chapter 19acids, bases, and salts pre-ap chemistry bmhs anahit pivazyan

Chapter 19“Acids,

Bases, and Salts”

Pre-AP Chemistry

BMHS

Anahit Pivazyan

Section 19.1Section 19.1Acid-Base TheoriesAcid-Base Theories

OBJECTIVES:OBJECTIVES:

DefineDefine the the propertiesproperties of of acids and bases.acids and bases.

Properties of AcidsProperties of AcidsThey taste They taste soursour (don’t try this at home). (don’t try this at home).They can They can conduct electricityconduct electricity..

Can be strong or weak electrolytes in Can be strong or weak electrolytes in aqueous solutionaqueous 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 AcidsThey 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.It usually starts with Hydrogen.HHCl, Cl, HH22SOSO44, , HHNONO33,H,H33POPO44 etc. etc.

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

Sulfuric AcidSulfuric Acid = H = H22SOSO44 Highest volume Highest volume

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

Used in the production Used in the production of paperof paper

Used in production of Used in production of fertilizersfertilizers

Used in petroleum Used in petroleum refining; auto batteriesrefining; auto batteries

Nitric AcidNitric Acid = HNO = HNO33 Used in the production Used in the production

of fertilizersof fertilizers Used in the production Used in the production

of explosivesof explosives Nitric acid is a Nitric acid is a volatile volatile

acid – its reactive acid – its reactive components evaporate components evaporate easilyeasily

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

Hydrochloric AcidHydrochloric Acid = HCl = HCl Used in the “pickling” Used in the “pickling”

of steelof steel Used to purify Used to purify

magnesium from sea magnesium from sea waterwater

Part of gastric juice, it Part of gastric juice, it aids in the digestion of aids in the digestion of proteinsproteins

Sold commercially as Sold commercially as Muriatic acidMuriatic acid

Phosphoric AcidPhosphoric Acid = H = H33POPO44 A flavoring agent in A flavoring agent in

sodas (adds “tart”)sodas (adds “tart”) Used in the Used in the

manufacture of manufacture of detergentsdetergents

Used in the Used in the manufacture of manufacture of fertilizersfertilizers

NotNot a common a common laboratory reagentlaboratory reagent

Acetic AcidAcetic Acid = HC = HC22HH33OO2 2 (also called Ethanoic Acid, CH(also called Ethanoic Acid, CH33COOH)COOH)

Used in the manufacture Used in the manufacture of plasticsof plastics

Used in making Used in making pharmaceuticalspharmaceuticals

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

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 solutionChange 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 drain cleaner; soaplye for drain cleaner; soap))

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

Magnesium hydroxide, Magnesium hydroxide, Mg(OH)Mg(OH)22 ((Milk of MagnesiaMilk of Magnesia))

Calcium hydroxide, Calcium hydroxide, Ca(OH)Ca(OH)22 ((limelime; ; masonrymasonry))

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.

AcidsAcidsNot 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 ionsonly those that have only those that have very polar very polar

bondsbonds are ionizable - this is are ionizable - this is when the when the hydrogen is joined to hydrogen is joined to a very electronegative elementa very electronegative element

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)

Section 19.2Section 19.2Hydrogen Ions and AcidityHydrogen Ions and Acidity


DescribeDescribe how [H how [H1+1+] and ] and [OH[OH1-1-] are ] are relatedrelated in an in an aqueous solution.aqueous solution.



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



ConvertConvert hydrogen-ion hydrogen-ion concentrations concentrations into pH into pH valuesvalues and hydroxide-ion and hydroxide-ion concentrations into pOH concentrations into pOH values.values.



DescribeDescribe the the purposepurpose of of an acid-base indicator.an acid-base indicator.

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

HH22O O ↔↔ H H1+1+ + OH + OH1-1-

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

[H[H1+1+ ] = [OH ] = [OH1-1-] = 1 x 10] = 1 x 10-7 -7 MMSince 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 “ion product constantion product constant” for water” for water

Ion Product ConstantIon Product Constant HH22O O ↔↔ H H1+1+ + OH + OH1-1-

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”Basic solutions also called “alkaline”

- Page 596

The pH concept – from 0 to 14The pH concept – 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 (from 0 to 7 is the acid range) in in basebase, pH > 7 (7 to 14 is base 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 = 14Thus, a solution with a pOH Thus, a solution with a pOH

less than 7 is basic; with a pOH less than 7 is basic; with a pOH greater than 7 is an acidgreater than 7 is an acid

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

pH and Significant FigurespH and Significant Figures

For pH calculations, the hydrogen ion For pH calculations, the hydrogen ion concentration is usually expressed in concentration is usually expressed in scientific notationscientific 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 numbers to , with the two numbers to the right of the decimal corresponding the right of the decimal corresponding to the two significant figuresto the two significant figures

- Page 599

- Page 600

Measuring pHMeasuring pHWhy measure pH?Why measure pH?

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

Some of the Some of the many pH many pH

Indicators Indicators and theirand theirpH rangepH range

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

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

temperaturetemperature (25 (25 ooC), thus may C), thus may change at different temperatureschange at different temperatures

what if the solution what if the solution already has a already has a colorcolor, like paint?, like paint?

the the ability of the human eyeability of the human eye to to distinguish colors is limiteddistinguish colors is limited

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

resultsresultssome are some are largelarge, others portable, others portableworks by measuring the works by measuring the voltagevoltage

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

Instruments need to be Instruments need to be calibratedcalibratedFig. 19.15, p.603Fig. 19.15, p.603

StrengthStrengthAcids 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:StrongStrong are are completely ionizedcompletely ionized in in

aqueous solution; this means they aqueous solution; this means they ionize 100 %ionize 100 %

WeakWeak ionize only ionize only slightlyslightly in aqueous in aqueous solutionsolution

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, But, not much dissolves-not much dissolves- so it so it

is not concentratedis 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 equilibriumAcid 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. ConcentrationThe 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?

Acid-Base ReactionsAcid-Base Reactions

Acid + Base Acid + Base Water + Salt Water + SaltProperties related to every day:Properties related to every day:

antacids depend on neutralizationantacids depend on neutralizationfarmers adjust the soil pHfarmers adjust the soil pHformation of cave stalactitesformation of cave stalactiteshuman body kidney stones from human body kidney stones from

insoluble saltsinsoluble salts

Acid-Base ReactionsAcid-Base ReactionsNeutralization 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) NaCl NaCl(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)

TitrationTitrationThe 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 reactionAn An indicatorindicator is used to show is used to show

when neutralization has occurredwhen neutralization has occurredOften we use Often we use phenolphthaleinphenolphthalein- -

because it is colorless in neutral because it is colorless in neutral and acid; turns pink in baseand acid; turns pink in base

Steps - Neutralization reactionSteps - Neutralization reaction

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

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

#3. A base of known concentration is #3. A base of known concentration is slowly added, until the indicator slowly added, until the indicator changes color; measure the volumechanges color; measure the volumeFigure 19.22, page 615Figure 19.22, page 615

BuffersBuffersBuffersBuffers 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 addedmade from a made from a pair of chemicalspair of chemicals: :

a a weak acid and one of it’s weak acid and one of it’s saltssalts; or a ; or a weak base and one weak base and one of it’s saltsof it’s salts

BuffersBuffersA 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 waterSince it is a Since it is a pairpair of chemicals: of chemicals:

one chemical neutralizes any one chemical neutralizes any acidacid added, while the other chemical added, while the other chemical would neutralize any additional would neutralize any additional basebase

AND, they AND, they produce each otherproduce each other in the process!!!in the process!!!

BuffersBuffersThe two buffers that are crucial to The two buffers that are crucial to

maintain the pH of human blood are:maintain the pH of human blood are:

1. carbonic acid (H1. carbonic acid (H22COCO33) & hydrogen ) & hydrogen

carbonate (HCOcarbonate (HCO331-1-))

2. dihydrogen phosphate (H2. dihydrogen phosphate (H22POPO441-1-) & ) &

monohydrogen phoshate (HPOmonohydrogen phoshate (HPO442-2-) )

Table 19.10, page 621 has some Table 19.10, page 621 has some important buffer systemsimportant buffer systems

Conceptual Problem 19.2, p. 622Conceptual Problem 19.2, p. 622

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. What about the cost compared to plain aspirin?

chapter 19acids, bases, and salts pre-ap chemistry bmhs anahit pivazyan

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