The Chemistry of The Chemistry of Acids and BasesAcids and BasesThe Chemistry of The Chemistry of Acids and BasesAcids and BasesCh. 19Ch. 19

Acid and BasesAcid and Bases

Acid and BasesAcid and Bases

Acid and BasesAcid and Bases

Acids

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

HaveHave a bitter taste.a bitter taste.

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

Bases

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”

Acid 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 '

An easy way to remember which goes with which…An easy way to remember which goes with which…““In the cafeteria, you In the cafeteria, you ATEATE something something ICICky”ky”

• HBr HBr (aq)(aq)

• HH22COCO33

• HH22SOSO33

hydrobromic acidhydrobromic acid

carbonic acidcarbonic acid

sulfurous acidsulfurous acid

Acid Nomenclature Review

Name ‘Em!

• HI HI (aq)(aq)

• HCl HCl (aq)(aq)

• HH22SOSO33

• HNOHNO33

• HIOHIO44

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 “Basic Blue”Turns red litmus paper to blue “Basic Blue”

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 “MOM” Milk of

magnesiamagnesia

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

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!)

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

Arrhenius base is a substance that produces OH- in water

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!

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

acidconjugate

basebase conjugate

acid

Conjugate PairsConjugate Pairs

Brønsted – Lowry

• Conjugate Acid – species produced when a base accepts a hydrogen ion from an acid

• Conjugate Base – species that results when an acid donates a hydrogen ion to a base.

• Amphoteric – water and other substances that can act as both acids and bases

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

The Brønsted definition means NHThe Brønsted definition means NH33

is a is a BASEBASE in water — and water in water — and water is itself an is itself an ACIDACID

BaseAcidAcidBaseNH4

+ + OH-NH3 + H2OBaseAcidAcidBase

NH4+ + OH-NH3 + H2O

Brønsted – Lowry

• Polyprotic Acids – can donate more than one hydrogen ion– Examples

• H2CO3 – diprotic acid (can donate 2 H+)

• H3PO4 – triprotic acid (can donate 3 H+)

• Monoprotic Acid – can only donate one hydrogen ion– Examples: HF, HBr, HNO3

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

++

The The pH scalepH scale is a way of is a way of expressing the strength of expressing the strength of acids and bases. Instead acids and bases. Instead of using very small of using very small numbers, we just use the numbers, we just use the NEGATIVE power of 10 NEGATIVE power of 10 on the Molarity of the Hon the Molarity of the H++ (or OH(or OH--) ion.) ion.

Under 7 = acidUnder 7 = acid 7 = neutral 7 = neutral

Over 7 = baseOver 7 = base

pH of Common pH of Common SubstancesSubstances

Calculating the pHpH = - 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

Try These!Try These!

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

1) A 0.15 M solution 1) A 0.15 M solution of Hydrochloric of Hydrochloric acidacid

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

pH 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++] = ??? M] = ??? M

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” *** to find antilog on your calculator, look for “Shift”

or “2or “2nd nd function” and then the log buttonfunction” and then the log button

pH 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++]]

More About WaterMore About WaterHH22O can function as both an ACID and a BASE.O can function as both an ACID and a BASE.

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

Equilibrium constant for water = KEquilibrium constant for water = Kww

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

HONORS ONLY!HONORS ONLY!

More About WaterMore About Water

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

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

so Kso Kww = [H = [H33OO++]]22 = [OH = [OH--]]22

and so [Hand so [H33OO++] = [OH] = [OH--] = 1.00 x 10] = 1.00 x 10-7-7 M M

OH-

H3O+

OH-

H3O+

AutoionizationAutoionization

HONORS ONLY!HONORS ONLY!

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

pH and pOHpH and pOH are opposites! are 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 Since pH and pOH are on

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

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

[H[H33OO++], [OH], [OH--] and ] and pHpH

What is the pH of the What is the pH of the 0.0010 M 0.0010 M NaOH solution? 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

The 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?

[OH[OH--]]

[H[H++]] pOHpOH

pHpH

1010 -pOH

-pOH

1010 -pH-pH-Log[H

-Log[H++]]

-Log[OH

Log[OH

--]]

14 -

pOH

14 -

pOH

14 -

pH

14 -

pH

1.0

x 10

1.0

x 10-1

4-14

[OH[O

H-- ]]

1.0

x 10

1.0

x 10-1

4-14

[H[H

++ ]]

Calculating [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?

pH 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

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

paperpaper

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

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

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

pH paperpH paper

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 a Must be calibrated with a buffer solutionbuffer solution

pH 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

Neutralization

• Neutralization reaction – a reaction in which an acid and base react to produce salt and water

• Salt – an ionic compound made up of a cation from a base and an anion from an acid

Mg(OH)2 + 2HCl MgCl2 + 2H2O

Base + acid salt + water

Titration

• Titration - method for determining the concentration of a solution by reacting a known volume of the solution with a solution of known concentration

• Endpoint – point at which the indicator used in titration changes color

Setup for titrating an acid with a baseSetup for titrating an acid with a base

TitrationTitrationTitrationTitration

1. Add solution from the buret.1. Add solution from the buret.2. Reagent (base) reacts with 2. Reagent (base) reacts with

compound (acid) in solution compound (acid) in solution in the flask.in the flask.

3.3. Indicator shows when exact Indicator shows when exact stoichiometric reaction has stoichiometric reaction has occurred. (Acid = Base)occurred. (Acid = Base)

This is called This is called NEUTRALIZATION.NEUTRALIZATION.

PROBLEM: You have 50.0 mL of PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M 3.0 M NaOH and you want 0.50 M NaOH. What do you do?NaOH. What do you do?

PROBLEM: You have 50.0 mL of PROBLEM: You have 50.0 mL of 3.0 M NaOH and you want 0.50 M 3.0 M NaOH and you want 0.50 M NaOH. What do you do?NaOH. What do you do?

3.0 M NaOH 0.50 M NaOH

H2O

Concentrated Dilute

But how much water But how much water do we add?do we add?

MM11 • V • V11 = M = M22 • V • V22

Preparing Solutions Preparing Solutions by Dilutionby Dilution

Preparing Solutions Preparing Solutions by Dilutionby Dilution

You try this dilution problem

• You have a stock bottle of hydrochloric acid, which is 12.1 M. You need 400 mL of 0.10 M HCl. How much of the acid and how much water will you need?

Buffers• Buffers – resist changes in pH when

limited amounts of acids or bases are added

• How does it work?– Contains mixtures of weak acid and its

conjugate base or weak base and its conjugate acid

– These ions react with added H+ or OH- resisting changes in pH

– Buffer Capacity – amount of acid/base that a buffer can withstand

Buffers

• Used to maintain body pH– Blood pH = 7.4– Variations of 0.3 in pH can cause health

problems• Example: Cramping in your leg muscle while

exercising is a mild case of acidosis caused by the buildup of lactic acid in your muscle tissue.