a substance that a substance that can act as both acids and basescan act as both acids and bases– Ex: WaterEx: Water

When HF dissolves in water, When HF dissolves in water, water acts as basewater acts as base

When NHWhen NH33 dissolves in water, dissolves in water, water acts as acid water acts as acid

Strong Acids vs Weak AcidsStrong Acids vs Weak Acids

–http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/ac/m2/s1/index.htm

19.2 Strengths of Acids19.2 Strengths of Acids

Strong Acids Weak Acids

acid that ionizes completely

acid that ionizes only partially in dilute aqueous solutions

Ex: HC2H3O2, H2CO3

Good conductors of electricity, makes great electrolytesEx: HCl, HNO3, H2SO4

Poor conductors of electricity

Reactions shown with

Reactions shown with >

Strong Base vs Weak BaseStrong Base vs Weak Base

–http://www.mhhe.com/physsci/chemistry/chang7/esp/folder_structure/ac/m2/s2/index.htm

19.2 Strengths of Bases19.2 Strengths of Bases

Strong Base Weak Base

dissociate completely into metal ions and hydroxide ions

Ex: NaOH, Ca(OH)2

ionizes only partially in dilute aqueous solutions to form conjugate acid of the base and hydroxide ion

Ex: CH3NH2

19.3 What is pH?19.3 What is pH?

Pure water contains equal Pure water contains equal numbers of Hnumbers of H++ and OH and OH-- ions ions

KKww = [H = [H++] [OH] [OH--]]

Use 1.0x10Use 1.0x10-14-14 M M for Kfor Kww

Ion Product Constant of Ion Product Constant of WaterWater

Ion Product Constant of Ion Product Constant of Water-Water- K Kww- the value of the - the value of the equilibrium constant for equilibrium constant for waterwater

At 298 K, KAt 298 K, Kw w is 1.0 x 10is 1.0 x 10-14-14

KKww = [H = [H++] [OH] [OH--]]

pHpH

pHpH- the negative logarithm of - the negative logarithm of the hydrogen ion the hydrogen ion concentrationconcentration

pH = -log [HpH = -log [H++] ]

Math CalculationsMath Calculations

pH + pOH = 14pH + pOH = 14 pH= -log(HpH= -log(H++)) pH when given pOH = 14- (-log OH)pH when given pOH = 14- (-log OH)

pH ScalepH Scale

pH below 7 is an acidpH below 7 is an acidpH above 7 is a basepH above 7 is a basepH = 7 is neutralpH = 7 is neutral

pH of Common Substances

Timberlake, Chemistry 7th Edition, page 335

pH ScalepH Scale

http://www.purchon.com/chemistry/http://www.purchon.com/chemistry/flash/ph.swfflash/ph.swf

19.4 Neutralization19.4 Neutralization

Neutralization Reaction-Neutralization Reaction- acid acid & base react to produce a salt & base react to produce a salt & water& water– a Double-Replacement a Double-Replacement

ReactionReactionSalt-Salt- an ionic compound an ionic compound

formed from the cation of a formed from the cation of a base & anion of an acidbase & anion of an acid

Acid-Base Indicator-Acid-Base Indicator- a a compound that changes color compound that changes color as it is placed in either an as it is placed in either an acid or baseacid or base

TitrationTitration

The process in which an acid-base The process in which an acid-base neutralization reaction is used to neutralization reaction is used to determine the concentration of a determine the concentration of a solution of unknown concentration.solution of unknown concentration.

End PointEnd Point

The point at which an indicator used The point at which an indicator used in a titration changes colorin a titration changes color

BuffersBuffers

A solution that resists changes in pH A solution that resists changes in pH when limited amounts of acids and when limited amounts of acids and bases are added.bases are added.