Chapter 15 - Acids & Bases

Acids and Bases

Chapter 14

Outline

I. Properties II. Definitions

A. Arrhenius

B. Brønsted-Lowry

2

Acids

Arrhenius acids

• produce H+ ions in water

H₂O

HCl(g) H+(aq) + Cl _(aq)

• are electrolytes

• have a sour taste • turn litmus red

Bases

Arrhenius bases

• _{produce OH}− ions in

water

• _{taste bitter or chalky} • _{are electrolytes}

• _{feel soapy and} slippery

Hydronium Ion

In water, a dissociated proton (H+) bonds to a

water molecule to form a hydronium ion, H₃O+

Br

nsted-Lowry Acids and Bases

According to the Brønsted-Lowry theory, • _{an acid donates a proton (H}+)

Arrhenius Brønsted-Lowry Acid Forms H+ in solution proton donor

Base _{Forms OH} _{in solution} proton acceptor

Lewis Acid: electron pair acceptor.

Lewis Base: electron pair donor.

8

NH

, A Br

ø

nsted-Lowry Base

In the reaction of ammonia (NH₃) and water,

• NH₃ acts as a base that accepts H+

• H₂O acts as an acid that donates H+

Conjugate Acid-Base Pairs

In an acid-base reaction, there are two conjugate acid-base pairs:

• an acid donates H+ to form its conjugate base • a base accepts H+ to form its conjugate acid

• each is related by the loss and gain of H+ • _{conjugate acid-base pair 1}

10

Conjugate Acid-Base Pairs

In this proton-transfer reaction,

• the conjugate acid-base pairs are NH₄+/NH 3

Learning Check

A. Write the conjugate base of the following: 1. HBr

2. H₂S 3. H₂CO₃

B. Write the conjugate acid of the following: 1. NO₂

Acid Nomenclature

•

_{Binary Acids}

•

HX hydrogen _____ide

– _becomes

Oxyacids of Nitrogen and Sulfur

Nitrogen and sulfur each form two oxyacids (acids with polyatomic atoms with oxygen) that are

named by changing the end of the

• polyatomic ion ate to ic acid (common form)

• polyatomic ion ite to ous acid

NO₃− nitrate ion HNO

3 nitric acid

NO₂− nitrite ion HNO

2 nitrous acid

SO₄2− sulfate ion H

16

Naming Carboxylic Acids

Carboxylic acids are named

• _{in IUPAC by replacing the e in the alkane name with}

oic acid

• _{as common names by using prefixes: form, acet,}

propion, and butyr

H─COOH methanoic acid formic acid

CH₃─COOH ethanoic acid acetic acid

CH₃─CH₂─COOH propanoic acid propionic acid

18

Example of Naming Carboxylic Acids

State the IUPAC and common names of the following:

CH₃—CH₂—CH₂—COOH

4 3 2 1

Learning Check

Give IUPAC and common names for each of the following:

A. CH₃─COOH

20

Some Common Bases

• _{A base with OH} _{ions is named as the}

hydroxide of the metal in the formula. NaOH sodium hydroxide

• _{A strong acid ionizes (100%) in aqueous solutions}.

HCl(g) + H₂O(l) H₃O+ (aq) + Cl- (aq)

• A weak acid dissociates only slightly in water to form an aqueous solution containing mostly molecules of acid and a few ions.

H₂CO₃(aq) + H₂O(l) H₃O+(aq) + HCO

3− (aq)

22

Strong acids

• _{make up six of all the acids} • _{have weak conjugate bases} • _{“–ic” acids. No “–ous”}

Weak acids

• _{make up most of the acids} • have strong conjugate bases

24

Strong Bases

Strong bases

• _{are formed from metals of} Groups 1A (1) and 2A (2) • _{include LiOH, NaOH, KOH,}

and Ba(OH)₂

• _{dissociate 100% in water}

KOH(s) K+(aq) + OH−(aq)

Weak Bases

Weak bases

• _{are poor acceptors of protons} • _{dissociate only slightly in water} • _{produce only a few ions in water} • _{are used in household products}

such as cleaners

26

Learning Check

Identify each of the following as a strong or weak acid or base:

Strong Acids

In water, a strong acid • _{dissociates into ions} • _{produces high}

concentrations of H₃O+

-28

Weak Acids

In a weak acid,

• _{equilibrium favors the}

undissociated (molecular) form of the acid

• the concentrations of H₃O+

and anion A- are low

HA(aq) + H₂O(l)

Acid Dissociation Constant

A weak acid has

• _{an equation for dissociation written}

HA(aq) + H₂O(l) H₃O+(aq) + A(aq)

• _{an equilibrium expression of} K_eq = [H₃O+][A_]

[HA][H₂O]

30

Acid and Base Dissociation

Writing a

K

for a Weak Acid

Write the K_a for H₂S.

1. Write the equation for the dissociation of H₂S. H₂S(aq) + H₂O(l) H₃O+(aq) + HS−(aq)

2. Set up the K_a expression K_a = [H₃O+][HS-]

32

Learning Check

Write the K_a for the weak acid HCN.

In the ionization of water,

• H+ is transferred from one H

2O molecule to another

• _{one water molecule acts as an acid, while another} acts as a base

H₂O(l) + H₂O(l) H₃O+(aq) + OH−(aq)

34

Pure Water is Neutral

In pure water,

• _{the ionization of water}

molecules produces small, but equal quantities of H₃O+ and

OH− ions

• _{molar concentrations are}

indicated as [H₃O+] and [OH−]

[H₃O+] = 1.0 x 10−7 M

Acidic Solutions

Adding an acid to pure water

• increases the [H₃O+]

• causes the [H₃O+] to

exceed 1.0 x 10−7 M

36

Basic Solutions

Adding a base to pure water

• _{increases the [OH}−]

• _{causes the [OH}−] to

exceed 1.0 x 10−7M

38

The ion product constant, K_w, for water • _{is the product of the concentrations of the}

hydronium and hydroxide ions

K_w = [ H₃O+] [ OH− ]

• _{is obtained from the concentrations in pure water}

K_w = [H₃O+][OH−]

K_w = [1.0 x 10−7 M][ 1.0 x 10−7 M]

= 1.0 x 10−14

Ion Product Constant

Example of Calculating [H

O

]

What is the [H₃O+] if [OH−] is 5.0 x 10−8 M?

STEP 1 Write the K_w for water.

K_w = [H₃O+ ][OH− ] = 1.0 x 10−14

STEP 2 Solve the K_w for the unknown [H₃O+].

K_w = [H₃O+ ][OH−]

[OH−] [OH−]

40

Example of Calculating [H

O

]

(continued)

STEP 3 Substitute the known [OH−] and

calculate.

[H₃O+] = 1.0 x 10−14 = 2.0 x 10−7 M

If lemon juice has [H₃O+] of 2.0 x 10−3 M, what is

the [OH−] of the solution?

The [OH−] of an ammonia solution is 4.0 x 10−2

M. What is the [H₃O+ ] of the solution?

Example - K

_w

•

_{If the proton ion concentration of vinegar is}

2.1 x 10

M at 25 °C, what is the

What does the pH scale tell us?

•

_{pH = 7}

_

_neutral

Testing the pH of Solutions

The pH of solutions is determined by using • a pH meter,

• pH paper, or

46

Mathematically,

pH

is the negative logarithm

(log) of the hydronium ion concentration.

pH = -log [H

O

]

For a solution with [H

O

] = 1 x 10

pH = −log [1 x 10

]

pH = [4.0]

pH = 4.0

Decimal Places in pH Values

When expressing pH values, the number of decimal places is equal to the number of

significant figures in the coefficient of [H₃O+].

coefficient decimal places

[H₃O+] = 1 x 104 pH = 4.0

[H₃O+] = 8.0 x 106pH = 5.10

48

Find the pH of a solution with a [H₃O+] of 1.0 x 10−3.

STEP 1 Enter the [H₃O+] value.

1.0 [EE or EXP] 3 [+/] Display: 1−03 or 103

STEP 2 Press the log key and change the sign. [log (1 x 10−3)] [+/] = 3

STEP 3 Adjust the number of significant figures on the right of the decimal point to equal the SFs in the coefficient

1.0 x 10−3 3.00

2 SFs 2 SFs on the right of the decimal point

• The [H₃O+] of tomato juice is 2.2 x 10−4 M.

What is the pH of the solution?

• _{Calculate the pH of a solution with [OH}−] of 4.0

x 10−5.

– Must calculate [H₃O+_{] first!}

50

pOH

The pOH of a solution

• _{is analogous to the pH value on the pH scale.} • _{is based on the [OH}−]

• _{has high pOH values with low [OH}−] and high

[H₃O+]

• _{is equal to the - log [OH}−] pOH = - log [OH−]

Example of Calculating pOH

Calculate the pOH of a solution that has a pH of 8.35. pH + pOH = 14.00

52

Calculating [H

O

] from pH

The [H₃O+] can be expressed by using the pH as

the negative power of 10. [H₃O+] = 10−pH

Example of Calculating

[H

O

] from

pH

•

Calculate the [H

O

] for a pH value of 8.0.

•

What is the [H

O

] of a solution with a pH of

3.80?

•

_{What is the pH and the pOH of coffee if the}

54

Identify each solution as

A) acidic, B) basic, or N) neutral. 1. ___ HCl with a pH = 1.5

2. ___ pancreatic fluid [H₃O+] = 1 x 10−8 M

3. ___ soft drink pH = 3.0 4. ___ pH = 7.0

5. ___ [OH−] = 3 x 10−10 M

6. ___ [H₃O+ ] = 5 x 10−12

Classify each of the following foods

as acidic, basic or neutral

•

egg white, pH = 7.9

•

maple syrup, pH = 7.0

•

_{champagne, pH = 3.8}

•

_{sour milk, pH = 6.2}

•

_{lime juice, pH = 1.8}

Example – pH and pOH

[H

O

]

[OH

]

pH

pOH

5.98 x 10

M

9.63 x 10

M

9.092

1. Reactivity with Metals

2 HCl (aq) + Mg (s) MgCl₂ (s) + H₂ (g) Acids react with any metals above

hydrogen in the activity series.

In general:

acid + metal salt + hydrogen

2. Reactivity with Bases

2 HCl (aq) + Ca(OH)₂ (aq) CaCl₂ (aq) + 2 H₂O (l) Also called a neutralization reaction.

3. Reactivity with Metal Oxides

2 HCl (aq) + Na₂O(s) 2 NaCl (aq) + H₂O (l)

In general:

acid + metal oxide salt + water

4. Reactivity with Metal Carbonates

2 HCl (aq) + Na₂CO₃ (aq) 2 NaCl (aq) + H₂O (l) + CO₂ (g)

acid + carbonate salt + water + carbon dioxide

(base)

In general:

(base)

© 2014 John Wiley & Sons, Inc. All rights reserved.

Acids and Metals

Acids react with metals

• such as K, Na, Ca, Mg, Al, Zn, Fe, and Sn

• to produce hydrogen gas and the salt of the metal Chemical equations

2K(s) + 2HCl(aq) 2KCl(aq) + H₂(g) Zn(s) + 2HCl(aq) ZnCl₂(aq) + H₂(g)

Net ionic equations

60

Acids and Carbonates

Acids react with carbonates and hydrogen

carbonates to produce carbon dioxide gas, a salt, and water.

Learning Check

Write the products of each of the following

reactions as the complete equation and the net ionic equation:

A. Zn(s) + 2 HCl(aq)

62

• _{In the chemical and net ionic equations for}

neutralization, an acid and a base produce a salt and water.

acid base salt water

HCl(aq) + NaOH(aq) NaCl(aq) + H₂O(l) H+(aq) + OH−(aq) H

2O(l)

2HCl(aq) + Ca(OH)₂(aq) CaCl₂(aq) + 2H₂O(l) 2H+(aq) + 2OH−(aq) 2H

2O(l)

Antacids

64

Predict the products and then balance the following neutralization equations:

HCl (aq) + Al(OH)₃(s)

Ba(OH)₂(aq) + H₃PO₄(aq)

Salts That Form Neutral Solutions

A salt solution containing the ions of a strong acid and a strong base

• _{forms a neutral solution}

• _{does not produce or attract H}+ from water

Example:

KNO₃ forms a neutral solution because it contains a cation (K+) from a strong base (KOH) and an

anion (NO₃_{) from a strong acid (HNO}

66

Salts That Form Basic Solutions

A salt solution containing ions of a weak acid and strong base

• _{forms a basic solution}

• _{has an anion of the weak acid that attracts H}+ from

water

Example:

KHCO₃ forms a basic solution because its anion forms a weak acid (H₂CO₃), but its cation is from strong base (KOH).

HCO₃_{(aq) + H}

2O(l) H2CO3(aq) + OH(aq)

Salts That Form Acidic Solutions

A salt solution containing ions of a strong acid and a weak base

• _{forms an acidic solution}

• has a cation of the weak base that produces H+ in

water

Example:

NH₄Cl forms an acidic solution because it has the cation of a weak base (NH₃) and an anion of the strong acid (HCl)

68

Cations and Anions of Salts for

70

Learning Check

Predict whether a solution of each salt will be (A) acidic, (B) basic, or (N) neutral.

1. Li₂S (aq)

Example - pH

•

_{Find the pH of coffee when the hydrogen}

Example - pH

•

_{Calculate the pH of carrot juice with a}

hydronium ion, [H

O

], concentration of 7.9

Example - pH

•

A bottle of table wine has [H

O

] = 3.2 x

10

M. After one month the [H

3

O

] rises to

1.0 x 10

M. Calculate the pH of the new

Example - pH

•

Calculate the hydronium ion, [H

O

],

Example - pOH

A. What is the pOH of a solution that is 2.57

Example - pOH

A. What is the pOH of a solution that is 2.57



10

M in NaOH?