HA Acids, Bases and Salts H Acid-Base Theory The pH … · 2009-04-24 · Acids, Bases and Salts Acid-Base Theory ... Acid dissociation constant, Ka ... phenolphthalein methyl red

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HH++ + A + A--

9 - 1©1997, West Educational Publishing.

Acids, Bases and SaltsAcids, Bases and Salts

Acid-Base TheoryAcid-Base Theory

Self-Ionization of WaterSelf-Ionization of Water

Properties of Acids and BasesProperties of Acids and Bases

The pH ConceptThe pH Concept

Strengths of Acids and BasesStrengths of Acids and Bases

Analysis of Acids and BasesAnalysis of Acids and Bases

BuffersBuffers

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Acids and basesAcids and bases

A very important class of chemicals.

• Control CO 2 transport in the blood(buffers)

• Amino acids building blocks of protein(contain both and acid and a base)

• Acids are one of the 4 things we can taste(sour)

• Bases feel slippery

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Acids and basesAcids and bases

AcidicAcidic BasicBasic

Citrus fruits Baking sodaAspirin DetergentsCoca Cola Ammonia cleanersVinegar Tums and RolaidsVitamin C Soap

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Properties of acidsProperties of acids

• Sour taste.

• Produce H 3O+ when dissolved in water.

• Undergo double replacement reactions withsolid oxides, hydroxides, carbonates andbicarbonates.

HCl + NaOH NaCl + H2O

2 HCl + CaCO3 CaCl2 + CO2 + H2O

HCl + NaHCO3 NaCl + CO2 + H2O

2 HCl + CuO CuCl 2 + H2O

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Properties of acidsProperties of acids

Another property is the ability to react withmetals, producing hydrogen gas.

Zn + 2 HCl ZnCl 2 + H2

Some metals react better with acids thanothers.

We can show the reactivity using an

activity seriesactivity series

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Activity series of metalsActivity series of metals

potassiumsodium

potassiumsodium

calciumcalcium

magnesiumaluminum

zincchromium

magnesiumaluminum

zincchromium

ironnickel

tinlead

ironnickel

tinlead

coppersilver

platinumgold

coppersilver

platinumgold

incr

easi

ng r

eact

ivity

Reacts violently with cold water

Reacts slowly with cold water

Reacts very slowly with steambut quite reactive in acid

Reacts moderately with highlevels of acid

Unreactive in acid

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Activity series of metals -Activity series of metals -various metals invarious metals in HCl HCl

Iron Zinc Magnesium

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Properties of basesProperties of bases

• Solutions have a slippery or soapy feel.• Will react with acids to produce a salt.

Neutralization reactionNeutralization reaction

NaOH + HCl NaCl + H2O

Neutralization of fatty acids in the skinproduce soap. This is why bases feelslippery.

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SaltsSalts

When acids and bases react, they form waterand a salt.

KOH + HNO3 KNO3 + H2O (salt)

Salts are typically crystalline, ionic materials.

Most ionic compounds can actually beconsidered salts.

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Acid and Base StrengthAcid and Base Strength

Strong acidsStrong acids dissociate completely in water HCl, HBr, HI, HClO 3, HNO3, HClO4, H2SO4.

Weak acids Weak acids partially dissociate in water most acids are weak.

Strong basesStrong bases dissociate completely in water NaOH, LiOH, KOH

strong bases are metal hydroxides.

Weak basesWeak bases partially dissociate in water.

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DissociationDissociation

Strong acids and basesStrong acids and bases• considered to dissociate completely.

HCl(aq) + H2O(l) H3O+ (aq) + Cl-(aq)

NaOH(aq) + H2O(l) Na+(aq) + OH-

(aq)

Weak acids and basesWeak acids and bases• do not dissociate completely.

HC2H3O2 (aq) + H2O(l) H3O+(aq) +C2H3O2

-(aq)

NH3 (aq) + H2O(l) NH4+ (aq)+ OH-

(aq)

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Acid dissociation constant,Acid dissociation constant, K Kaa

The strength of a weak acid can be expressedas an equilibrium.

HA (aq) + H2O(l) H3O+(aq) + A-

(aq)

The strength of a weak acid is related to itsequilibrium constant, K a.

Ka = [A -][H3O+] [HA]

We omit water.It’s alreadyincluded in

the constant.

We omit water.It’s alreadyincluded in

the constant.

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Dissociation of bases,Dissociation of bases,KKbb

The strength of a weak base can also beexpressed as an equilibrium.

B (aq) + H2O(l) BH+(aq) +OH-

(aq)

The strength of a weak base is related to itsequilibrium constant, K b.

Kb = [OH-][BH +] [B]

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KKaa and K and K bb values values

For weak acids and bases

Ka and K b always have values that aresmaller than one.

• Acids with a larger K a are stronger thanones with a smaller K a.

• Bases witha larger K b are stronger thanones with a smaller K b.

Most acids and bases are considered weak.

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pH andpH and pOH pOH

We need to measure and use acids and basesover a very large concentration range.

pH and pOH are systems to keep track ofthese very large ranges.

pH = -log[H 3O+]pOH = -log[OH -]

pH + pOH = 14

LogarithmsLogarithms

As with exponents, this is a way of workingwith very large and very small numbers

log n• the abbreviation for the term logarithm• n is the base

log 10common logs

• based on 10• the only type we will be using• the 10 is usually omitted

We will only be using base 10 logs

©1997, West Educational Publishing. 9 - 22


For ‘whole’ numbers, the common log and theexponent in scientific notation are the same.

log(1000) = 3 1000 = 10 3

logs of other numbers are no integers but theidea is the same.

log(1500) = 3.176 1500 = 10 3.176



A positive log represents a number greaterthan one.

log(13456) = 4.1289

A negative log represents a number smallerthan one.

log(0.00291) = -2.54

You CAN’T take the log of a negative value.

log( -235 ) = error


LogarithmsLogarithms value log(value) 1000 3.0 500 2.7 100 2.0 50 1.7 10 1.0 5 0.7 1 0.0 0.5 -0.3 0.1 -1.0 0.05 -1.3 0.01 -2.0 0.005 -2.3 0.001 -3.0

The sign tells us if the number is larger or smaller than one.

The number before the decimal point tells us where the decimal point would be in scientific notation.

The number after the decimal point tells us what the number is.


Log practiceLog practice

Determine the following with your calculator:

log(12345) 4.1 <-- rounded off

log(1.5x10 5) 5.2

log(0.00005) -4.3

log(2.4x10 -6) -5.6


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pH calculationspH calculations

Determine the following. pH = -log[H +]

pH of 6.7x10 -3 M H+

= 2.2

pH of 5.2x10 -12 M H+

= 11.2

[H+], if the pH is 4.5 = 3.2x10-5 M H+

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pOHpOH examples examples

Determine the following. pOH = -log[OH -] = 14 - pH

pOH of 1.7x10 -4 M NaOH pOH = 3.8 pH = 10.2

pOH of 5.2x10 -12 M H+

pH = 11.2 pOH = 2.8

[OH-] , if the pH is 4.5 pOH = 9.5 [OH-] = 3.2x10-10 M

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pH scalepH scale

A log based scale used to keep track of thelarge change important to acids and bases.

14 7 0

10-14 M 10-7 M 1 MVery Neutral VeryBasic Acidic

When you add an acid, the pH gets smaller.

When you add a base, the pH gets larger.

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pH of somepH of somecommon materialscommon materials

Substance pH

1 M HCl 0.0

Lemon juice 2.3

Coffee 5.0

Pure Water 7.0

Blood 7.35-7.45

Milk of Magnesia 10.5

1M NaOH 14.0

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NeutralizationNeutralization

The reaction of an acid with a base to producea salt and water.

HCl + NaOH NaCl + H2O

We do this when we use antacids.

Neutralization can be used to determine theamount of acid or base in a sample.

-- titrations titrations

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Indicator examplesIndicator examples

Acid-base indicators are weak acids thatundergo a color change at a known pH.

bromthymol blue

phenolphthalein methyl red

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TitrationsTitrations

Analytical methods based on measurment ofvolume.

• If the concentration of an acid is known, theconcentration of the base can be found.

• If we know the concentration of the base,then we can determine the amount of acid.

• All that is needed is some calibratedglassware and either an indicator or pHmeter.

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TItrationsTItrations

BuretBuret - volumetric glasware used for titrations.

It allows you to add a known amount of your titrant to the solution you are testing.

If a pH meter is used, the equivalence point can be measured.

An indicator will give you the endpoint.

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BuffersBuffers

Solutions that resist change to pH when smallamounts of acid or base are added

Two typesTwo types• weak acid and it’s salt• weak base and it’s salt

HA(aq) + H2O(l) H3O+(aq) + A-

(aq)

Add OH - Add H +

shift to right shift to left

Based on LeChatelier’s Principle.

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Buffers and bloodBuffers and blood

Control of blood pHControl of blood pH

• Oxygen is transported primarily byhemoglobin in the red blood cells.

• CO2 transported both in plasma and thered blood cells.

CO2 (aq) + 2 H2O H2CO3 (aq)

H3O+(aq) + HCO3

-(aq)

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Buffers and bloodBuffers and blood

The amount of CO 2 helps control blood pH.

Too much COToo much CO 22 - Respiratory arrestpH goes down, acid level goes up.acidosisacidosisSolutionSolution - ventilate and give bicarbonate

via IV.

Too little COToo little CO 22 - Hyperventilation, anxietypH goes up, acid level goes down.alkalosisalkalosisSolutionSolution - rebreath CO 2 in paper bag to

raise level.

Documents

HA Acids, Bases and Salts H Acid-Base Theory The pH … · 2009-04-24 · Acids, Bases and Salts Acid-Base Theory ... Acid dissociation constant, Ka ... phenolphthalein methyl red