“Acids, Bases, and Salts”

Honors Chemistry

Acid-Base TheoriesAcid-Base Theories

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?

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

ExamplesSour Milk –lactic acid

Vinegar- acetic acid

Soda – phosphoric acid

Lemons and oranges – citric acid

Grape 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.

ExamplesHousehold cleaners – ammonia

Drain and oven cleaners- NaOH

Antacids – magnesium hydroxide,

aluminum hydroxide and

sodium 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 to form water and a to form water and a

salt.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)

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

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 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

Acids Acids NeutralizeNeutralize Bases Bases

HCl + NaOH → NaCl + H2O

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

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

Properties of BasesProperties of Bases

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

aqueous solutionaqueous solution Change the colorChange the color of indicators (red of indicators (red

litmus turns blue).litmus turns blue).

Examples of BasesExamples of Bases

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

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

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

Magnesia)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).

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 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

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

waterwater (HCl (HCl → → HH1+1+ + Cl + Cl1-1-)) BasesBases produce hydroxide ions (OH produce hydroxide ions (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.

AcidsAcids 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

(O, F, Br)

Arrhenius examples...Arrhenius examples... Consider HCl = it is an acid!Consider HCl = it is an acid!

What about CHWhat about CH44 (methane)? (methane)?

CHCH33COOH (acetic acid) - it has COOH (acetic acid) - it has 4 hydrogens just like methane 4 hydrogens just like methane but one hydrogen is bound to but one hydrogen is bound to an oxygen atom.an oxygen atom.

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.

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 its its hydrogen ionhydrogen ion

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

Hydrogen Ions and AcidityHydrogen Ions and Acidity

OBJECTIVES:OBJECTIVES:

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

Hydrogen Ions and AcidityHydrogen Ions and Acidity

OBJECTIVES:OBJECTIVES:

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

Hydrogen Ions and AcidityHydrogen Ions and Acidity

OBJECTIVES:OBJECTIVES:–Convert hydrogen-ion [H+]

concentrations into pH values and hydroxide-ion concentrations into pOH values.

Hydrogen Ions and AcidityHydrogen Ions and Acidity

OBJECTIVES:OBJECTIVES:

–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 MM 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

pHpH

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.

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?

2) What is the pH of a solution if 2) What is the pH of a solution if the [Hthe [H33O+] is 2.5 x 10O+] is 2.5 x 10-2-2 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

2) What is the pH of a solution if 2) What is the pH of a solution if the [Hthe [H33O+] is 2.5 x 10O+] is 2.5 x 10-2-2 M? M?

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 we might need a other times we might need a pH meterpH meter

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.

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

–Define strong acids and weak acids.

StrengthStrength Acids and Bases are classified Acids and Bases are classified

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

aqueous solution; this means they ionize 100 %

– Weak ionize only slightly in aqueous solution

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).

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:

–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

Neutralization ReactionsNeutralization Reactions

OBJECTIVES:OBJECTIVES:

–Define the products of an acid-base reaction.

Neutralization ReactionsNeutralization Reactions

OBJECTIVES:OBJECTIVES:–Explain how acid-base titration is

used to calculate the concentration of an acid or a base.

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

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 of to the moles of hydroxide ions (= neutralized!)hydroxide ions (= neutralized!)

Titration – Equivalence PointTitration – Equivalence Point

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

solution can be determined by 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

– 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.

M x V = M x VM x V = M x VAcid baseAcid base

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

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 HCl

unknown: 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

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End of Chapter