1 The Chemistry of Acids and Bases AP Chemistry Chapter 16.

11The Chemistry The Chemistry of Acids and of Acids and BasesBases

The Chemistry The Chemistry of Acids and of Acids and BasesBases AP Chemistry Chapter 16AP Chemistry Chapter 16

22

Acid and BasesAcid and Bases

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16.1-16.216.1-16.2

55Acids

Have a sour taste. Vinegar is a solution of acetic acid. CitrusHave a sour taste. Vinegar is a solution of acetic acid. Citrusfruits contain citric acid.fruits contain citric acid.

React with certain metals to produce hydrogen gasReact with certain metals to produce hydrogen gas..

React with carbonates and bicarbonates to produce carbon React with carbonates and bicarbonates to produce carbon dioxide gasdioxide gas

Have a bitter taste.Have a bitter taste.

Feel slippery. Many soaps contain bases.Feel slippery. Many soaps contain bases.

Bases

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66

Some Properties of Acids

Produce H+ (as H3O+) ions in water (the hydronium ion is a

hydrogen ion attached to a water molecule)

Taste sour

Corrode metals

Electrolytes

React with bases to form a salt and water

pH is less than 7

Turns blue litmus paper to red “Blue to Red A-CID”

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Anion Ending Acid Name

-ide hydro-(stem)-ic acid

-ate (stem)-ic acid

-ite (stem)-ous acid

Acid Nomenclature Review

Binary Binary

Ternary Ternary

An easy way to remember which goes with which…An easy way to remember which goes with which…

““In the cafeteria, youIn the cafeteria, you ATEATE somethingsomething ICICky”ky”

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88Acid Nomenclature Flowchart

h yd ro - p re fix-ic en d in g

2 e lem en ts

-a te en d in gb ecom es-ic en d in g

-ite en d in gb ecom es

-o u s en d in g

n o h yd ro - p re fix

3 e lem en ts

AC ID Ss ta rt w ith 'H '

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99

• HBr HBr (aq)(aq)

• HH22COCO33

• HH22SOSO33

hydrohydrobromicbromic acidacid

carboncarbonicic acidacid

sulfursulfurousous acidacid

Acid Nomenclature Review

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1010

Name ‘Em!

• HI HI

• HCl HCl

• HH22SOSO33

• HNOHNO33

• HCIOHCIO44

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Some Properties of Bases

Produce OHProduce OH-- ions in water ions in water

Taste bitter, chalkyTaste bitter, chalky

Are electrolytesAre electrolytes

Feel soapy, slipperyFeel soapy, slippery

React with acids to form salts and waterReact with acids to form salts and water

pH greater than 7pH greater than 7

Turns red litmus paper to blue “Turns red litmus paper to blue “BBasic asic BBlue”lue”

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Some Common Bases

NaOHNaOH sodium hydroxidesodium hydroxide lyelye

KOHKOH potassium hydroxidepotassium hydroxide liquid soapliquid soap

Ba(OH)Ba(OH)22 barium hydroxidebarium hydroxide stabilizer for plasticsstabilizer for plastics

Mg(OH)Mg(OH)22 magnesium hydroxidemagnesium hydroxide “MOM” Milk of magnesia“MOM” Milk of magnesia

Al(OH)Al(OH)33 aluminum hydroxidealuminum hydroxide Maalox (antacid)Maalox (antacid)

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Acid/Base definitions

• Definition #1: Arrhenius (traditional)

Acids – produce H+ ions (or hydronium ions H3O+)

Bases – produce OH- ions

(problem: some bases don’t have hydroxide ions!)

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1414Arrhenius acid is a substance that produces H+ (H3O+) in water

Arrhenius base is a substance that produces OH- in water

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1515

Acid/Base Definitions

• Definition #2: Brønsted – Lowry

Acids – proton donor

Bases – proton acceptor

A “proton” is really just a hydrogen atom that has lost it’s electron!

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A Brønsted-Lowry acid is a proton donorA Brønsted-Lowry base is a proton acceptor

acidconjugate

basebase conjugate

acid

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ACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIESACID-BASE THEORIES

The Brønsted definition means NHThe Brønsted definition means NH33 is is aa BASEBASE in water — and water is in water — and water is itself anitself an ACIDACID

BaseAcidAcidBaseNH4

+ + OH-NH3 + H2OBaseAcidAcidBase

NH4+ + OH-NH3 + H2O

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Conjugate PairsConjugate Pairs16.1-16.216.1-16.2

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Learning Check!

Label the acid, base, conjugate acid, and Label the acid, base, conjugate acid, and conjugate base in each reaction:conjugate base in each reaction:

HCl + OHHCl + OH-- Cl Cl-- + H + H22OO HCl + OHHCl + OH-- Cl Cl-- + H + H22OO

HH22O + HO + H22SOSO44 HSO HSO44-- + H + H33OO

++ HH22O + HO + H22SOSO44 HSO HSO44-- + H + H33OO

++

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2020Acids & Base Acids & Base DefinitionsDefinitions

Lewis acid - a Lewis acid - a substance that substance that accepts an electron accepts an electron pairpair

Lewis base - a Lewis base - a substance that substance that donates an electron donates an electron pairpair

Definition #3 – Lewis Definition #3 – Lewis

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Formation ofFormation of hydronium ion hydronium ion is also an is also an excellent example.excellent example.

Lewis Acids & BasesLewis Acids & Bases

•Electron pair of the new O-H bond Electron pair of the new O-H bond originates on the Lewis base.originates on the Lewis base.

HH

H

BASE

••••••

O—HO—H

H+

ACID

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Lewis Acid/Base ReactionLewis Acid/Base Reaction16.1116.11

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Autoionzation of WaterAutoionzation of Water

HH22O can function as both an ACID and a BASE.O can function as both an ACID and a BASE.

In pure water there can beIn pure water there can be AUTOIONIZATIONAUTOIONIZATION

Equilibrium constant for water = KEquilibrium constant for water = Kww

KKww = [H = [H33OO++] [OH] [OH--] =] = 1.00 x 101.00 x 10-14-14 at 25 at 25 ooCC

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More About WaterMore About Water

In a In a neutral neutral solution [Hsolution [H33OO++] = [OH] = [OH--]]

OH-

H3O+

OH-

H3O+

AutoionizationAutoionization

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• Acidic solution

[H+ ] > [OH- ]

• Neutral solution

[H+ ] = [OH- ]

• Basic solution

[H+ ] < [OH- ]

StrengthStrength16.316.3

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Practice!

Autoionization of Water Practice Problem

Calculate the concentration of H+ ions (aq) in

• (a) a solution in which [OH-] is 0.010 M

• (b) a solution in which [OH-] is 2.0 x 10-9 M

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The The pH scalepH scale is a way of is a way of expressing the strength of expressing the strength of

acids and bases. acids and bases.

Instead of using very small Instead of using very small numbers, we just use the numbers, we just use the NEGATIVE power of 10 on NEGATIVE power of 10 on

the Molarity of the Hthe Molarity of the H++ (or OH (or OH--) ) ion.ion.

Under 7 = acidUnder 7 = acid7 = neutral7 = neutral

Over 7 = baseOver 7 = base

pH Scale

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pH of Common pH of Common SubstancesSubstances

2929

pH in Life

• The Hydrangea macrophylla blossoms in pink or blue, depending on soil pH.

• In acidic soils, the flowers are blue;

• in alkaline soils, the flowers are pink.

3030Calculating the pH

pH = - log [H+](Remember that the [ ] mean Molarity)

Example: If [H+] = 1 X 10-10

pH = - log 1 X 10-10

pH = - (- 10)

pH = 10

Example: If [H+] = 1.8 X 10-5

pH = - log 1.8 X 10-5

pH = - (- 4.74)

pH = 4.74

3131

Try These!Try These!

Find the pH of these:Find the pH of these:

For ExampleFor Example: A sample of freshly pressed apple : A sample of freshly pressed apple juice has a pH of 3.76. Calculate the [Hjuice has a pH of 3.76. Calculate the [H++].].

1)1) A 0.15 M solution of Hydrochloric acidA 0.15 M solution of Hydrochloric acid

2) A 3.00 X 102) A 3.00 X 10-7-7 M solution of Nitric acid M solution of Nitric acid

3232pH calculations – Solving for pH calculations – Solving for H+H+pH calculations – Solving for pH calculations – Solving for H+H+

If the pH of Coke is 3.12, [HIf the pH of Coke is 3.12, [H++] = ???] = ???

Because pH = - log [HBecause pH = - log [H++] then] then

- pH = log [H- pH = log [H++]]

Take antilog (10Take antilog (10xx) of both) of both sides and get sides and get

1010-pH -pH == [H[H++]][H[H++] = 10] = 10-3.12-3.12 = 7.6 x 10 = 7.6 x 10-4-4 M M *** to find antilog on your calculator, look for “Shift” or “2*** to find antilog on your calculator, look for “Shift” or “2nd nd

function” and then the log buttonfunction” and then the log button

3333pH calculations – Solving for pH calculations – Solving for H+H+

• A solution has a pH of 8.5. What is the A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the Molarity of hydrogen ions in the solution?solution?

pH = - log [HpH = - log [H++]]

8.5 = - log [H8.5 = - log [H++]]

-8.5 = log [H-8.5 = log [H++]]

Antilog -8.5 = antilog (log [HAntilog -8.5 = antilog (log [H++])])

1010-8.5-8.5 = [H = [H++]]

3.16 X 103.16 X 10-9-9 = [H = [H++]]

pH = - log [HpH = - log [H++]]

8.5 = - log [H8.5 = - log [H++]]

-8.5 = log [H-8.5 = log [H++]]

Antilog -8.5 = antilog (log [HAntilog -8.5 = antilog (log [H++])])

1010-8.5-8.5 = [H = [H++]]

3.16 X 103.16 X 10-9-9 = [H = [H++]]

3434pOH

• Since acids and bases are Since acids and bases are opposites, pH and pOH are opposites, pH and pOH are opposites!opposites!

• pOH does not really exist, but it is pOH does not really exist, but it is useful for changing bases to pH.useful for changing bases to pH.

• pOH looks at the perspective of a pOH looks at the perspective of a basebase

pOH = - log [OHpOH = - log [OH--]]Since pH and pOH are on opposite Since pH and pOH are on opposite

ends,ends,pH + pOH = 14pH + pOH = 14

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pHpH [H+][H+] [OH-][OH-] pOHpOH

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[H[H33OO++], [OH], [OH--] and pH] and pHWhat is the pH of the What is the pH of the

0.0010 M NaOH solution? 0.0010 M NaOH solution?

[OH-] = 0.0010 (or 1.0 X 10[OH-] = 0.0010 (or 1.0 X 10-3-3 M) M)

pOH = - log 0.0010pOH = - log 0.0010

pOH = 3pOH = 3

pH = 14 – 3 = 11pH = 14 – 3 = 11

OR KOR Kww = [H = [H33OO++] [OH] [OH--]]

[H[H3OO++] = 1.0 x 10] = 1.0 x 10-11-11 M M

pH = - log (1.0 x 10pH = - log (1.0 x 10-11-11) = 11.00) = 11.00

3737The pH of rainwater collected in a certain region of the northeastern United States on a particular day was 4.82. What is the H+ ion concentration of the rainwater?

The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood?

3838Calculating [H3O+], pH, [OH-], and pOH

Problem 1: A chemist dilutes concentrated hydrochloric acid to make two solutions: (a) 3.0 M and (b) 0.0024 M. Calculate the [H3O+], pH, [OH-], and pOH of the two solutions at 25°C.

Problem 2: What is the [H3O+], [OH-], and pOH of a solution with pH = 3.67? Is this an acid, base, or neutral?

Problem 3: Problem #2 with pH = 8.05?

3939

HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.

Strong and Weak Strong and Weak Acids/BasesAcids/Bases

The strength of an acid (or base) is determined by the amount of IONIZATION.

The strength of an acid (or base) is determined by the amount of IONIZATION.

4040


• Generally divide acids and bases into STRONG or Generally divide acids and bases into STRONG or WEAK ones.WEAK ones.

STRONG ACID:STRONG ACID: HNOHNO3 3 (aq) + H(aq) + H22O (l) --->O (l) --->

HH33OO+ + (aq) + NO(aq) + NO33- - (aq)(aq)

HNOHNO33 is about 100% dissociated in water. is about 100% dissociated in water.

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• Weak acidsWeak acids are much less than 100% ionized in are much less than 100% ionized in

water.water.

One of the best known is acetic acid = CHOne of the best known is acetic acid = CH33COCO22HH



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• Strong Base:Strong Base: 100% dissociated in 100% dissociated in water.water.

NaOH (aq) ---> NaNaOH (aq) ---> Na+ + (aq) + OH(aq) + OH- - (aq)(aq)


Other common strong Other common strong bases include KOH andbases include KOH and Ca(OH)Ca(OH)22..

CaO (lime) + HCaO (lime) + H22O -->O -->

Ca(OH)Ca(OH)22 (slaked lime) (slaked lime)CaOCaO

4343

• Weak base:Weak base: less than 100% ionized less than 100% ionized in waterin water

One of the best known weak bases is One of the best known weak bases is ammoniaammonia

NHNH3 3 (aq) + H(aq) + H22O (l) O (l) NH NH44+ + (aq) + OH(aq) + OH- - (aq)(aq)



4444

Weak BasesWeak Bases

4545

Equilibria Involving Equilibria Involving Weak Acids and BasesWeak Acids and Bases

Consider acetic acid, HCConsider acetic acid, HC22HH33OO22 (HOAc) (HOAc)

HCHC22HH33OO22 + H + H22O O H H33OO++ + C + C22HH33OO22 --

AcidAcid Conj. base Conj. base

Ka [H3O+][OAc- ]

[HOAc] 1.8 x 10-5Ka

[H3O+][OAc- ][HOAc]

1.8 x 10-5

(K is designated K(K is designated Kaa for ACID) for ACID)

K gives the ratio of ions (split up) to molecules K gives the ratio of ions (split up) to molecules

(don’t split up)(don’t split up)

4646Ionization Constants for Ionization Constants for Acids/Bases Acids/Bases

AcidsAcids ConjugateConjugateBasesBases

Increase strength

Increase strength

4747

Equilibrium Constants Equilibrium Constants for Weak Acidsfor Weak Acids

Equilibrium Constants Equilibrium Constants for Weak Acidsfor Weak Acids

Weak acid has KWeak acid has Kaa < 1 < 1

Leads to small [HLeads to small [H33OO++] and a pH of 2 - 7] and a pH of 2 - 7

4848

Equilibrium Constants Equilibrium Constants for Weak Basesfor Weak Bases

Equilibrium Constants Equilibrium Constants for Weak Basesfor Weak Bases

Weak base has KWeak base has Kbb < 1 < 1

Leads to small [OHLeads to small [OH--] and a pH of 12 - 7] and a pH of 12 - 7

4949

Relation Relation

of Kof Kaa, K, Kbb, ,

[H[H33OO++] ]

and pHand pH

5050Equilibria Involving A Weak Equilibria Involving A Weak AcidAcid

Equilibria Involving A Weak Equilibria Involving A Weak AcidAcid

You have 1.00 M HOAc. Calc. the You have 1.00 M HOAc. Calc. the equilibrium concs. of HOAc, Hequilibrium concs. of HOAc, H33OO++, OAc, OAc--, ,

and the pH.and the pH.

Step 1.Step 1. Define equilibrium concs. in ICE Define equilibrium concs. in ICE

table.table.

[HOAc][HOAc] [H[H33OO++]] [OAc[OAc--]]

initialinitial

changechange

equilibequilib

1.001.00 00 001.001.00 00 00

-x-x +x+x +x+x-x-x +x+x +x+x

1.00-x1.00-x xx xx1.00-x1.00-x xx xx



Step 2.Step 2. Write KWrite Kaa expression expression

You have 1.00 M HOAc. Calc. the equilibrium concs. You have 1.00 M HOAc. Calc. the equilibrium concs. of HOAc, Hof HOAc, H33OO++, OAc, OAc--, and the pH., and the pH.

Ka 1.8 x 10-5 = [H3O+][OAc- ]

[HOAc]

x2

1.00 - xKa 1.8 x 10-5 =

[H3O+][OAc- ][HOAc]

x2

1.00 - x

This is a quadratic. Solve using quadratic This is a quadratic. Solve using quadratic formula.formula.

or you can make an approximation if x is very or you can make an approximation if x is very small! (Rule of thumb: 10small! (Rule of thumb: 10-5-5 or smaller is ok) or smaller is ok)or you can make an approximation if x is very or you can make an approximation if x is very small! (Rule of thumb: 10small! (Rule of thumb: 10-5-5 or smaller is ok) or smaller is ok)



Step 3.Step 3. Solve KSolve Kaa expression expression


Ka 1.8 x 10-5 = [H3O+][OAc- ]

[HOAc]

x2

1.00 - xKa 1.8 x 10-5 =

[H3O+][OAc- ][HOAc]

x2

1.00 - x

First assume x is very small because First assume x is very small because KKaa is so small. is so small.

Ka 1.8 x 10-5 = x2

1.00Ka 1.8 x 10-5 =

x2

1.00

Now we can more easily solve this Now we can more easily solve this approximate expression.approximate expression.

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Equilibria Involving A Weak AcidEquilibria Involving A Weak AcidEquilibria Involving A Weak AcidEquilibria Involving A Weak Acid

Step 3.Step 3. Solve KSolve Kaa approximateapproximate expressionexpression


Ka 1.8 x 10-5 = x2

1.00Ka 1.8 x 10-5 =

x2

1.00

x =x = [[HH33OO++] = [] = [OAcOAc--] = 4.2 x 10] = 4.2 x 10-3-3 M M

pH = - log [pH = - log [HH33OO++] = -log (4.2 x 10] = -log (4.2 x 10-3-3) =) = 2.372.37



Calculate the pH of a 0.0010 M solution of Calculate the pH of a 0.0010 M solution of formic acid, HCOformic acid, HCO22H.H.

HCOHCO22H + HH + H22O O HCO HCO22-- + H + H33OO++

KKaa = 1.8 x 10 = 1.8 x 10-4-4

Approximate solutionApproximate solution

[H[H33OO++] = 4.2 x 10] = 4.2 x 10-4-4 M, M, pH = 3.37pH = 3.37

Exact SolutionExact Solution

[H[H33OO++] = [HCO] = [HCO22--] = 3.4 x 10] = 3.4 x 10-4-4 M M

[HCO[HCO22H] = 0.0010 - 3.4 x 10H] = 0.0010 - 3.4 x 10-4-4 = 0.0007 M = 0.0007 M

pH = 3.47 pH = 3.47

5555Equilibria Involving A Weak Equilibria Involving A Weak BaseBase

You have 0.010 M NHYou have 0.010 M NH33. Calc. the pH.. Calc. the pH.

NHNH33 + H + H22O O NH NH44++ + OH + OH--

KKbb = 1.8 x 10 = 1.8 x 10-5-5

Step 1.Step 1. Define equilibrium concs. in ICE tableDefine equilibrium concs. in ICE table

[NH[NH33]] [NH[NH44++]] [OH[OH--]]

initialinitial

changechange

equilibequilib

0.0100.010 00 000.0100.010 00 00


0.010 - x0.010 - x x x xx0.010 - x0.010 - x x x xx




KKbb = 1.8 x 10 = 1.8 x 10-5-5

Step 1.Step 1. Define equilibrium concs. in ICE tableDefine equilibrium concs. in ICE table

[NH[NH33]] [NH[NH44++]] [OH[OH--]]

initialinitial

changechange

equilibequilib

0.0100.010 00 000.0100.010 00 00


0.010 - x0.010 - x x x xx0.010 - x0.010 - x x x xx




KKbb = 1.8 x 10 = 1.8 x 10-5-5

Step 2.Step 2. Solve the equilibrium expressionSolve the equilibrium expression

Kb 1.8 x 10-5 = [NH4

+][OH- ][NH3 ]

= x2

0.010 - xKb 1.8 x 10-5 =

[NH4+][OH- ]

[NH3 ] =

x2

0.010 - x

Assume x is small, soAssume x is small, so x = [OHx = [OH--] = [NH] = [NH44

++] = 4.2 x 10] = 4.2 x 10-4-4 M M

and [NHand [NH33] = 0.010 - 4.2 x 10] = 0.010 - 4.2 x 10-4-4 ≈ 0.010 M ≈ 0.010 M

The approximation is validThe approximation is valid !!




KKbb = 1.8 x 10 = 1.8 x 10-5-5

Step 3.Step 3. Calculate pHCalculate pH

[OH[OH--] = 4.2 x 10] = 4.2 x 10-4-4 M M

so pOH = - log [OHso pOH = - log [OH--] = 3.37] = 3.37

Because pH + pOH = 14,Because pH + pOH = 14,

pH = 10.63pH = 10.63

5959

Types of Acid/Base Reactions: Types of Acid/Base Reactions: SummarySummary

6060pH testing

• There are several ways to test pHThere are several ways to test pH

–Blue litmus paper (red = acid)Blue litmus paper (red = acid)

–Red litmus paper (blue = basic)Red litmus paper (blue = basic)

–pH paper (multi-colored)pH paper (multi-colored)

–pH meter (7 is neutral, <7 acid, >7 pH meter (7 is neutral, <7 acid, >7 base)base)

–Universal indicator (multi-colored)Universal indicator (multi-colored)

– Indicators like phenolphthaleinIndicators like phenolphthalein

–Natural indicators like red cabbage, Natural indicators like red cabbage, radishesradishes

6161Paper testing

• Paper tests like litmus paper and pH Paper tests like litmus paper and pH paperpaper

– Put a stirring rod into the solution Put a stirring rod into the solution and stir.and stir.

– Take the stirring rod out, and Take the stirring rod out, and place a drop of the solution from place a drop of the solution from the end of the stirring rod onto a the end of the stirring rod onto a piece of the paperpiece of the paper

– Read and record the color change. Read and record the color change. Note what the color indicates. Note what the color indicates.

– You should only use a small You should only use a small portion of the paper. You can use portion of the paper. You can use one piece of paper for several one piece of paper for several tests.tests.

6262pH paperpH paper

6363

pH meter

• Tests the voltage of the Tests the voltage of the electrolyteelectrolyte

• Converts the voltage to Converts the voltage to pHpH

• Very cheap, accurateVery cheap, accurate

• Must be calibrated with Must be calibrated with a buffer solutiona buffer solution

6464pH indicators

• Indicators are dyes that can be added that will change color in the presence of an acid or base.

• Some indicators only work in a specific range of pH

• Once the drops are added, the sample is ruined

• Some dyes are natural, like radish skin or red cabbage

1 The Chemistry of Acids and Bases AP Chemistry Chapter 16.

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Transcript of 1 The Chemistry of Acids and Bases AP Chemistry Chapter 16.