Acids and BasesAcids and BasesAll you ever wanted to All you ever wanted to

know, and more!know, and more!

DefinitionsDefinitions

Arrhenius Arrhenius acidacid – contains H – contains H++ and and ionizes in water.ionizes in water.

HCl + HHCl + H22O O H H

33OO+ + + Cl+ Cl--

hydronium ionhydronium ion - H - H++ ion attached to water ion attached to water

HH22OO + H+ H++ ↔↔ H H

33OO+ +

Properties of AcidsProperties of Acids Taste sourTaste sour ElectrolytesElectrolytes React with bases to form salt & React with bases to form salt &

waterwater ie – HCl + NaOH ie – HCl + NaOH

React with active metals to React with active metals to produce hydrogen gasproduce hydrogen gas ie – HBr + Na ie – HBr + Na

Polyprotic acidsPolyprotic acids

Polyprotic - Acids that have many Polyprotic - Acids that have many protons to donateprotons to donate

i.e. Hi.e. H33POPO44

Monoprotic – one proton like HClMonoprotic – one proton like HCl

Diprotic – two protons, like HDiprotic – two protons, like H22SOSO44

H’s come off one at a time and H’s come off one at a time and require separate reactions for each require separate reactions for each H.H.

exampleexample

HH22SOSO44 + H + H22O O HSO HSO44-- + H + H++ + +

HH22OO

HSOHSO44-- + H + H22O O SO SO44

-2-2 + H + H++ + H + H22OO

Review on Naming AcidsReview on Naming Acids

1.1. Binary Acids – Binary Acids – A.A. (2 elements, H and some (2 elements, H and some

nonmetal)nonmetal)

B.B. Hydro----icHydro----ic

2.2. Ternary Acids – Ternary Acids – A. (3 elements, H & polyatomic ion)A. (3 elements, H & polyatomic ion)

1.1. ““ate” ion - ___ic acidate” ion - ___ic acid

2.2. ““ite” ion - ___ous acid ite” ion - ___ous acid

Arrhenius Arrhenius basebase – contains – contains OHOH-- and ionizes in water. and ionizes in water.

NaOH + HNaOH + H22O O Na Na++ + OH + OH-- + +

HH22OO

Properties of BasesProperties of Bases

Taste bitterTaste bitterFeels slipperyFeels slipperyReacts with acid to form salt Reacts with acid to form salt

and waterand waterElectrolytesElectrolytes

BrBrǿǿnsted-Lowry modelnsted-Lowry model

Acid – proton donor Acid – proton donor Base – proton acceptorBase – proton acceptor

What proton? What proton?

HH++ ion, once the electron ion, once the electron is removedis removed

Conjugate acid-base pairsConjugate acid-base pairs

Two substances related to each Two substances related to each other by donating and accepting other by donating and accepting a single proton (Ha single proton (H++))

Equilibrium reactions – reactions Equilibrium reactions – reactions where the forward and reverse where the forward and reverse reactions can both occur. reactions can both occur. (between weak acids and bases)(between weak acids and bases)

exampleexample

HF + HHF + H22O O ↔ H↔ H

33OO++ + F + F--

acid base conjugate acid base conjugate conjugateconjugate

acid baseacid base

NHNH33 + H + H

22O ↔ NHO ↔ NH

44++ + OH + OH--

base acid conjugate conjugatebase acid conjugate conjugate acid baseacid base

Water – acid, base or Water – acid, base or neutral?neutral?

Pure water is neutral because Pure water is neutral because [H+] = [OH-]

Water can act like an acid or Water can act like an acid or base depending on what it’s base depending on what it’s mixed withmixed with

Substances that can behave as Substances that can behave as both acid and base are said to both acid and base are said to be be amphotericamphoteric..

Auto Ionization of WaterAuto Ionization of Water

In pure water, 2 out of every In pure water, 2 out of every billion molecules ionize billion molecules ionize according to this reaction:according to this reaction:

HOH HOH H H++ + OH + OH--

This yields a concentration in This yields a concentration in water of:water of:

[H[H++] = 1 x 10] = 1 x 10-7-7 M M

[OH[OH--] = 1 x 10] = 1 x 10-7 -7 MM

So, all aqueous solutions (water) have both H+ and OH- ions present and the

product, 1 x 10-14, is a constant. If you know [ ] of one you can calculate the

other!

[H+] [OH-] = 1 x 10 -14

constant

Ion ConcentrationsIon Concentrations[H[H++] [OH] [OH--] = 1 x 10] = 1 x 10-14-14

1.1. What are the ion concentrations What are the ion concentrations of a 0.000453M solution of HCl?of a 0.000453M solution of HCl?

2.2. What are the ion concentrations What are the ion concentrations of a 0.00250M solution of KOH?of a 0.00250M solution of KOH?

If….

[H+] > [OH-], solution is acidic

[H+] = [OH-], solution is neutral

[H+] < [OH-], solution is basic

pH ScalepH Scale

pH stands for pH stands for powerpower of of HydrogenHydrogen

The pH scale was developed as an easier method of expressing ion concentrations.

pH = -log[H+]

pH ScalepH Scale

00 acid acid 77 base base

1414

neutralneutral

[H3O+] [OH-] = 1 x 10-14

-

log [

H3O

+]

pH + pOH = 14

anti

log (

-pO

H)

anti

log (

-pH

)

-log [

OH

- ]

Strengths of Acids and Strengths of Acids and BasesBases Strength of acids and bases is Strength of acids and bases is

determined by how much they determined by how much they ionize (how much Hionize (how much H++ or OH or OH-- they they produce.)produce.)

Examples – Examples –

HCl HCl H H++ + Cl + Cl--

≈≈100%100%

Therefore, HCl is considered strongTherefore, HCl is considered strong..

H22S ↔ HH++ + HS + HS--

>90% <10%

H2S is considered a weak acid because not much H+ is produced

So, how do you know if an acid or base is strong or weak?

Most are weak, so memorize the strong acids and bases then assume everything else to be weak.

Strong AcidsStrong Acids

HCl, hydrochloric acid HCl, hydrochloric acid HBr, hydrobromic acidHBr, hydrobromic acidHI, hydroiodic acidHI, hydroiodic acidHH22SOSO44,, sulfuric acidsulfuric acidHClOHClO44,, perchloric acidperchloric acidHClOHClO33, chloric acid, chloric acidHNOHNO33, nitric acid, nitric acid

Strong BasesStrong BasesNaOH, sodium hydroxideNaOH, sodium hydroxideKOH, potassium hydroxideKOH, potassium hydroxideRbOH, rubidium hydroxideRbOH, rubidium hydroxideCsOH, cesium hydroxideCsOH, cesium hydroxideCa(OH)Ca(OH)22, calcium hydroxide, calcium hydroxide

Sr(OH)Sr(OH)22, strontium hydroxide, strontium hydroxide

Ba(OH)Ba(OH)22, barium hydroxide, barium hydroxide

Once we know that an acid or Once we know that an acid or base is weak, then what?base is weak, then what?

Weak acids and bases produce Weak acids and bases produce a solution containing a mixture a solution containing a mixture of molecules and ions. The of molecules and ions. The concentration of the ions is concentration of the ions is determined by using an determined by using an equilibriumequilibrium expressionexpression..

k =k = [products] [products]

[reactants][reactants]

(except pure solids and liquids)(except pure solids and liquids)

Where:Where:k = ionization constantk = ionization constant[ ] = concentration in [ ] = concentration in

MolarityMolarity

Equilibrium Expressions

exampleexample

HCHC22HH33OO22 + H + H22O(O(l l ) ) ↔↔ C C22HH33OO22-- + +

HH33OO++

KK = = [C [C

22HH

33OO

22--] [H] [H

33OO++]]

[HC[HC22HH

33OO

22]]

R I C ER I C E

R = REACTIONR = REACTION

I = INITIAL concentrationI = INITIAL concentration

C = CHANGE in concentrationC = CHANGE in concentration

E = EQUILIBRIUM concentrationE = EQUILIBRIUM concentration

Example…Example…

1. What are the ion 1. What are the ion concentrations of 0.5M HIO, concentrations of 0.5M HIO, kkaa = 2.3 x 10 = 2.3 x 10-11-11

2. What is the pH?2. What is the pH?

Equilibrium always favors the weaker

acid/base pair.

NeutralizationNeutralization

When a strong acid reacts When a strong acid reacts with a strong base to form a with a strong base to form a salt and water.salt and water.

Example:Example:2NaOH + H2NaOH + H22SOSO44 Na Na22SOSO44 + 2H + 2H22OO

Titration ProblemsTitration Problems

Titration – using a solution of Titration – using a solution of known concentration to known concentration to determine the concentration determine the concentration of an unknown solutionof an unknown solution

Standard solution – solution Standard solution – solution of known concentrationof known concentration

Equivalence Point – the point Equivalence Point – the point when there are equal molar when there are equal molar amounts of acid and baseamounts of acid and base

Indicator – substance that Indicator – substance that changes color as the pH changes color as the pH changes. Indicators are changes. Indicators are chosen to change at the chosen to change at the equivalence point, called the equivalence point, called the end pointend point..

exampleexampleIn a titration, 42.8 mL of a In a titration, 42.8 mL of a

standard solution of Ca(OH)standard solution of Ca(OH)22 is added to 20.5 mL sample is added to 20.5 mL sample of HCl. The concentration of of HCl. The concentration of the calcium hydroxide is 0.35 the calcium hydroxide is 0.35 M. What is the molarity of M. What is the molarity of the acid solution?the acid solution?

Steps for Solving Steps for Solving ProblemsProblems

MMaaVVaaH’s = MH’s = MbbVVbbOH’sOH’s