Antacids: 2B
• This unit will introduce the chemistry needed
to understand how antacids work
Section 2.4: Defining & Naming Acids &
Bases
Section 2.5a Characteristics and pH
calculations
Sections 2.5b Acid-Base Titrations
Section 2.4
We need to know how acids behave when
talking about ant-acids!
What is an Acid? – Arrhenius Definition
• A substance that produces hydrogen ions (H+1)
when dissolved in water.
• H+1 immediately reacts with water to make the
hydronium ion, H3O+1
+1
+1
water
How do Acids produce Hydronium?
water
acid
Hydrogen cation with some anion
How do Acids produce Hydronium?
+1
-
How do Acids produce Hydronium?
+1
Hydronium ion
Anion
How to Identify an Acid
• Look for a hydrogen ion, “H+” as the first
element in an aqueous covalent compound.
These are the 5 you must know:
H2SO4 HCl H2CO3 HNO3 HC2H3O2
Naming Binary Acids: Non-Oxygen Acids
These compounds have to :
Start with “H” (more than 1 “H” is OK, too).
Do not contain oxygen
To name these compounds:
Use “hydro____ic acid”
Fill in the blank with the root of the anion’s name
Example #1
HBr(aq)
It’s an acid
Hydrogen cation
HBr(aq)
Hydrobromic acid
Bromine
No oxygen
Use “hydro___ic”
Naming Oxyacids: contain oxygen
These compounds have:
Start with “H” (more than 1 “H” is OK, too).
Must contain oxygen
To name these compounds:
Use “___ic acids” for “-ate” anions
Use “___ous acids” for “-ite” anions
Do not use “hydro” with these…the word “acid” is how you know it begins
with hydrogen, not “hydro-”
Example #2
HNO2(aq)
It’s an acid
Hydrogen cation
HNO2(aq)
nitrite ion
“-ite” ion
Use “___ous” acid
Nitrous acid
Example #3
HC2H3O2(aq)
It’s an acid
Hydrogen cation
HC2H3O2(aq)
acetate ion
“-ate” ion
Use “___ic”
acetic acid
Self Check
HF
Example:
Write the name
for the following
acids
H2S
H3PO4
Answers
Example:
Write the name
for the following
acids
HF
Hydrofluoric acid
H2S
Hydrosulfuric acid
H3PO4
Phosphoric acid
Writing the chemical formula for “Hydro-”
acids
To write these formulas:
Write the cation, H+1
Write the anion symbol and charge
Balance the charges by adding the appropriate
subscript to the hydrogen cation OR Criss Cross
Method
Example #4
Hydrobromic acid
H+1
Hydrogen cation
Hydrobromic acid
Does not contain oxygen
Br-1
H+1
Hydrogen cation
Hydrobromic acid
Does not contain oxygen
Br-1
H+1Br-1
+1 + -1 = 0
HBr
The compound is neutral.
Subscripts are not needed
Writing chemical formulas for “Oxyacids”
To write these formulas:
Write the cation H+1
If it is an “-ic” acid, determine the polyatomic ion
ending in “-ate”
If it is an “-ous” acid, determine the polyatomic ion
ending in “-ite”
Add subscript to the hydrogen cation to balance
charges OR use Criss Cross Method
Example #5
Carbonic acid
H+1
Hydrogen cation
Carbonic acid
From the “___ate” anion
CO3-2
H+1
Hydrogen cation
H+ CO32+1 + -2 = -1
Carbonic acid
From the “___ate” anion
CO3-2
H2CO3
H+ H+ CO32+1 + 1 + -2 = 0
Example #6
Chlorous acid
H+1
Hydrogen cation
chlorous acid
From the “___ite” anion
ClO2-1
H+1
Hydrogen cation
Chlorous acid
From the “___ite” anion
ClO2-1
H+ClO2-1
+1 + -1 = 0
HClO2
Self Check
Phosphorous acid
Example:
Write the
formula for the
following acids
Hydroiodic acid
Answers
Example:
Write the
formula for the
following acids
Phosphorous acid
H3PO3
Hydroiodic acid
HI
You Really Only Need to Know These
Acids! Memorize them!
•
•
•
•
•
Hydrochloric acid HCl
Sulfuric acid
H2SO4
Carbonic acid
H2CO3
Nitric acid
HNO3
Acetic acid
HC2H3O2
What is a Base? – Arrhenius Definition
• A substance that produces hydroxide ions,
OH-1 in water
H2O
NaOH(s)
Na+1(aq) + OH-1(aq)
+1
-1
Hydroxide Ion
water
How to Identify a Base
• Look for an ionic compound that has a metal
paired with the hydroxide ion, “OH-”
• OR Look for the ammonia molecule
NaOH Ca(OH)2 NH3
**Do not assume all compounds ending in OH are
bases: CH3OH is not a base but an alcohol
Naming & Writing Formulas for Metal Hydroxides
Follow the rules for ionic compounds.
The most common exception to this is ammonia,
NH3
NH3 (ammonia) is a base even though it doesn’t contain
“-OH” as the anion
Example #7
NaOH
Sodium
NaOH
Hydroxide
Sodium Hydroxide
Self Check
Ca(OH)2
Example:
Write the
formula or name
for each
KOH
Copper (II) hydroxide
Lithium hydroxide
Answers
Example:
Write the
formula or name
for each
Ca(OH)2
Calcium hydroxide
KOH
Potassium hydroxide
Copper (II) hydroxide
Cu(OH)2
Lithium hydroxide
LiOH
Another of definition of an ACID:
According to Bronsted-Lowry
 An acid is a hydrogen (proton) donor
 The substance that remains after the hydrogen
has been donated is called the conjugate base
Example: NH3 + H2O 
acid
OH-
conjugate base
+ NH4+
Another definition of a BASE:
According to Bronsted-Lowry
 A base is a hydrogen (proton) acceptor
 The substance that forms after the hydrogen
has been accepted is called the conjugate aci
Example: NH3 + H2O 
base
OH-
+ NH4+
conjugate acid
Bronsted-Lowry: The Big Picture
Conjugate Acid-Base Pairs
•
•
•
ACIDS & BASES WILL ALWAYS BE ON THE REACTANT
SIDE
CONJUGATE ACIDS & BASES WILL ALWAYS BE ON THE
PRODUCT SIDE
Practice Problems: Label the acid & base on the left side of the
reaction and the conjugate acid & conjugate base on the right side.
a) HCl + H2O  H3O+ + Cl−
______
acid ______
base ______
C.A. ______
C.B.
b) HCO3-1 + H2O  H2CO3 + OH−
_____
acid ______
base ______
C.A. ______
C.B.
Section 2.5a:Characteristics & pH
We need to know how acids behave when
talking about ant-acids!
Characteristics of Acids & Bases
Acids
Bases
Produce H3O+1 (hydronium ion)
in water
Produce OH-1 (hydroxide ion) in
water
Tastes sour
Tastes Bitter
React with active metals to
form hydrogen gas
Feels slippery
Neutralizes a base to form salt
and water
Neutralizes an acid to form salt
and water
Both forms ions when dissolved: conducts electricity: They are called
ELECTROLYTES
Section 2.5
Strength versus Concentration
• strong acid – ALL acid molecules separate
(dissociate) into [H+] ions in water; only ions
present
Examples: HCl, HNO3, H2SO4
• weak acid – Most acid molecules stay together,
only a FEW separate into [H+] ions when in water;
few ions present, mostly molecules
Examples: HC2H3O2 (vinegar) , H2CO3
Strong Acid
Weak Acid
Strong versus Weak Acids
-
-
How many hydronium ion – anion pairs
can you find?
3
+
-
How many intact acid molecules can
you find?
1
Strong acid
Most of the acid molecules have
donated the H+1 to water
Strong versus Weak Acids
How many hydronium ion – anion pairs
can you find?
+
1
How many intact acid molecules can
you find?
3
-
Weak acid
Only a few of the acid molecules
have donated the H+1 to water
Strong Acids vs. Weak Acids
Concentrated versus Dilute
solute
solvent
DILUTE
(low concentration)
CONCENTRATED (higher
concentration)
Very little solute (what’s being
dissolved) particles in solution
Lots of solute (what’s being dissolved)
particles in solution
Combinations of Concentration & Strength
Concentrated
Dilute
Strong
A lot of acid/base
added & all
dissociates
Not much acid/base
added, but all of
what’s there
dissociates
Weak
A lot of acid/base
added, but little
dissociates
Not much acid/base
added and very little
dissociates
Bases Strength & Concentration
Bases follow the same pattern as acids
A common misconception is acids are
dangerous but bases are not!
Vinegar is an acid we eat…some of them are safe!
Sodium hydroxide is a very caustic base…not all of
them are less harmful than acids!
The stronger and acid or base is & the more
concentrated it is), the more dangerous it is for you!
Acids and Bases are Electrolytes
Acids and bases
break apart
into ions when
dissolved in
water
Free-floating
ions in water
conduct
electricity
Acids & Bases are
ELECTROLYTES
Strong acids and bases are strong electrolytes
- They produce lots of ions
Weak acids and bases are weak electrolytes
-they don’t produce lots of ions
The Power of the Hydrogen: pH
The pH scale to measure the acidity of a
sample
Acids have a pH that are less than 7.0
Bases have pH values that are more than 7.0
Neutral is considered a pH of 7.0
Ways to measure pH
 Indicators change color based on pH
Liquid indicators – phenolphthalein or bromothymol blue
Bromothymol Blue: Acid: turns Yellow Base: turns blue
Phenolphthalein: Acid: stays clear Base: turns pink
Acid
Base
 pH meters or pH probes
Electronically determine pH and give a read-out
Ways to Measure pH
 Indicators change color based on pH
Paper with a liquid indicator on it (pH paper or Litmus paper)
pH paper turns a color which matches
to a pH number
LITMUS PAPER (Mnemomic: See board!)
 Blue Litmus stays blue in a base
but turns pink in an acid
 Red Litmus stays red in an acid
but turns blue in a base
Practice Questions
1. Which of the following is an Arrhenius Acid?
a. CuOH
b. NH3
c. HC2H3O2
d. CaS
2. Which of the following substances has a bitter
taste and slippery feel?
a. CH3OH
b. NH3
c. HC2H3O2 d. K2S
Practice Questions
3. Which of the following has a pH of 4?
a. NaOH
b. SO2
c. baking soda
d. H2SO4
4. Which of the following substances will cause
red litmus to turn blue?
a. NaCl
b. KOH
c. H3PO4
d. H2CO3
Practice Questions
5. Which of the following will neutralize an acid?
a. NaOH
b. CH4
c. CaF2
d. HNO2
6. Which of the following substances will
increase the number of hydroxide ions in
solution?
a. Fe2O3
b. H2SO4
c. NH3
d. H2CO3
Calculating pH
pH scale – Logarithmic scale of the acidity
of a solution
pH has no units
The pH scale uses base “10”
The formula for calculating pH
The formula for calculating
hydronium ion concentration
pH   log[ H 3O 1 ]
[ H 3O 1 ]  10  pH
[ ] = concentration in
Molarity
The “-” in the pH equation
Because pH is the negative log of concentration of hydronium, as
concentration increases, the pH goes down.
The lowest pH is the highest concentration of hydronium ion
Concentration of Hydronium ion versus pH
[H3O+]
1
0.5
0
0
0.5
1
pH
1.5
2
What does a “log” scale really
mean?
Every change of 1 in pH shows a change of 10x in concentration of hydronium
Level of acidity increases
pH
4
3
2
1
10x
more
acidic
100x
more
acidic
1000x
more
acidic
Example
• The pH of a solution changes from a pH of 5 to
a pH of 3.
a. Did it increase or decrease in hydrogen ion
concentration?
b.By what factor did it change?
Example 2 :Calculating pH
Example:
Find the pH if the
concentration of [H3O+1] is
1.0x 10-8 M
An example of calculating pH
Example:
Find the pH if the
concentration of
[H3O+1] is 1.0 x 10-8 M
pH   log[ H 3O 1 ]
pH   log( 1.0e  8)
pH = 8.00
Example 3; Calculating hydronium
concentration ([H3O+1])
Example:
Find the [H3O+1] if
the pH is 5.0
An example of calculating
hydronium
Example:
Find the [H3O+1] if
the pH is 5.0
[ H 3O 1 ]  10  pH
[ H 3O 1 ]  10 5
H3O+1 = 1 x 10-5 M
Auto-ionization of Water
• Water molecules collide spontaneously
and will split into ions. This is called autoionization
H2O + H2O  H3O+1 + OH-1
• At 25°C the following is true:
[H3O+1] × [OH-1] = 1.0 × 10-14 M2
Hydrogen Ion Concentration Values
• If the hydrogen ion concentration is greater than
hydroxide ion, the solution is ACIDIC with a pH < 7
– [H+] > [OH-] or
– [H+] > 1.0 x 10-7 M
• If the hydrogen ion concentration is less than hydroxide
ion, the solution is BASIC with a pH > 7
– [H+] < [OH-] or
– [H+] < 1.0 x 10-7 M
• If the hydrogen ion concentration is equal to hydroxide
ion, the solution is NEUTRAL with a pH = 7
– [H+] = [OH-] = 1.0 x 10-7 M
Calculating pOH
The formula for calculating pOH
pOH   log[ OH 1 ]
[ ] = concentration in
Molarity
The formula for calculating
hydroxide ion concentration
To relate pH and pOH
[OH 1 ]  10 pOH
pOH  pH  14
Let’s Practice #1
Example:
Find the pOH if the
concentration of [OH-1] is
1.0 × 10-5 M
Let’s Practice #1
Example:
Find the pOH if the
concentration of [OH-1]
is 1.0 × 10-5 M
-1
pOH = -log[ OH ]
-5
pOH = -log(1.0 ´10 M)
pOH = 5.00
Let’s Practice # 2
Example:
Find the pOH if the
pH is 4.
Let’s Practice #2
Example:
Find the pOH if the
pH is 4.
4  pOH  14
pOH= 10
Let’s Practice #3
Example:
Find the [OH-1] if the
[H+] is 1.0 x10-9M
Let’s Practice #3: 2 ways to do
this…
1st way
1
1
[ H 3O ]  [OH ]  110
9
1
14
[1.0 10 ]  [OH ]  110
Example:
Find the [OH-1] if the
[H+] is 1.0 x10-9
14
1

10
[OH 1 ] 
9
[1.0 10 ]
[OH-] = 1.0 x10-5 M
14
Let’s Practice #3:
2 ways to do this… pH   log[ H O 1 ]
3
2nd way
pH = -log(1.0e - 9)
Example:
Find the [OH-1] if the
[H+] is 1.0 x10-9
pH = 9.00
pOH  pH  14
pOH + 9.00 = 14
pOH = 5.00
[OH 1 ]  10 pOH
[OH -1 ] =10-5
[OH-] = 1.0 x10-5 M
Let’s Practice #4
Example:
What is the pH if the
concentration of [OH] = 1.0 x 10-7M
Let’s Practice #4
Example:
What is the pH if the
concentration of [OH-] =
1.0 x 10-7
pOH   log[ OH 1 ]
pOH   log[ 1.0 x107 ]
pOH = 7
pOH  pH  14
7  pH  14
pH = 7
Section
Section 2.5B
Acid- Base
Titrations
Titrations—Using Stoichiometry
Titration – A technique where the
addition of a known volume of a known
concentration solution to a known
volume of unknown concentration
solution to determine the concentration.
•Use a buret to titrate unknown
concentration of solutions.
Titrations—Using Stoichiometry
The titrant is the known concentration
in the buret and the analyte is the
unknown concentration in the flask.
Formula: naMaVa = nbMbVb
na= number of H+ in the acid formula
nb= number of OH- in the base formula
Ma= molarity of acid
Mb= molarity of base
V= volume
End Point vs. Equivalence Point
Equivalence Point (or Stoichiometric
Point)
– When there are no reactants left over—they
have all been reacted and the solution
contains only products
- the point where the acid and the base are
equal in equal moles
moles acid = moles base
Importance of Indicators
Indicators – Paper or liquid that change color based on pH
level.
End Point: point at which the indicator in the solution
changes color
It signals the equivalence point and the stop of the
titration
• Always select an indicator that has a pH
value close to that of the pH of the
equivalence point of the titration.
Titration Process
Titration Problem #1
• How many liters of 0.10 M NaOH is
needed to react with 0.125 L of 0.25 M
HCl?
Titration Problem #2
• What is the molarity of a Ca(OH)2 solution
if 30.0 ml of the solution is neutralized by
20.0 ml of a 0.50 M solution of HCl?
Titration Problem #3
• What volume of 2.0M solution of NH4OH is
needed to neutralize 50.0 ml of a 0.50M
solution of H2SO4?
Titration Curves
 Shows the changes of
pH during a titration
Strong Base - Strong Acid
Weak Base - Strong Acid
 Identifies the pH of the
equivalence point
Strong Base - Weak Acid
Weak Base - Weak Acid
Titration curve for
Titrating a strong acid with a strong base
pH is always = 7
The titration curve graph shows the pH of the
equivalence point. Take the vertical region and cut
the length in half and then look to what pH value
aligns to that point.
Titration curve for
Titrating a strong base with an strong acid
pH is always = 7
Titration curve for
Titrating a weak acid with an strong base
pH is >7