HA Acids, Bases and Salts H Acid-Base Theory The pH … · 2009-04-24 · Acids, Bases and Salts...
Transcript of HA Acids, Bases and Salts H Acid-Base Theory The pH … · 2009-04-24 · Acids, Bases and Salts...
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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
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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
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LogarithmsLogarithms
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
©1997, West Educational Publishing. 9 - 23
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LogarithmsLogarithms
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
©1997, West Educational Publishing. 9 - 24
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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.
©1997, West Educational Publishing. 9 - 25
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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
©1997, West Educational Publishing. 9 - 29
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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.