“acids, bases, and salts”. acids-bases n objectives: –define the properties of acids and bases

“Acids, Bases, and Salts”

Acids-BasesAcids-Bases OBJECTIVES:OBJECTIVES:

–Define the properties of acids and bases.

Acid-Base TheoriesAcid-Base Theories OBJECTIVES:OBJECTIVES:

–Compare and contrast acids and bases as defined by the theories of: a) Arrhenius, b) Brønsted-Lowry, and c) Lewis.

Acid-Base in the Real WorldAcid-Base in the Real World

AcidsAcids

How many foods can you think of that are sour?How many foods can you think of that are sour?

That sour taste is due to the acid contained That sour taste is due to the acid contained in the foodin the food..

ExamplesExamplesSour Milk –lactic acidSour Milk –lactic acid

Vinegar- acetic acidVinegar- acetic acid

Soda – phosphoric acidSoda – phosphoric acid

Lemons and oranges – citric acidLemons and oranges – citric acid

Grape juice – tartaric acidGrape juice – tartaric acid

Acid-Base in the Real WorldAcid-Base in the Real World

BasesBases

Many everyday items in the householdMany everyday items in the household contain bases.contain bases.

Cleaning products and simple medicines.Cleaning products and simple medicines.

ExamplesExamplesHousehold cleaners – ammonia Household cleaners – ammonia

Drain and oven cleaners- NaOHDrain and oven cleaners- NaOH

Antacids – magnesium hydroxide,Antacids – magnesium hydroxide,

aluminum hydroxide andaluminum hydroxide and

sodium bicarbonatesodium bicarbonate

Properties of AcidsProperties of Acids They taste They taste sour.sour. They can They can conduct electricityconduct electricity..

–Can be strong or weak electrolytes in aqueous solution

React with metalsReact with metals to form H to form H22 gas. gas. Change the colorChange the color of indicators of indicators

(for example: blue litmus turns to red).(for example: blue litmus turns to red). React with basesReact with bases (metallic hydroxides) (metallic hydroxides)

to form water and a salt.to form water and a salt.

Properties of AcidsProperties of Acids They have a They have a pH of less than 7pH of less than 7 (more (more

on this concept of pH in a later lesson)on this concept of pH in a later lesson) They They react with carbonates and react with carbonates and

bicarbonatesbicarbonates to produce a salt, water, to produce a salt, water, and carbon dioxide gasand carbon dioxide gas

How do you know if a chemical is an How do you know if a chemical is an acid?acid?– It usually starts with Hydrogen.

– HCl, H2SO4, HNO3, etc. (but not water!)

Acid NomenclatureAcid Nomenclature

A binary acid is an acid that contains A binary acid is an acid that contains only two different elements: hydrogen only two different elements: hydrogen and one of the more electronegative and one of the more electronegative elementselements..

HF – hydrofluoric acidHF – hydrofluoric acidHCl – hydrochloric acidHCl – hydrochloric acidHBr – hydrobromic acidHBr – hydrobromic acidHI – hydroiodic acidHI – hydroiodic acid

Acid NomenclatureAcid Nomenclature

A oxyacid is an acid that contains A oxyacid is an acid that contains Hydrogen, oxygen and a third element, Hydrogen, oxygen and a third element, usually a nonmetal.usually a nonmetal.

CHCH33COOH – acidic acidCOOH – acidic acid

HNOHNO33 – nitric acid – nitric acid

HH22SOSO44 – sulfuric acid – sulfuric acid

HH33POPO44 – phosphoric acid – phosphoric acid

Sulfuric AcidSulfuric Acid = H = H22SOSO44

Highest volume production of Highest volume production of anyany chemical in the U.S. chemical in the U.S. (approximately 60 billion (approximately 60 billion pounds/year)pounds/year)

Used in the production of paperUsed in the production of paper

Used in production of fertilizersUsed in production of fertilizers

Used in petroleum refining; auto Used in petroleum refining; auto batteriesbatteries

Nitric AcidNitric Acid = HNO = HNO33

Used in the production of fertilizerUsed in the production of fertilizer

Used in the production of explosivesUsed in the production of explosives

Nitric acid is a Nitric acid is a volatile volatile acid – its reactive acid – its reactive components evaporate easilycomponents evaporate easily

Stains proteins yellow (including skin!)Stains proteins yellow (including skin!)

Hydrochloric AcidHydrochloric Acid = HCl = HCl

Used in the “pickling” of steel (remove Used in the “pickling” of steel (remove surface impurities)surface impurities)

Used to purify magnesium from sea waterUsed to purify magnesium from sea water

Part of gastric juice, it aids in the Part of gastric juice, it aids in the digestion of proteinsdigestion of proteins

Sold commercially as Sold commercially as Muriatic acid Muriatic acid (cleaning bricks and masonary)(cleaning bricks and masonary)

Phosphoric AcidPhosphoric Acid = H = H33POPO44

A flavoring agent in sodas (adds “tart”)A flavoring agent in sodas (adds “tart”)

Used in the manufacture of detergentsUsed in the manufacture of detergents

Used in the manufacture of fertilizersUsed in the manufacture of fertilizers

NotNot a common laboratory reagent a common laboratory reagent

Acetic AcidAcetic Acid - - CHCH33COOHCOOH

Used in the manufacture of plasticsUsed in the manufacture of plastics

Used in making pharmaceuticalsUsed in making pharmaceuticals

Acetic acid is the acid that is present in Acetic acid is the acid that is present in household household vinegarvinegar

Acids Affect Indicators, by Acids Affect Indicators, by changing their colorchanging their color

Blue litmus paper turns red in contact with an acid (and red paper stays red).

Acids Acids have a have a

pH pH lessless

than 7than 7

Acids React with Active MetalsAcids React with Active Metals

Acids react with active metals to form salts and hydrogen gas:

HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)

This is a single-replacement reaction

Acids React with Carbonates Acids React with Carbonates and Bicarbonatesand Bicarbonates

HCl + NaHCO3

NaCl + H2O + CO2

Hydrochloric acid + sodium bicarbonate

salt + water + carbon dioxide

An old-time home remedy for relieving an upset

stomach

Effects of Effects of Acid RainAcid Rain on Marble on Marble(marble is calcium (marble is calcium carbonatecarbonate))

George Washington:BEFORE acid rain

George Washington:AFTER acid rain

Acids Acids NeutralizeNeutralize Bases BasesHCl + NaOH → NaCl + H2O

-Neutralization reactions ALWAYS produce a salt (which is an ionic compound) and water.

-Of course, it takes the right proportion of acid and base to produce a neutral salt

Properties of BasesProperties of Bases (metallic hydroxides)(metallic hydroxides)

React with acidsReact with acids to form water to form water and a salt.and a salt.

Taste Taste bitterbitter.. Feel slipperyFeel slippery (don’t try this either). (don’t try this either). Can be strong or weak Can be strong or weak

electrolyteselectrolytes in aqueous solution in aqueous solution Change the colorChange the color of indicators of indicators

(red litmus turns blue).(red litmus turns blue).

Examples of BasesExamples of Bases(metallic hydroxides)(metallic hydroxides)

Sodium hydroxide, Sodium hydroxide, NaOHNaOH (lye for (lye for drain cleaner; soap)drain cleaner; soap)

Potassium hydroxide, KOH Potassium hydroxide, KOH (alkaline (alkaline batteries)batteries)

Magnesium hydroxide, Mg(OH)Magnesium hydroxide, Mg(OH)22 (Milk (Milk

of Magnesia)of Magnesia)

Calcium hydroxide, Ca(OH)Calcium hydroxide, Ca(OH)22 (lime; (lime;

masonry)masonry)

Bases Affect IndicatorsBases Affect Indicators

Red litmus paper turns blue in contact with a base (and blue paper stays blue).

Phenolphthalein turns purple in a base.

Bases Bases have a have a

pH pH greatergreater than 7than 7

Bases Neutralize AcidsBases Neutralize Acids

Milk of Magnesia contains magnesium hydroxide, Mg(OH)2, which neutralizes stomach acid, HCl.

2 HCl + Mg(OH)2

MgCl2 + 2 H2O

Magnesium salts can cause diarrhea (thus they are used as a laxative) and may also cause kidney stones.

Acid-Base TheoriesAcid-Base Theories

Svante ArrheniusSvante Arrhenius He was a Swedish chemist (1859-He was a Swedish chemist (1859-

1927), and a Nobel prize winner in 1927), and a Nobel prize winner in chemistry (1903)chemistry (1903)

one of the first chemists to explain one of the first chemists to explain the chemical theory of the behavior the chemical theory of the behavior of acids and basesof acids and bases

Dr. Hubert Alyea (professor emeritus Dr. Hubert Alyea (professor emeritus at Princeton University) was the last at Princeton University) was the last graduate student of Arrhenius.graduate student of Arrhenius.

1. Arrhenius Definition - 18871. Arrhenius Definition - 1887 AcidsAcids produce hydrogen ions (H produce hydrogen ions (H1+1+) )

in in aqueous solutionaqueous solution (HCl (HCl → → HH1+1+ + Cl + Cl1-1-))

BasesBases produce hydroxide ions produce hydroxide ions (OH(OH1-1-) when dissolved ) when dissolved in waterin water..

(NaOH → Na1+ + OH1-) Limited to Limited to aqueous solutionsaqueous solutions.. Only one kind of base (hydroxides)Only one kind of base (hydroxides) NHNH33 (ammonia) could not be an (ammonia) could not be an

Arrhenius base: no OHArrhenius base: no OH1-1- produced. produced.

Svante Arrhenius (1859-1927)Svante Arrhenius (1859-1927)

Polyprotic Acids?Polyprotic Acids? Some compounds have Some compounds have more than more than

one ionizable hydrogenone ionizable hydrogen to release to release HNOHNO3 3 nitric acid - nitric acid - monomonoproticprotic

HH22SOSO44 sulfuric acid - sulfuric acid - didiprotic - 2 Hprotic - 2 H++

HH33POPO44 phosphoric acid - phosphoric acid - tritriprotic - 3 protic - 3

HH++

Having more than one ionizable Having more than one ionizable hydrogen does hydrogen does notnot mean stronger! mean stronger!

AcidsAcids Not all compounds that have Not all compounds that have

hydrogen are acids. Water?hydrogen are acids. Water? Also, not all the hydrogen in an Also, not all the hydrogen in an

acid may be released as ionsacid may be released as ions

–only those that have very polar bonds are ionizable - this is when the hydrogen is joined to a very electronegative element

Arrhenius examples...Arrhenius examples... Consider HCl = it is an acid!Consider HCl = it is an acid! What about CHWhat about CH44 (methane)? (methane)? CHCH33COOH (ethanoic acid, also COOH (ethanoic acid, also

called acetic acid) - it has 4 called acetic acid) - it has 4 hydrogens just like methane hydrogens just like methane does…?does…?

Organic AcidsOrganic Acids (those with carbon) (those with carbon)

Organic acids all contain the carboxyl group, (-COOH), sometimes several of them. CH3COOH – of the 4 hydrogen, only 1 ionizable

The carboxyl group is a poor proton donor, so ALL organic acids are weak acids.

(due to being bonded to the highly electronegative Oxygen)

2. Brønsted-Lowry - 19232. Brønsted-Lowry - 1923 A broader definition than ArrheniusA broader definition than Arrhenius AcidAcid is hydrogen-ion donor (H is hydrogen-ion donor (H+ + or or

proton); proton); basebase is hydrogen-ion acceptor. is hydrogen-ion acceptor. Acids and bases always come in pairs.Acids and bases always come in pairs. HCl is an acid.HCl is an acid.

– When it dissolves in water, it gives it’s proton to water.

HClHCl(g)(g) + H + H22OO(l)(l) ↔↔ H H33OO++(aq)(aq) + Cl + Cl--(aq)(aq)

Water is a base; makes hydronium ion.Water is a base; makes hydronium ion.

Johannes Brønsted Thomas LowryJohannes Brønsted Thomas Lowry (1879-1947) (1874-1936) (1879-1947) (1874-1936) Denmark Denmark England England

Why Ammonia is a BaseWhy Ammonia is a Base Ammonia can be explained as a Ammonia can be explained as a

base by using Brønsted-Lowry:base by using Brønsted-Lowry:

NHNH3(aq)3(aq) + H + H22OO(l)(l) ↔ NH↔ NH441+1+

(aq)(aq) + OH + OH1-1-(aq)(aq)

Ammonia is the hydrogen ion Ammonia is the hydrogen ion acceptor (acceptor (basebase), and water is the ), and water is the hydrogen ion donor (hydrogen ion donor (acidacid).).

This causes the OHThis causes the OH1-1- concentration concentration to be greater than in pure water, to be greater than in pure water, and the ammonia solution is and the ammonia solution is basicbasic

Acids and bases come in Acids and bases come in pairspairs A “A “conjugate baseconjugate base”” is the remainder of is the remainder of

the original acid, after it the original acid, after it donatesdonates it’s it’s hydrogen ionhydrogen ion

A “A “conjugate acidconjugate acid”” is the particle is the particle formed when the original base formed when the original base gainsgains a a hydrogen ionhydrogen ion

Thus, a conjugate acid-base pair is related by Thus, a conjugate acid-base pair is related by the the loss or gainloss or gain of a of a single hydrogen ionsingle hydrogen ion..

Acids and bases come in Acids and bases come in pairspairs General equation is: General equation is:

HAHA(aq)(aq) + H + H22OO(l)(l) ↔↔ H H33OO++(aq)(aq) + A + A--

(aq)(aq)

Acid + Base Acid + Base ↔↔ Conjugate acid + Conjugate base Conjugate acid + Conjugate base

NHNH33 + H + H22O O ↔↔ NH NH441+1+ + OH + OH1-1-

base base acidacid c.a. c.b. c.a. c.b. HCl + HHCl + H22O O ↔↔ H H33OO1+1+ + Cl+ Cl1-1-

acid acid basebase c.a. c.b. c.a. c.b. AmphotericAmphoteric – a substance that can – a substance that can act as act as

bothboth an acid and base- as water shows an acid and base- as water shows

3. Lewis Acids and Bases3. Lewis Acids and Bases Gilbert Lewis focused on the Gilbert Lewis focused on the

donation or acceptance of a pair of donation or acceptance of a pair of electrons during a reactionelectrons during a reaction

Lewis AcidLewis Acid - electron pair acceptor - electron pair acceptor Lewis BaseLewis Base - electron pair donor - electron pair donor Most general of all 3 definitions; Most general of all 3 definitions;

acids don’t even need hydrogen!acids don’t even need hydrogen! SummarySummary: Table 19.4, page 592: Table 19.4, page 592

Gilbert Lewis (1875-1946)Gilbert Lewis (1875-1946)

- Page 593

Hydrogen Ions and AcidityHydrogen Ions and Acidity

OBJECTIVES:OBJECTIVES:

–Describe how [H1+] and [OH1-] are related in an aqueous solution.



–Classify a solution as neutral, acidic, or basic given the hydrogen-ion or hydroxide-ion concentration.



–Convert hydrogen-ion concentrations into pH values and hydroxide-ion concentrations into pOH values.



–Describe the purpose of an acid-base indicator.

Hydrogen Ions from WaterHydrogen Ions from Water Water ionizes, or falls apart into ions:Water ionizes, or falls apart into ions:

2H2O ↔ 2H+ + 2OH-

Called the “Called the “self ionizationself ionization” of water” of water Occurs to a Occurs to a very smallvery small extent extent::

[H1+ ] = [OH1-] = 1 x 10-7 M Since they are equal, a Since they are equal, a neutralneutral solution solution

results from waterresults from water

KKww = [H = [H1+1+ ] x [OH ] x [OH1-1-] = 1 x 10] = 1 x 10-14-14 MM22

KKww is called the “ is called the “ionization constantionization constant” for water” for water

Ion Product ConstantIon Product Constant 2H2H22O O ↔↔ 2H 2H++ + 2OH + 2OH--

KKww is is constantconstant in every aqueous solution: in every aqueous solution:

[H[H++] x [OH] x [OH--] = ] = 1 x 101 x 10-14 -14 MM22

If [HIf [H++] > 10] > 10-7-7 then [OH then [OH--] < 10] < 10-7-7 If [HIf [H++] < 10] < 10-7-7 then [OH then [OH--] > 10] > 10-7-7

If we know one, other can be determinedIf we know one, other can be determined If [HIf [H++] > 10] > 10-7-7 , it is , it is acidicacidic and [OH and [OH--] < 10] < 10-7-7 If [HIf [H++] < 10] < 10-7-7 , it is , it is basicbasic and [OH and [OH--] > 10] > 10-7-7

– Basic solutions also called “alkaline”

Strong acids and bases are completely ionized in aqueous solutions:

HCl H+ + Cl-

NaOH Na+ + OH-

Therefore:

NaOH Na+ + OH-

1 mole 1 mole

1 x 10-2 M 1 x 10-2 M

This is a basic solution

ProblemsProblems

Calculating [HCalculating [H++] and [OH] and [OH--]]

The pH Scale – from 0 to 14The pH Scale – from 0 to 14 pH = pH = pouvoir hydrogenepouvoir hydrogene (Fr.) (Fr.)

“hydrogen power” “hydrogen power”

definition: definition: pH = -log[HpH = -log[H++]] in in neutralneutral pH = -log(1 x 10 pH = -log(1 x 10-7-7)) = 7 = 7 in in acidicacidic solution [H solution [H++] > 10] > 10-7 -7

pH pH < < -log(10-log(10-7-7))– pH < 7 (from 0 to 7 is the acid range)

– pH > 7 (7 to 14 is base range)

Calculating pOHCalculating pOH pOH = -log [OHpOH = -log [OH--] ] [H[H++] x [OH] x [OH--] = 1 x 10] = 1 x 10-14 -14 MM22

pH + pOH = 14pH + pOH = 14

Not greatly used like pH is.Not greatly used like pH is.

pH and Significant FigurespH and Significant Figures For pH calculations, the hydrogen For pH calculations, the hydrogen

ion concentration is usually ion concentration is usually expressed in scientific notationexpressed in scientific notation

[H[H1+1+] = 0.0010 M = 1.0 x 10] = 0.0010 M = 1.0 x 10-3-3 M, and M, and 0.000.001010 has 2 significant figures has 2 significant figures

the pH = 3.the pH = 3.0000, with the two , with the two numbers to the right of the decimal numbers to the right of the decimal corresponding to the two significant corresponding to the two significant figuresfigures

Problem 1Problem 1

What is the pH of a solution if the What is the pH of a solution if the [H[H33OO++] is 1 x 10] is 1 x 10-6-6 M? M?

pH = -log(1 x 10-6) = 6

The solution is acidic

pH = -log[HH33O+O+]

Problem 2Problem 2

What is the pH of a solution if the What is the pH of a solution if the [OH[OH--] is 1 x 10] is 1 x 10-2-2 M? M?

pH = -log[HH33O+O+]

[H[H++] x [OH] x [OH--] = 1 x 10] = 1 x 10-14 -14 MM22

[H[H++] x [1 x 10] x [1 x 10-2-2] = 1 x 10] = 1 x 10-14-14 MM22

[H[H++] = 1 x 10] = 1 x 10-12-12 MM

Problem 2Problem 2

What is the pH of a solution if the What is the pH of a solution if the [OH[OH--] is 1 x 10] is 1 x 10-2-2 M? M?

pH = -log(1 x 10-12) = 12

The solution is basic

pH = -log[HH33O+O+]

Problem 3Problem 3

What is the pH of a solution if What is the pH of a solution if the [Hthe [H33O+] is 3.4 x 10O+] is 3.4 x 10-5-5 M? M?

Hint: since 3.4 x 10Hint: since 3.4 x 10-5-5 M is M is between 10between 10-4-4 and 10 and 10-5-5 the pH of the pH of the solution must be between 4 the solution must be between 4 and 5.and 5.

Problem 3Problem 3What is the pH of a solution if What is the pH of a solution if the [Hthe [H33O+] is 3.4 x 10O+] is 3.4 x 10-5-5 M? M?

pH = -log[HH33O+O+]

pH = -log[3.4 x 103.4 x 10-5-5 ]

pH = 4.47

ProblemsProblems

1) What is the pH of a solution if 1) What is the pH of a solution if the [Hthe [H33O+] is 6.7 x 10O+] is 6.7 x 10-4-4 M? M?


ProblemsProblems1)1) What is the pH of a solution What is the pH of a solution

if the [Hif the [H33O+] is 6.7 x 10O+] is 6.7 x 10-4-4 M? M?

Answer: 3.17Answer: 3.17


Answer: 1.60Answer: 1.60

ProblemsProblems

3) Determine the pH of a 2.0 x 103) Determine the pH of a 2.0 x 10-2-2 M M Sr(OH)Sr(OH)22 solution. solution.

ProblemsProblems

3) Determine the pH of a 2.0 x 103) Determine the pH of a 2.0 x 10-2-2 M M Sr(OH)Sr(OH)22 solution. solution.

[OH[OH--] = 4.0 x 10] = 4.0 x 10-2-2 M M

[H+] = 2.5 x 10[H+] = 2.5 x 10-13-13 M M

pH = -log[2.5 x 10pH = -log[2.5 x 10-13-13] = 12.60] = 12.60

Measuring pHMeasuring pH Why measure pH?Why measure pH?

Everyday solutions we use - everything from swimming pools, soil conditions for plants, medical diagnosis, soaps and shampoos, etc.

Sometimes we can use Sometimes we can use indicatorsindicators, other times , other times we might need a we might need a pH pH metermeter

How to measure pH with wide-range paperHow to measure pH with wide-range paper

1. Moisten the pH indicator paper strip with a few drops of solution, by using a stirring rod.

2.Compare the color to the chart on the vial – then read the pH value.

Acid-Base IndicatorsAcid-Base IndicatorsCompounds whose colors are Compounds whose colors are sensitive to pH.sensitive to pH.

The color of the indicator changes The color of the indicator changes as the pH of a solution changes.as the pH of a solution changes.

Indicators are weak acids or basesIndicators are weak acids or bases

HHInIn H H++ + In + In-- ( (InIn-- anion part) anion part)

HHInIn H H++ + In + In--

Acid-Base IndicatorsAcid-Base Indicators

The color that the indicator The color that the indicator displays result from the fact that displays result from the fact that HIn and InHIn and In-- are different colors are different colors

HHInIn H H++ + In + In--

Pink BluePink Blue

Ex.Ex.

acidacid

basebase

Some of the Some of the many pH many pH

Indicators Indicators and theirand theirpH rangepH range

Acid-Base IndicatorsAcid-Base Indicators Although useful, there are Although useful, there are limitationslimitations

to indicators:to indicators:–usually given for a certain

temperature (25 oC), thus may change at different temperatures

–what if the solution already has a color, like paint?

– the ability of the human eye to distinguish colors is limited

Acid-Base IndicatorsAcid-Base Indicators A A pH meterpH meter may give more definitive may give more definitive

resultsresults–some are large, others portable–works by measuring the voltage

between two electrodes; typically accurate to within 0.01 pH unit of the true pH

–Instruments need to be calibrated

BuffersBuffers BuffersBuffers are solutions in which the are solutions in which the

pH remains relatively constant, pH remains relatively constant, even when small amounts of acid even when small amounts of acid or base are addedor base are added

made from a pair of chemicals: a weak acid and one of it’s salts

BuffersBuffers A buffer system is better able to A buffer system is better able to

resist changes in pH than pure waterresist changes in pH than pure water

Since it is a Since it is a pairpair of chemicals: of chemicals:–one chemical neutralizes any acid

added, while the other chemical would neutralize any additional base

BuffersBuffersExample: acetic acid in waterExample: acetic acid in water

CHCH33COOH CHCOOH CH33COOCOO-- + H + H++

The The buffer capacitybuffer capacity is the amount of acid or base is the amount of acid or base that can be added before a significant change in that can be added before a significant change in pHpH

Aspirin (which is a type of acid) sometimes causes stomach upset; thus by adding a “buffer”, it does not cause the acid irritation.

Bufferin is one brand of a buffered aspirin that is sold in stores.

Chapter 16Chapter 16Strengths of Acids and BasesStrengths of Acids and Bases OBJECTIVES:OBJECTIVES:

–Define strong acids and weak acids.


–Describe how an acid’s strength is related to the value of its acid dissociation constant.


–Calculate an acid dissociation constant (Ka) from concentration and pH measurements.


–Order acids by strength according to their acid dissociation constants (Ka).


–Order bases by strength according to their base dissociation constants (Kb).

StrengthStrength Acids and Bases are classified acording Acids and Bases are classified acording

to the degree to which they ionize in to the degree to which they ionize in water:water:– Strong are completely ionized in

aqueous solution; this means they ionize 100 %

– Weak ionize only slightly in aqueous solution

StrengthStrength is very different from is very different from ConcentrationConcentration

StrengthStrength Strong – means it forms Strong – means it forms manymany

ions when dissolved (100% ions when dissolved (100% ionization)ionization)

Mg(OH)Mg(OH)22 is a strong base- it falls is a strong base- it falls completely apart (nearly 100% completely apart (nearly 100% when dissolved). when dissolved). –But, not much dissolves- so it

is not concentrated

Strong Acid DissociationStrong Acid Dissociation (makes 100 % ions)(makes 100 % ions)

Weak Acid DissociationWeak Acid Dissociation(only partially ionizes)(only partially ionizes)

Measuring strengthMeasuring strength Ionization is reversible:Ionization is reversible:

HA + HHA + H22O O ↔↔ H H++ + A + A- -

This makes an equilibriumThis makes an equilibrium Acid dissociation constant = KAcid dissociation constant = Kaa

KKaa = [H = [H++ ][A ][A- - ] ]

[HA][HA] Stronger acidStronger acid = more products (ions), = more products (ions),

thus a thus a larger Klarger Kaa (Table 19.7, page 607) (Table 19.7, page 607)

(Note that water is NOT shown, because its concentration is constant, and built into Ka)

(Note that the arrow goes both directions.)

What about bases?What about bases? Strong bases dissociate completely.Strong bases dissociate completely.

MOH + HMOH + H22O O ↔↔ M M++ + OH + OH-- (M = a metal)(M = a metal)

Base dissociation constant = KBase dissociation constant = Kbb

KKbb = [M = [M++ ][OH ][OH--]]

[MOH] [MOH] Stronger baseStronger base = more dissociated = more dissociated

ions are produced, thus a ions are produced, thus a larger Klarger Kbb..

Strength vs. ConcentrationStrength vs. Concentration The words The words concentratedconcentrated and and dilutedilute tell tell

how much of an acid or base is how much of an acid or base is dissolved in solution - refers to the dissolved in solution - refers to the number of moles of acid or base in a number of moles of acid or base in a given volumegiven volume

The words The words strongstrong and and weakweak refer to the refer to the extent of ionization of an acid or baseextent of ionization of an acid or base

Is a Is a concentrated, weakconcentrated, weak acid possible? acid possible?

PracticePractice Write the KWrite the Kaa expression for HNO expression for HNO22

1) Equation: HNO2 ↔ H1+ + NO21-

2) Ka = [H1+] x [NO21-]

[HNO2]

Write the KWrite the Kbb expression for NH expression for NH3 3

(as NH(as NH44OH)OH)

- Page 610

Chapter 16Chapter 16Neutralization ReactionsNeutralization Reactions


–Define the products of an acid-base reaction.



–Explain how acid-base titration is used to calculate the concentration of an acid or a base.



–Explain the concept of equivalence in neutralization reactions.



–Describe the relationship between equivalence point and the end point of a titration.

Acid-Base ReactionsAcid-Base Reactions Acid + Base Water + SaltAcid + Base Water + Salt Properties related to every day:Properties related to every day:

–antacids depend on neutralization

–farmers adjust the soil pH

–Baking powder

–human body kidney stones from insoluble salts

Acid-Base ReactionsAcid-Base Reactions Neutralization ReactionNeutralization Reaction - a reaction - a reaction

in which an acid and a base react in in which an acid and a base react in an aqueous solution to produce a an aqueous solution to produce a salt and water:salt and water:

HClHCl(aq)(aq) + NaOH + NaOH(aq) (aq) NaClNaCl(aq)(aq) + H + H22OO(l)(l)

HH22SOSO4(aq)4(aq) + 2KOH + 2KOH(aq) (aq) K K22SOSO4(aq)4(aq) + 2 H + 2 H22OO(l)(l)

TitrationTitration TitrationTitration is the process of adding a is the process of adding a

known amount of solution of known known amount of solution of known concentration to determine the concentration to determine the concentration of another solutionconcentration of another solution

Remember - a Remember - a balanced equationbalanced equation is a is a mole ratiomole ratio

The The equivalence pointequivalence point is when the moles is when the moles of hydrogen ions is of hydrogen ions is equalequal to the moles to the moles of hydroxide ions (= neutralized!)of hydroxide ions (= neutralized!)

- Page 614

TitrationTitration The concentration of acid (or base) The concentration of acid (or base)

in solution can be determined by in solution can be determined by performing a neutralization reactionperforming a neutralization reaction

–An indicator is used to show when neutralization has occurred

–Often we use phenolphthalein- because it is colorless in neutral and acid; turns pink in base

Steps - Neutralization reactionSteps - Neutralization reaction

#1. A measured volume of acid of #1. A measured volume of acid of unknownunknown concentration is added to concentration is added to a flaska flask

#2. Several drops of indicator added#2. Several drops of indicator added

#3. A base of #3. A base of knownknown concentration is concentration is slowly added, until the indicator slowly added, until the indicator changes color; measure the volumechanges color; measure the volume

NeutralizationNeutralization The solution of known The solution of known

concentration is called the concentration is called the standard solutionstandard solution– added by using a buret

Continue adding until the Continue adding until the indicator indicator changes colorchanges color– called the “end point” of the titration

Problem 1Problem 1

Suppose 20.0 mL of 5.0 x 10Suppose 20.0 mL of 5.0 x 10-3-3M M NaOH is required to reach the end NaOH is required to reach the end point in the titration of 10.0 mL of point in the titration of 10.0 mL of HCl of unknown concentration. HCl of unknown concentration. Determine the molarity of HCl.Determine the molarity of HCl.

HClHCl(aq)(aq) + NaOH + NaOH(aq) (aq) NaClNaCl(aq)(aq) + H + H22OO(l)(l)

1 mole 1 mole1 mole 1 mole

known: 20 mL of 5.0 x 10known: 20 mL of 5.0 x 10-3-3 M NaOH M NaOH 10 mL of HCl10 mL of HClunknown: M of HClunknown: M of HCl

(0.005 M)(0.020 L) = (M HCl)(0.010 L)(0.005 M)(0.020 L) = (M HCl)(0.010 L)

M HCl = 0.01 M M HCl = 0.01 M

Problem 2Problem 2

In a titration, 27.4 mL of 0.0154 M In a titration, 27.4 mL of 0.0154 M Ba(OH)Ba(OH)22 is added to a 20.0 mL of is added to a 20.0 mL of

HCl of unknown concentration. HCl of unknown concentration. Determine the molarity of HCl.Determine the molarity of HCl.

2HCl2HCl + Ba(OH)+ Ba(OH)2 2 BaClBaCl22 + 2H + 2H22OO

2 mole 1 mole2 mole 1 mole

known: 27.4 mL of 0.0154M Ba(OH)known: 27.4 mL of 0.0154M Ba(OH)22

20 mL of HCl20 mL of HClunknown: M of HClunknown: M of HCl

(2)(0.0154 M)(0.0274 L) = (M HCl)(0.020 L)(2)(0.0154 M)(0.0274 L) = (M HCl)(0.020 L)

M HCl = 0.042 M M HCl = 0.042 M

Sample Problems 1 and 2

page 503

Section 19.5Section 19.5Salts in SolutionSalts in Solution


–Describe when a solution of a salt is acidic or basic.

Section 19.5Section 19.5Salts in SolutionSalts in Solution


–Demonstrate with equations how buffers resist changes in pH.

Salt HydrolysisSalt Hydrolysis A A saltsalt is an ionic compound that: is an ionic compound that:

–comes from the anion of an acid

–comes from the cation of a base

–is formed from a neutralization reaction

–some neutral; others acidic or basic ““Salt hydrolysisSalt hydrolysis”” - a - a saltsalt that reacts that reacts

with water to produce an acid or basewith water to produce an acid or base

Salt HydrolysisSalt Hydrolysis To see if the resulting salt is To see if the resulting salt is

acidic or basic, check the acidic or basic, check the “parent” acid and base“parent” acid and base that that formed it. Practice on these:formed it. Practice on these:

HCl + NaOH H2SO4 + NH4OH

CH3COOH + KOH

NaCl, a neutral salt

(NH4)2SO4, acidic salt

CH3COOK, basic salt

Salt HydrolysisSalt Hydrolysis Hydrolyzing salts usually come from:Hydrolyzing salts usually come from:

1. a strong acid + a weak base, or2. a weak acid + a strong base

Strong refers to the Strong refers to the degree of degree of ionizationionization

A strong Acid + a strong Base = Neutral Salt How do you How do you knowknow if it’s strong? if it’s strong?

– Refer to the handout provided (downloadable from my web site)

“acids, bases, and salts”. acids-bases n objectives: –define the properties of acids and bases

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