The Chemistry of Acids and Bases

The Chemistry of Acids and Bases

Acids

2

pH below 7turns litmus paper red

taste sour

reacts with metals to produce H2(g)

generally starts with a hydrogen ion

[H+] > [OH-] HCl

3

Bases

pH greater than 7turns litmus paper blue

taste bitter

feel slippery

generally contains a hydroxide ion

[H+] < [OH-] NaOH

4

Both Acids and Bases

an electrolyte

5

Acidic, Basic, and Neutral Solutions

Type of Solutio

n

pH Ranges

[H+] versus [OH-]

Example

Acidic Below 7 [H+] > [OH-]Orange JuiceBattery Acid

Your Stomach

Neutral Equals EXACTLY 7

[H+] = [OH-] DistilledWater

Basic Above 7 [H+] < [OH-]Bleach

Sea WaterBlood

Indicators

Indicators are compounds that have one color in acidic solutions and another in basic.

Litmus Paper

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Copyright © 2007 Pearson Benjamin Cummings. All rights reserved.

Acid Nomenclature Flowchart

BINARY ACIDS

HBr (aq)

Hydrobromic Acid

TERNARY ACIDS

POLYATOMIC IONS

PURE FORMS

TERNARY ACIDS

SO42- H2SO4 H2SO4(aq)

Sulfuric acidSO3

2- H2SO3 H2SO3(aq)

Sulfurous Acid

Naming Ternary Acids

Naming Bases

Use the same rules as for ions (name the cation, then name the anion)

NaOH

Ca(OH)2

KOH

Sodium hydroxideCalcium hydroxide

Potassium hydroxide

polyatomic

Some Common Acids and Bases and their Household Uses.

What are Acids and Bases?

There are two common definitions todescribe acids and bases:

1. Arrhenius acids and bases2. Bronsted-Lowry acids and bases

These are basically the same although they state different things.

Definitions for Acids & Bases

  Arrhenius Brønsted-Lowry

Definition for Acids

   

 

 

Definition for Bases

 

   

 

Key Examples

 

   

 

a proton producer in an aqueous solution

a proton donor

a hydroxide producer in an aqueous solution

a proton acceptor

Acid – HCl

Base - NaOH

Acid – HCl

Base – NH3

H+ = proton

Arrhenius Acids and Bases Definitions

1. Arrhenius Acid

acids in water produce hydronium ions, (H3O+, H+)

HNO3(aq) H+(aq) + NO3-

2. Arrhenius Base

bases in water produce hydroxide ions, (OH-)

KOH(s) K+(aq) + OH-(aq)

HCl + H2O Cl– + H3O+

• Acids are proton (H+) donors. • Bases are proton (H+) acceptors.

conjugate acid

conjugate base

baseacid

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Bronsted-Lowry Definitions

Bronsted-Lowry

Come in Pairs

General equation

HA(aq) + H2O(l) A-(aq) + H3O+(aq)

Acid + Base Conjugate base + Conjugate acid This is an equilibrium.

B(aq) + H2O(l) BH+(aq) + OH-(aq)

Base + Acid Conjugate acid +Conjugate base This is an equilibrium.

What to Focus On?

Arrhenius was the most restrictive definition. This definition required: 

the solutions to be aqueous and  

a base to contain a hydroxide (OH-) ion. 

Bronsted-Lowry’s definition is the most commonly used. It is helpful to remember:

 

acids tend to “lose“ an H+ ion, while

bases tend to “gain“ an H+ ion. 

Under this definition, ammonia (NH3) is considered a base even though it is NOT an Arrhenius base.

Examples HCl(aq) + KOH(s) KCl(aq) + H2O(l)

 

3 Ca(OH)2(aq) + 2 H3PO4(aq) Ca3(PO4)2(s) + H2O(l)

F-(aq) + H2O(l) HF(aq) + OH-(aq)

  HCO3

-(aq) + H2O(l) CO32-(aq) + H3O+(aq)

  NH4

+(aq) + CO32-(aq) NH3(aq) + HCO3

-(aq)

acid base

base acid

base acid

acid base

acid base

conjugate

acid

conjugate

base

conjugate

base

conjugate

acid

conjugate

base

conjugate

acid

Remember Electrolytes?

Na+

NaCl

Na+ Cl-

Cl-

C6H12O6

C6H12O6

C6H12O6

Ionic Covalent

Acids and bases are both strong or weak electrolytes (conduct electricity)• Electrolytes = dissociate (break apart into ions) when dissolved

• Strong = completely Weak = partially Non = not at all

H+

HC2H3

O2

H+

C2H3O21-

C2H3O21- H

+

H-Cl

H+

Cl-

Cl-

Weak Strong

Lots of IonsOnly a few Ions

23

Strong Electrolytes

Notice that all of the ions are separated or dissociated.

WORD DESCRIPTION Completely breaks

apart into its ions Are good conductors

of electricity Will produce a bright

light bulb Examples of Acids and

Bases that are Strong Electrolytes

Strong Acids Strong BasesH2SO4 NaOH

HCl Ba(OH)2

24

Notice that only some of the ions are separated or dissociated.

Weak Electrolytes

WORD DESCRIPTION Partially breaks apart

into its ions Are poor conductors of

electricity Will produce a dim light

bulb Examples of Acids and

Bases that are Weak Electrolytes

Weak AcidHC2H3O2 (Vinegar)

Weak BaseNH3 (Ammonia)

25

Strong BasesThe hydroxides of the

Group I and Group II

LiOH - lithium hydroxide NaOH - sodium hydroxide KOH - potassium hydroxide *Ca(OH)2 - calcium hydroxide

*Sr(OH)2 - strontium hydroxide

*Ba(OH)2 - barium hydroxide

What makes a strong acid or a strong base?

Strong electrolytes make strong acids and bases

Strong Acids

HCl - hydrochloric acid HBr - hydrobromic acid HI - hydroiodic acid HNO3 - nitric acid

H2SO4 - sulfuric acid HClO4 - perchloric acid

pH Concept

pH ScalePouvoir hydrogéne (hydrogen power)

Is a scale to measure the acidity of a sample, Range: 0 -14

1 14

Highly acidic Very basic (not acidic)

neutral

7

Acids 0-7 Bases 7-14Neutral = 7.0

Relationships between pH, [H+], and [OH-]

As pH increases… The [H+] (increases or decreases). The [OH-] (increases or decreases). The solution becomes more (acidic or

basic).

Relationships between pH, [H+], and [OH-]

What happens as pH decreases?

As pH decreases… The [H+] (increases or decreases). The [OH-] (increases or decreases). The solution becomes more (acidic or

basic).

The pH Scale

The value of pH is unitless.

Solutions with a pH less than 7 are acidic and solutions greater than 7 are basic.

If a solution is equal to 7 it is neutral.

Here is a typical pH scale.

pH of Common Substances

pH is a Logarithmic Scale

Logarithm –The number of times a base must be multiplied by itself to reach a given number

yx blog# of multiples

Base

# you’re trying to reach

pH is a Logarithmic Scale

pH Calculations

Given Solving for

Formula to Use

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

[OH-] pOH pOH = - log[OH-]

[H+] is the concentration of H+ ions, in mol/L.

Logarithms

Use your calculator! If you have a log button, you’re all set.

Each calculator can have its own method for entering logs.

If you don’t know what to do your calculator manual should give examples.

+

-1

/

x

0

2 3

4 5 6

7 8 9

.

CE

EE

log

ln

1/x

x2

cos tan

1.44939 E -2

9 - 43

Logarithms

If your calculator has a ln button -

• Don’t use it.• Its for taking natural logs.• This is different than base 10.

+

-1

/

x

0

2 3

4 5 6

7 8 9

.

CE

EE

log

ln

1/x

x2

cos tan

1.44939 E -2

9 - 44

Calculating pH

If [H+] is written in scientific notation and has a coefficient of 1, then the pH of the solution equals the absolute value of the exponent

Ex. 1.0 x 10-4 M

pH = 4.0

Problem 1:

If [H+] = 3.40 x 10-5 M, what is the pH?Given UnknownEquation[H+] = 3.40 x 10-5 M pH pH = - log[H+]

Solve:

pH = -log (3.40 x 10-5)

pH = 4.47

Calculating pH

Problem 2:

If [H+] = 1 X 10-10, what is the pH?

Given Unknown Equation[H+] = 1 X 10-10 pH pH = -

log[H+]

Solve:pH = - log 1 X 10-10

pH = - (- 10)pH = 10

Calculating pH

Problem 3:

If [H+] = 1.8 X 10-5, what is the pH?

Given Unknown Equation[H+] = 1.8 X 10-5 pH pH = -

log[H+]

Solve:pH = - log 1.8 X 10-5

pH = - (- 4.74)pH = 4.74

Calculating pH

Problem 1:If [OH-] = 2.30 x 10-12 M, what is the pOH?

Given Unknown Equation

[OH-] = 2.30 x 10-12 M pOH pOH = - log[OH-]

Solve:pOH = -log (2.3 x 10-12)

pOH = 11.6

Calculating pOH

If [OH-] is written in scientific notation and has a coefficient of 1, then the pOH of the solution equals the absolute value of the exponent

Problem 2:

If [OH-] = 1.0 x 10-9 M, what is the pH?pOH = 9.0

Calculating pOH

WHAT’S IN A GLASS OF WATER?

distilled

Distilled H2O at the Molecular LevelWhat’s in a glass of distilled water?

• Water Molecules (H2O)

• Hydronium Ions (H3O+)• Hydroxide Ions (OH-)

What’s happens in the glass of water?

H2O + H2O H⇆ 3O+ + OH-

This is called the self-ionization of water.

WaterWater ionizes- falls apart into ions.

H2O ® H+ + OH-.

Only a small amount.

[H+ ] = [OH-] = 1 x 10-7M

A neutral solution.

In water Kw = [H+ ] x [OH-] = 1 x 10-14

Kw is called the ion product constant.

pH + pOH = 14Amphoteric

a molecule or ion that can react as an acid as well as a baseEx: H2O, NH3

Calculating pOH from pH

If the pH is 3.25, what is the pOH?Given pH = 3.25

UnknownpOH ?

Equation pH + pOH = 14

Substitute and solve :

3.25 + pOH = 14

3.25 + (- 3.25) +pOH = 14 (- 3.25)

pOH = 10.8

Problem 1:

What is the pH of a solution if [OH-] = 4.0 x 10-11 M?

Given [OH-] = 4.0 x 10-11 M

UnknownpH?

Equation

pH + pOH = 14

Step 1: Find pOHpOH = -log [OH] pOH= -log[4.0 x 10-11 ] = 10.4

Step 2: Calculate pHpH + pOH= 14; pH = 14 – 10.4 pH = 3.6

Calculating pH from pOH

Problem 2:

Looking at the Math

Given Solving for

Formula to Use

pH [H+]

pOH [OH-]pOHOH 10][

pHH 10][

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

[H+] = 10-3.12 = 7.6 x 10-4 M

*** to find antilog on your calculator, look for “Shift” or “2nd function” and then the log button

KnownpH = 3.12

Unknown[H+] ?

Analysis[H+] = 10 -pH

Substitute and solve :

Calculating [H+] from pH

Calculating [H+] from pH

The pH of an unknown solution is 6.00. What is its [H+]?

KnownpH = 6.00

Unknown[H+] ?

Analysis[H+] = 10 -pH

Substitute and solve :

[H+] = 1x 10 -6 M

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

Calculating [H+] from pH

KnownpH = 8.5

Unknown[H+] ?

Analysis[H+] = 10 -pH

Substitute and solve :

[H+] = 10-8.5

3.16 X 10-9 M

Acid-Base Reactions or Neutralization Reactions

acid + base water + salt

1. HBr(aq) + NaOH(aq)

2. H2SO4(aq) + KOH(aq)

3. H3PO4(aq) + Ba(OH)2(aq)

* Double replacement reactions

H2O + NaBr

H2O + K2SO4

H2O + Ba3(PO4)2