Acids and BasesAcids and Bases

Topic 8General Properties

DefinitionspH Scale

Naming AcidsNaming Acids Binary Acids Only 2 elements Use “hydro-” prefix Change element ending

to “-ic” Add acid HCl – hydrochloric acid

Oxyacids 3 or more elements Use polyatomic name Change ending

– ate “-ic”– ite “-ous”

Add acid For S and P re-add

element ending– Sulfuric acid

CharacteristicsCharacteristics Acids

– Sour taste– Change color of indicators– React with metals to release

H2 gas– React with base to produce

salt and water– Conduct electric current– React with carbonates to

from CO2

Bases– Taste bitter– Change color of

indicators– Dilute solutions feel

slippery– React with base to

produce salt and water– Conduct electric

current

ArrheniusArrhenius

Acids– Produce H+ (H3O+)– Compounds usually

start with H HNO3 H+ + NO3

-

Bases– Produce OH-

– Compounds must contain OH

NaOH Na+ + OH-

Bronsted-LowryBronsted-Lowry

Acid– Donates protons (H+)

Base– Accepts protons (H+)

HClO + H2O H3O+ + ClO-

acid base acid base

The proton moves from HCl (donate) to H2O (accept).

HClO/ClO- would be an acid-base conjugate pair.

Acid-Base conjugate pairs differ by only a H+.

Lewis Acid/BaseLewis Acid/Base

Acid: electron pair acceptorBase: electron pair donatorFormation of a new covalent bond in which

both electrons are provided by one substance (dative covalent bonds).

Formation of complexes and complex ions are usually Lewis acid-base reactions

Lewis ExamplesLewis Examples• The Lewis definition is the broadest of the three acid

definitions. Generally the Lewis base has a lone pair of electrons for donating (H2O, NH3, CN-, OH- are all common examples.

• A bare proton (hydrogen ion) is a Lewis acid

H+(aq) + :NH3(aq) H:NH3+(aq) or NH4

+(aq)

• The silver ion can be a Lewis acidAg+(aq) + 2 :NH3(aq) [H3N:Ag:NH3]+(aq) or [Ag(NH3)2]+

Strong Acids and BasesStrong Acids and BasesMemorizeMemorize

Acids (7)– HCl– HBr– HI– HClO3

– HClO4

– HNO3

– H2SO4

Bases (7)– NaOH– KOH– RbOH– CsOH– Ca(OH)2

– Sr(OH)2

– Ba(OH)2

Strong (acid/base)Strong (acid/base)

The term strong relates to electrolytes.Strong acids and bases are strong

electrolytes: they conduct electricity.Strong just means that they dissociate or

ionize 100%

Neutraliztion ReactionsNeutraliztion Reactions

The products are generally a salt (ionic substance) and water.

Double replacement, hydrogen and the metal from the base switch anions.

Charge balance the salt then balance the reaction.

H2SO4 + Al(OH)3 Al2(SO4)3 + H2O

3H2SO4 + 2Al(OH)3 Al2(SO4)3 + 6H2O

pH ScalepH Scale pH is a measure of H+ or H3O+

pH from 0-7 acidic pH from 7-14 basic pH = 7 neutral Each unit change in pH represents a change of 10x

for hydronium ion concentration.

Brackets indicate concentration in moles per liter (M): [X] concentration of X.

Ions of InterestIons of Interest

Hydronium H3O+

Also just H+

Produced by acids

Hydroxide OH-

Produced by bases

[H3O+] x [OH-] = 1 x10-14 (@25C)

This allows you to determine the concentration of hydroxide or hydronium ion given one of the two. They are inversely

related via a constant.

pX = - log [X]pX = - log [X]

pH = - log [H+] pH = - log [H3O+]

pOH = - log [OH-]

pH + pOH = 14 (always)

This allows you to determine the pH or pOH given one of the two. The sum always equal 14.

‘‘Strehl Square’Strehl Square’

Strong acid/base pHStrong acid/base pH

‘Strong’ substances dissociate completelyWrite out the dissociation of the acid or

base.The concentration will be based upon the

starting concentration and the coefficient.For monoprotic and monohydroxides the

coefficient is 1.

Strong ExampleStrong Example

2.5M HCl– HCl H+ + Cl-

– 2.5M HCl 2.5M H+

0.5M Ca(OH)2

– Ca(OH)2 Ca2+ + 2OH-

– 0.5M Ca(OH)2 1.0M OH-

TitrationTitration

Determination of an unknown concentration by careful quantitative addition of a known solution (with a buret).

An indicator is used that will change color near the equivalence point where moles of H+ are equal to moles of OH-.

It is important to write the balanced neutralization reaction before any calculations.

Titration CalculationsTitration Calculations At the end of the titration the moles of hydronium

and hydroxide are equal. Molarity (M) = moles/volume We can find the moles of know by taking the

Mknown x volumeknown to get moles. We can then use the balanced reaction to convert

to moles of unknown. Finally by dividing by the volume of the unknown

we determine the concentration of the unknown.

Titration ExampleTitration Example 15.00mL of Sr(OH)2 were neutralized via titration

with 13.5mL of 2.00M HNO3. What is the concentration of Sr(OH)2

Sr(OH)2 + 2HNO3 Sr(NO3)2 + 2H2O 13.5mL = 0.0135L; 0.0135L x 2.00M = 0.0270

moles HNO3

0.0270 moles HNO3 x 1Sr(OH)2/2HNO3 = 0.0135 mole Sr(OH)2

M = 0.0135 mole/0.015L = 0.90M Sr(OH)2