Acids and BasesAcids and Bases

Chapter 19Chapter 19

Ions in SolutionIons in Solution

Aqueous solutions contain HAqueous solutions contain H+ + ions and ions and OHOH- - ionsions

If a solution has more HIf a solution has more H+ + ions than OHions than OH- -

ions it is acidicions it is acidic If a solution has more OHIf a solution has more OH- - ions than Hions than H+ +

ions it is basicions it is basic If a solution has the same number of OHIf a solution has the same number of OH- -

ions and Hions and H+ + ions it is neutralions it is neutral

Properties of AcidsProperties of Acids

Properties acidsProperties acids – – Produce HProduce H++ ions when dissolved in water ions when dissolved in water taste sour taste sour Turn Blue Litmus paper PinkTurn Blue Litmus paper Pink React with metals to produce Hydrogen GasReact with metals to produce Hydrogen Gas

good at dissolving things (food in stomach, teeth good at dissolving things (food in stomach, teeth to form cavities, mineral deposits in coffeemaker)to form cavities, mineral deposits in coffeemaker)

Have a pH of 0 to < 7Have a pH of 0 to < 7 Conduct electricityConduct electricity

Properties of BasesProperties of Bases

Properties basesProperties bases – – taste bittertaste bitter feel slipperyfeel slippery tend to produce OHtend to produce OH-- ions when placed in ions when placed in

waterwater turn Red Litmus Paper Blueturn Red Litmus Paper Blue Have a pH of 7 to 14Have a pH of 7 to 14 Conduct electricityConduct electricity

Two models of Acids and Two models of Acids and BasesBases

ArrheniusArrhenius Bronsted-LowryBronsted-Lowry Two similar but different explanations, Two similar but different explanations,

both are correctboth are correct

ArrheniusArrhenius

Acid Acid - produces H - produces H++ in aqueous solution in aqueous solution HCl (g) HCl (g) H H+ + (aq) + Cl(aq) + Cl- - (aq)(aq)

BaseBase – produces OH – produces OH-- in aqueous solution in aqueous solution NaOH (s) NaOH (s) Na Na+ + (aq) + OH(aq) + OH- - (aq)(aq)

Explains most Acids and Bases, but not Explains most Acids and Bases, but not allall

Acid-Base Neutralization Acid-Base Neutralization ReactionReaction

When an acid and a base are mixed When an acid and a base are mixed together:together:

acid + base acid + base A salt and water are formed:A salt and water are formed:

a salt + watera salt + water remember remember a salta salt is any ionic compound is any ionic compound

ExamplesExamples

HCl (aq) + NaOH (aq) HCl (aq) + NaOH (aq) NaCl (aq) + H NaCl (aq) + H22O (l)O (l)

AcidAcid + Base+ Base A Salt + WaterA Salt + Water 2HCl(aq) + Ca(OH)2HCl(aq) + Ca(OH)22(aq) (aq) CaCl CaCl22(aq) + 2 H(aq) + 2 H22O(l)O(l)

AcidAcid + Base+ Base A Salt + WaterA Salt + Water

Bronsted-Lowry ModelBronsted-Lowry Model

Ammonia (NHAmmonia (NH33) is a base.) is a base.

It does not contain OHIt does not contain OH-- in it. in it. So according in Arrhenius it isn’t a base.So according in Arrhenius it isn’t a base. But when placed in water it produces OH, But when placed in water it produces OH,

so it must be a base.so it must be a base.

Bronsted-Lowry ModelBronsted-Lowry Model

The Bronsted-Lowry model focuses on The Bronsted-Lowry model focuses on HH++ ion ion

AcidAcid – H – H++ donor donor When placed in water Acids give HWhen placed in water Acids give H+ + awayaway HCl (g) + HHCl (g) + H22O (l) O (l) Cl Cl-- (aq) + H (aq) + H33OO++ (aq) (aq)

HH33OO++ (aq) is called the (aq) is called the Hydronium ionHydronium ion

BaseBase – H – H++ acceptor acceptor NHNH3 3 (aq) + H(aq) + H22O (l) O (l) NH NH44

++ (aq) + OH(aq) + OH--

Acid-Base PairsAcid-Base Pairs

In Bronsted-Lowry Acids and Bases you In Bronsted-Lowry Acids and Bases you must always have a pairmust always have a pair Every Acid must have a Conjugate BaseEvery Acid must have a Conjugate Base Every Base must have an Conjugate AcidEvery Base must have an Conjugate Acid

HCl (g) + HHCl (g) + H22O (l) O (l) Cl Cl-- (aq) + H (aq) + H33OO++ (aq) (aq)

Acid Base Con Base Con AcidAcid Base Con Base Con Acid HCl is an Acid and produces ClHCl is an Acid and produces Cl-- HH22O must be a Base and produces HO must be a Base and produces H33OO++

More on PairsMore on Pairs

HI(s) + HHI(s) + H22O(l) O(l) H H33OO++(aq) + I(aq) + I--(aq)(aq)

AcidAcid Base Base C.A. C.B. C.A. C.B. HH22SOSO44(s) + H(s) + H22O(l) O(l) H H33OO++(aq) + HSO(aq) + HSO44

--

(aq)(aq) AcidAcid Base Base C.A. C.B. C.A. C.B.

Strong AcidsStrong Acids

Strong acid Strong acid - reacts completely with water to - reacts completely with water to produce ions; no molecules are leftproduce ions; no molecules are left

Example: HCl + HExample: HCl + H22O O HH33OO++ + Cl + Cl-- The Six Strong Acids: The Six Strong Acids: 1.1. HCl (hydrochloric acid)HCl (hydrochloric acid)2.2. HBr (hydrobromic acid)HBr (hydrobromic acid)3.3. HI (hydroiodic acid)HI (hydroiodic acid)4.4. HH22SOSO44 (sulfuric acid) (sulfuric acid)5.5. HNOHNO33 (nitric acid) (nitric acid)6.6. HClOHClO44 (perchloric acid) (perchloric acid)

Strong acids:Strong acids:

HCl + HHCl + H22O O H H33OO++ + Cl- + Cl-

Remember, strong acids ionize completely in water. The reaction goes all the way to the right. A single arrow is used. There are virtually no HCl molecules left intact.

Strong acids:Strong acids:

HCl + HHCl + H22O O H H33OO++ + Cl- + Cl-

Looking at the equation above, with the single arrow, is Cl- a strong base or a weak base?

Weak AcidsWeak Acids

weak acidweak acid – reacts only slightly with – reacts only slightly with water to produce ions; mostly molecules water to produce ions; mostly molecules leftleft

HF + HHF + H22O O H H33OO++ + F+ F--

HH22COCO33 + H + H22O O H H33OO++ + HCO+ HCO33--

Notice: Only one H comes off at a timeNotice: Only one H comes off at a time

Strong BasesStrong Bases

Strong Base Strong Base - reacts completely with - reacts completely with water to produce ions; no molecules are water to produce ions; no molecules are leftleft

Strong Bases: Strong Bases: Group 1 metals and Sr, Ba, and Ra with OH Group 1 metals and Sr, Ba, and Ra with OH

presentpresent Examples NaOH, KOH, CsOH, Ba(OH)Examples NaOH, KOH, CsOH, Ba(OH)22

Weak BasesWeak Bases

weak Basesweak Bases – reacts only slightly with – reacts only slightly with water to produce ions; mostly molecules water to produce ions; mostly molecules leftleft

Examples:Examples: NHNH33 + H + H22O O NH NH44

++ + OH + OH--

Fe(OH)Fe(OH)33 + H + H22O O Fe Fe 3+ 3+ + 3 OH+ 3 OH--

General ruleGeneral rule: The : The conjugate base of a conjugate base of a strong acid is a weak strong acid is a weak base.base.Similarly, the conjugate Similarly, the conjugate acid of a strong base is a acid of a strong base is a weak acid.weak acid.

One more reminder:One more reminder:

“Weak” does not mean the same “Weak” does not mean the same thing as “diluted.”thing as “diluted.”

HCl, for example is always a strong HCl, for example is always a strong acid. If you add 1000 liters of water acid. If you add 1000 liters of water to it, it will be diluted, but still to it, it will be diluted, but still strong because what little there is strong because what little there is will be will be completely dissociated.completely dissociated.

Concentrated Vs DiluteConcentrated Vs Dilute

Concentrated means that there is a lot of Concentrated means that there is a lot of Acid/Base molecules for the amount of Acid/Base molecules for the amount of water or that the Molarity is Highwater or that the Molarity is High Concentrated HCl is 16 MConcentrated HCl is 16 M

Dilute means that there are not many Dilute means that there are not many Acid/Base molecules or that the Molarity Acid/Base molecules or that the Molarity is Lowis Low Diluted HCl would be 0.1 MDiluted HCl would be 0.1 M

Naming AcidsNaming Acids

Look at the names of these acids – can Look at the names of these acids – can you come up with the rule?you come up with the rule?

HH22SOSO44: sulfur: sulfuricic acid acid

HNOHNO33: nitr: nitricic acid acid

HH33POPO44: phosphor: phosphoricic acid acid

Naming acidsNaming acids

Rule #1: If the acid comes from a Rule #1: If the acid comes from a polyatomic ion that ends in “ate,” the acid polyatomic ion that ends in “ate,” the acid is named ____-ic.is named ____-ic.

HH22SOSO44: sulfur: sulfuricic acid (from sulfate) acid (from sulfate)

HNOHNO33: nitr: nitricic acid (from nitrate) acid (from nitrate)

HH33POPO44: phosphor: phosphoricic acid (from phosphate) acid (from phosphate)

Naming AcidsNaming Acids

Rule #2: If the acid does not have oxygen Rule #2: If the acid does not have oxygen in it, then name it…in it, then name it…

hydro + second element + ichydro + second element + ic

Example:Example:

HCl is hydrochloric acid.HCl is hydrochloric acid.

What would HBr be? HWhat would HBr be? H22S?S?

Water as an Acid and a Water as an Acid and a BaseBase

amphotericamphoteric – describes substance that – describes substance that can act as an acid or as a basecan act as an acid or as a base

Example: HExample: H22O (see previous Bronsted O (see previous Bronsted Lowry examples)Lowry examples)

Arrhenius: Arrhenius: HH22O O H H++ + OH + OH--

Bronsted Lowry: Bronsted Lowry: HH22O + HO + H22O O H H33OO++ + OH + OH--

Strength of Acids/BasesStrength of Acids/Bases

pH Scale relates strengths of acids and pH Scale relates strengths of acids and basesbases

pH 0 to 7 – AcidpH 0 to 7 – Acid pH = 7 – NeutralpH = 7 – Neutral pH 7 to 14 – BasepH 7 to 14 – Base pH can only be from 0 to 14pH can only be from 0 to 14 pH= -log[HpH= -log[H++]]

Basic

Acidic Neutral

100

10-

1

10-

3

10-

5

10-

7

10-

9

10-

11

10-

13

10-

14

[H+]

0 1 3 5 7 9 11

13

14

pH

Basic

100

10-

1

10-

3

10-

5

10-

7

10-

9

10-

11

10-

13

10-

14

[OH-]

01357911

13

14

pOH

pHpH

pH= -log[HpH= -log[H++]] Used because [HUsed because [H++] is usually very small] is usually very small As pH decreases, [HAs pH decreases, [H++] increases ] increases

exponentiallyexponentially Sig figs only the digits after the decimal Sig figs only the digits after the decimal

place of a pH are significantplace of a pH are significant [H[H++] = 1.0 x 10] = 1.0 x 10-8-8 pH= 8.00 3 sig figs pH= 8.00 3 sig figs

How to find pHHow to find pH

Punch in calculator: [HPunch in calculator: [H++] or number, log, ] or number, log, +/– +/–

Example: Example: Find pH if [HFind pH if [H++] = 1.0 x 10] = 1.0 x 10-5-5 M M pH = - log(1.0 x 10pH = - log(1.0 x 10-5-5) = 5.00) = 5.00 Punch in + / –, log, 1.0 EXP - 5, Enter Punch in + / –, log, 1.0 EXP - 5, Enter

[H[H++] Concentration] Concentration

If you know the pH, you can determine If you know the pH, you can determine the Molarity of Hthe Molarity of H++ Ions in the solution. Ions in the solution.

Since pH= -log [HSince pH= -log [H++]] Then [HThen [H++] = 10] = 10-pH-pH

What is the Hydrogen Ion concentration What is the Hydrogen Ion concentration of a solution that has a pH of 7.00?of a solution that has a pH of 7.00?

[H[H++] = 10] = 10-7.00-7.00 = 1.0 x 10 = 1.0 x 10-7 -7 MM

How to find [HHow to find [H++]]

Given pH, find [H]; Punch in pH or number, Given pH, find [H]; Punch in pH or number, +/– , 10+/– , 10xx or 2nd log or 2nd log

Example: If pH is 9.0, find [HExample: If pH is 9.0, find [H++] ] pH = -log [HpH = -log [H++] ] Punch in 10Punch in 10xx or 2nd log, +/– , 9.0 or 2nd log, +/– , 9.0 [H] = 1.0 x 10[H] = 1.0 x 10-9-9 M M

What if it has OHWhat if it has OH-- but not but not HH++??

14 = pH + pOH14 = pH + pOH 1.0 x 101.0 x 10-14-14 = [H = [H++] x [OH] x [OH--]] What is the pH of a solution that has a What is the pH of a solution that has a

pOH of 5.00?pOH of 5.00? 14 = pH + 5.00 or 14 – 5.00 = 9.0014 = pH + 5.00 or 14 – 5.00 = 9.00

What would the [HWhat would the [H++] be?] be? [H[H++] = 10] = 10-9.00-9.00 = 1.0 x 10 = 1.0 x 10-9 -9 MM

pOHpOH

Not all substances make [HNot all substances make [H++], some ], some make OHmake OH--

pOH= -log[OHpOH= -log[OH--]] 14 = pH + pOH14 = pH + pOH Sig figs only the digits after the decimal Sig figs only the digits after the decimal

place of a pH are significantplace of a pH are significant [OH[OH--] = 1.0 x 10] = 1.0 x 10-8-8 pOH= 8.00 3 sig figs pOH= 8.00 3 sig figs pH = 14 – 8.00 = 6.00pH = 14 – 8.00 = 6.00

Finding OH- if you have Finding OH- if you have H+H+

• 1.0 x 10-14 = [H+][OH-]1.0 x 10-14 = [H+][OH-]• If you hydrogen ion concentration is If you hydrogen ion concentration is

2.50 x 10-5, what is the Hydroxide ion 2.50 x 10-5, what is the Hydroxide ion concentration?concentration?

• 1.0 x 10-14 = [2.50 x 10-5][OH-]1.0 x 10-14 = [2.50 x 10-5][OH-]• 1.0 x 10-141.0 x 10-14 = [OH-] = [OH-]• 2.50 x 10-52.50 x 10-5 = 4.0 x 10-10= 4.0 x 10-10

IndicatorsIndicators

A solution or compound that changes color A solution or compound that changes color based on pH.based on pH.

Common Indicators:Common Indicators:

Universal Indicator (UI)Universal Indicator (UI)

Methyl RedMethyl Red

Bromothymol BlueBromothymol Blue

Methyl OrangeMethyl Orange