Chapter 19 “ Acids, Bases, and Salts ”

Chapter 19“Acids, Bases,

and Salts”

Properties of AcidsProperties of Acids They 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 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!)

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 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 kill bacteria in Used to kill bacteria in

poolspools 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 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 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 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 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

Acids Acids have have a pH a pH less less 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 Arrhenius (1859-1927)Svante Arrhenius (1859-1927)

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.

Hubert N. Alyea (1903-1996)Hubert N. Alyea (1903-1996)

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.

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…?

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..

Chemical IndicatorsChemical Indicators?? They are weak They are weak acids or bases that have a different acids or bases that have a different color from their original acid and basecolor from their original acid and base

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)

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 “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 “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”

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)

– in base, 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 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

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

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.

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–Fig. 19.15, p.603

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

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

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 adjust the 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)

– Table 19.9, page 613 lists some salts

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 is a 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!)

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 19.22, page 615

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 19.7, page 616