chapter 16 “acids, bases, and salts”

Chapter 16 Chapter 16 “Acids, Bases, “Acids, Bases,

and Salts”and Salts”

OBJECTIVES:OBJECTIVES:

–Define the properties of acids and bases.

Acid-Base TheoriesAcid-Base Theories

–Compare and contrast acids and bases as defined by the theories of Arrhenius, Bronsted-Lowry, and Lewis.

Properties of acidsProperties of acids Taste sour (don’t try this at home).Taste sour (don’t try this at home). Conduct electricity.Conduct electricity.

–Can be strong or weak electrolytes in aqueous solution

React with metals to form HReact with metals to form H22 gas. gas. Change the color of indicators (blue Change the color of indicators (blue

litmus to red).litmus to red). React with bases (hydroxides) to form React with bases (hydroxides) to form

water and a salt.water and a salt.

Acids Affect IndicatorsAcids Affect Indicators

Blue litmus paper turns red in contact with an acid.

Acids have a pH less than 7Acids have a pH less than 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)

Acids React with CarbonatesAcids React with Carbonates

2HC2H3O2 + Na2CO3

2NaC2H3O2 + H2O + CO2

Effects of Acid Rain on MarbleEffects of Acid Rain on Marble(calcium (calcium carbonatecarbonate))

George Washington:BEFORE

George Washington:AFTER

Acids Neutralize BasesAcids Neutralize BasesHCl + NaOH → NaCl + H2O

-Neutralization reactions ALWAYS produce a salt 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 any production of any chemical in the U.S.chemical in the U.S.

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 refiningrefining

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 volatile Nitric acid is a volatile

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

Stains proteins Stains proteins (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 acid“Muriatic acid””

Phosphoric AcidPhosphoric Acid – H – H33POPO44o A flavoring agent in A flavoring agent in

sodassodaso Used in the Used in the

manufacture of manufacture of detergentsdetergents

o Used in the Used in the manufacture of manufacture of fertilizersfertilizers

o NotNot a common a common laboratory reagentlaboratory reagent

Acetic AcidAcetic Acid – HC – HC22HH33OO22

Used in the Used in the manufacture of plasticsmanufacture of plastics

Used in making Used in making pharmaceuticalspharmaceuticals

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

Properties of basesProperties of bases React with acids to form water React with acids to form water

and a salt.and a salt. Taste bitter.Taste bitter. Feel slippery (don’t try this either).Feel slippery (don’t try this either). Can be strong or weak Can be strong or weak

electrolytes in aqueous solutionelectrolytes in aqueous solution Change the color of indicators Change the color of indicators

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

Examples of BasesExamples of Bases Sodium hydroxide (lye), Sodium hydroxide (lye),

NaOHNaOH Potassium hydroxide, Potassium hydroxide,

KOHKOH Magnesium hydroxide, Magnesium hydroxide,

Mg(OH)Mg(OH)22

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

Bases Affect IndicatorsBases Affect Indicators

Red litmus paper turns blue in contact with a base.

Phenolphthalein turns purple in a base.

Bases Bases have a have a

pH pH greater greater 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

Svante ArrheniusSvante Arrhenius Swedish chemist (1859-1927) - Swedish chemist (1859-1927) -

Nobel prize winner in chemistry Nobel prize winner in chemistry (1903)(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

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

in aqueous solution.in aqueous solution. BasesBases produce hydroxide ions produce hydroxide ions

(OH(OH1-1-) when dissolved in water.) when dissolved in water. Limited to aqueous solutions.Limited to aqueous 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.Arrhenius base.

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

Polyprotic AcidsPolyprotic Acids Some compounds have more than Some compounds have more than

1 ionizable hydrogen.1 ionizable hydrogen. HNOHNO3 3 nitric acid - monoproticnitric acid - monoprotic

HH22SOSO44 sulfuric acid - diprotic - 2 H sulfuric acid - diprotic - 2 H++

HH33POPO44 phosphoric acid - triprotic - 3 phosphoric acid - triprotic - 3

Having more than one ionizable Having more than one ionizable hydrogen does not mean stronger!hydrogen does not mean stronger!

Polyprotic AcidsPolyprotic Acids However, not all compounds that However, not all compounds that

have hydrogen are acidshave hydrogen are acids 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

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

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

2. Brønsted-Lowry - 19232. Brønsted-Lowry - 1923 Broader definition than ArrheniusBroader 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.

HCl(g) + HHCl(g) + H22O(l) O(l) HH33OO++ + Cl + Cl--

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

Johannes Bronsted Thomas LowryJohannes Bronsted Thomas Lowry (1879-1947) (1874-1936) (1879-1947) (1874-1936)

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

base by using Bronsted-Lowry:base by using Bronsted-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 base”conjugate base” is the is the

remainder of the original acid, after remainder of the original acid, after it donates it’s hydrogen ionit donates it’s hydrogen ion

A “A “conjugate acid”conjugate acid” is the particle is the particle formed when the original base formed when the original base gains a hydrogen iongains a 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 acid + Conjugate baseConjugate base

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

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

acid base c.a. c.b.acid base c.a. c.b. Amphoteric – a substance that can act as Amphoteric – a substance that can act as

both and acid and base- as water showsboth and acid and base- as water shows

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.

Hydrogen Ions and AcidityHydrogen Ions and Acidity

–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:

H2O ↔ H1+ + OH1-

Called the “self ionization” of waterCalled the “self ionization” of water Occurs to a very small extent:Occurs to a very small 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 “ion product constant” for water is called the “ion product constant” for water

Ion Product ConstantIon Product Constant HH22O O ↔↔ H H++ + OH + OH--

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 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”

Ex. 16.3

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: pH = -log[Hdefinition: pH = -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 < 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 the base , pH > 7 (7 to 14 is the base

range)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 Thus, a solution with a pOH Thus, a solution with a pOH

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

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

ion concentration is expressed in ion concentration is 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 0.0010 has 2 significant figures 0.0010 has 2 significant figures

the pH = 3.00, with the two the pH = 3.00, with the two numbers to the right of the decimal numbers to the right of the decimal representing the two significant representing the two significant figuresfigures

- Page 599

Measuring pHMeasuring pH Why measure pH?Why measure pH?

– 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 indicators, other times indicators, other times we might need a pH we might need a pH metermeter

Measuring pH with wide-range paperMeasuring pH with wide-range paper

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

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

Some of the Some of the many pH many pH

Indicators Indicators and theirand theirrangesranges

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

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

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

–what if the solution already has 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

–needs to be calibrated–Fig. 19.15, p.603

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

–Define strong acids and weak acids.

Strengths of Acids and BasesStrengths of Acids and Bases

–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 Acids and Bases are classified

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

aqueous solution; this means they ionize 100 %

–Weak ionize only slightly in aqueous solution

StrengthStrength is different from is different from concentrationconcentration

StrengthStrength Strong – means it forms many Strong – means it forms many

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 when completely apart when dissolved. dissolved. –But, not much dissolves- so it

is not concentrated

Strong Acid DissociationStrong Acid Dissociation

Weak Acid DissociationWeak Acid Dissociation

Measuring strengthMeasuring strength Ionization is reversible.Ionization is reversible. HA HA ↔↔ H H++ + A + A- -

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

KKaa = [H = [H++ ][A ][A- - ] (water is constant)] (water is constant)

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

thus a larger Kthus a larger Kaa

What about bases?What about bases? Strong bases dissociate completely.Strong bases dissociate completely. MOH MOH ↔↔ 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 base = more dissociated Stronger base = more dissociated

ions are produced, thus a larger Kions are produced, thus a larger Kb.b.

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 refer to the extent of ionization of an acid or the extent of ionization of an acid or basebase

Is a concentrated weak acid possible?Is a concentrated weak acid possible?

16.7 Neutralization Reactions16.7 Neutralization Reactions

–Define the products of an acid-base reaction.

Neutralization ReactionsNeutralization Reactions

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

Neutralization ReactionsNeutralization Reactions OBJECTIVES:OBJECTIVES:

–Explain the concept of equivalence in neutralization reactions.

Neutralization ReactionsNeutralization Reactions

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

Acid-Base ReactionsAcid-Base Reactions

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

– antacids depend on neutralization– farmers use it to control soil pH– formation of cave stalactites– 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) 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)

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

a known amount of solution of a known amount of solution of known concentration to known concentration to determine the concentration of determine the concentration of another solutionanother solution

Remember? - a Remember? - a balanced balanced equationequation is a is a mole ratiomole ratio

- 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 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 volume– Figure 16.8, page 526

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

– Sample Problem 16.11, page 526

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; or a weak base 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

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

BuffersBuffers Example: Ethanoic (acetic) acid Example: Ethanoic (acetic) acid

and sodium ethanoate (also and sodium ethanoate (also called sodium acetate)called sodium acetate)

Examples on page 621 of theseExamples on page 621 of these The The buffer capacitybuffer capacity is the is the

amount of acid or base that can amount of acid or base that can be added before a significant be added before a significant change in pHchange in pH

BuffersBuffers The buffers that are crucial to The buffers that are crucial to

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

1. carbonic acid (H2CO3) & hydrogen

carbonate (HCO31-)

2. dihydrogen phosphate (H2PO41-) &

monohydrogen phoshate (HPO42-)

chapter 16 “acids, bases, and salts”

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