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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