Strong
Acids and
Bases
We’ll show you what strong acids and bases are and how to find them.
Strong
Acids
Let’s start with strong acids.
A Strong Acid is an acid that is
100% ionized in water.
A Strong Acid is an acid that is 100% ionized in water.
A Strong Acid is an acid that is
100% ionized in water.
A Strong Acid is an acid that is
100% ionized in aqueous solution.
Or we could also say: A Strong Acid is an acid that is 100% ionized in aqueous solution.
A Strong Acid is an acid that is
100% ionized in aqueous solution.
HCl (g)  H 2O( l ) 
Strong
Acid
For example, one strong acid is HCl.

H 3O(aq)


Cl (aq)
A Strong Acid is an acid that is
100% ionized in aqueous solution.
HCl (g)  H 2O( l ) 
Strong
Acid
When HCl is added to water.

H 3O(aq)


Cl (aq)
A Strong Acid is an acid that is
100% ionized in aqueous solution.
HCl (g)  H 2O( l ) 
Strong
Acid
It completely ionizes

H 3O(aq)


Cl (aq)
A Strong Acid is an acid that is
100% ionized in aqueous solution.
HCl (g)  H 2O( l ) 
Strong
Acid
To form a hydronium ion

H 3O(aq)


Cl (aq)
A Strong Acid is an acid that is
100% ionized in aqueous solution.
HCl (g)  H 2O( l ) 
Strong
Acid
And a chloride ion.

H 3O(aq)


Cl (aq)
A Strong Acid is an acid that is
100% ionized in aqueous solution.
HCl (g)  H 2O( l ) 
Strong
Acid

H 3O(aq)


Cl (aq)
Single
arrow
means
100 %
The single arrow pointing to the right here means that the reaction goes to completion, or
100%.
HCl (g)  H 2O( l ) 

H 3O(aq)


Cl (aq)
[I]
[C]
[F]
We can illustrate 100% ionization using what is called an I C F table. I is initial concentration, C is the change in
concentration as the reaction takes place, and F is the final concentration after the reaction is complete.
HCl (g)  H 2O( l ) 

H 3O(aq)


Cl (aq )
[I]
[C]
[F]
Because we have a water solution, any changes in the amount of water due to the
reaction will be irrelevant, so we ignore the column corresponding to water.
HCl (g)  H 2O( l ) 
[I]

H 3O(aq)


Cl (aq)
1.0
[C]
[F]
If we add 1.0 mol of HCl to enough water to make 1.0 Litre of solution, the initial
concentration of HCl will be 1.0 molar.
HCl (g)  H 2O( l ) 
[I]
1.0

H 3O(aq)
0


Cl (aq)
0
[C]
[F]
And the concentrations of hydronium and chloride ions are initially zero
HCl (g)  H 2O( l ) 
[I]
1.0

H 3O(aq)
0
[C]
[F]
Immediately the reaction (click) will proceed to the right


Cl (aq)
0
HCl (g)  H 2O( l ) 
[I]
1.0
[C]
–1.0

H 3O(aq)
0


Cl (aq)
0
[F]
As it’s proceeding to the right, all of the HCl molecules will ionize. So the concentration
of HCl molecules will go down by 1.0 M.
HCl (g)  H 2O( l ) 

H 3O(aq)


Cl (aq)
[I]
1.0
0
0
[C]
–1.0
+1.0
+1.0
[F]
And because the coefficients on HCl, hydronium and chloride are all 1, as the reaction proceeds
to the right, the concentrations of hydronium and chloride ions both go up by 1.0 M
HCl (g)  H 2O( l ) 

H 3O(aq)


Cl (aq)
[I]
1.0
0
0
[C]
–1.0
+1.0
+1.0
[F]
0
So the final concentration of HCl molecules will be 1 minus 1, which is equal to zero
HCl (g)  H 2O( l ) 

H 3O(aq)


Cl (aq)
[I]
1.0
0
0
[C]
–1.0
+1.0
+1.0
[F]
0
1.0
1.0
And the final concentrations of hydronium and chloride ions will both be 1.0 M. So 100% of the
original HCl molecules have been ionized to form hydronium and chloride ions.
HCl (g)  H 2O( l ) 

H 3O(aq )


Cl (aq)
[I]
1.0
0
0
[C]
–1.0
+1.0
+1.0
[F]
0
1.0
1.0
If we focus on hydronium ions we can see that the final concentration of hydronium is equal
to the initial concentration of the strong acid. This is true for all strong acids.
HCl (g)  H 2O( l ) 

H 3O(aq )


Cl (aq)
[I]
1.0
0
0
[C]
–1.0
+1.0
+1.0
[F]
0
1.0
1.0
For a strong acid:
[H3O+] = [acid](I)
So we can write an equation here. For any strong acid, the concentration of hydronium is equal
to the initial concentration of the acid.
For a strong acid:
[H3O+] = [acid](I)
In 6.0 M HCl
+
[H3O ] = 6.0 M
labelled
So if we have a solution that is labelled as 6.0 M hydrochloric acid.
For a strong acid:
[H3O+] = [acid](I)
In 6.0 M HCl
+
[H3O ] = 6.0 M
Because hydrochloric acid is a strong acid, we know that the concentration of hydronium in
this solution is 6.0 M.
Which acids are
strong acids?
The question now is, which acids are strong acids?
Strong Acids
are the
Top 6 acids on
the Left Side
Looking at the acid table, the strong acids are the top 6 acids on the left side of the table. On
many tables, the region these occupy is shaded.
Ionizations of
strong acids
all have single
arrows.
Notice that the ionization equations for strong acids all have single arrows pointing to the
right. This is a further indication that strong acids are 100% ionized.
Ka’s are all
“very large”
Ka is the equilibrium constant for the ionization of an acid. For strong acids, the ionizations
are essentially complete, which means the equilibrium constant is very large.
Electrical
Conductivity of
Strong Acids
Electrical conductivity of strong acids.
The conductivity of a solution
depends on the total ion
concentration in the solution.
It is known that the conductivity of a solution depends on the total ion concentration in the
solution.
The conductivity of a solution
depends on the total ion
concentration in the solution.
Strong acids completely ionize
in water, so unless they are
very dilute, they produce a
high concentration of ions.
Strong acids completely ionize in water
The conductivity of a solution
depends on the total ion
concentration in the solution.
Strong acids completely ionize
in water, so unless they are
quite dilute, they produce a
high concentration of ions.
so unless they are quite dilute,
The conductivity of a solution
depends on the total ion
concentration in the solution.
Strong acids completely ionize
in water, so unless they are
quite dilute, they produce a
high concentration of ions.
they produce a high concentration of ions.
water
If we had a beaker with pure water
water
And we inserted a conductivity apparatus, the bulb would not glow because water
consists almost entirely of neutral H2O molecules and has very few ions in solution.
HNO3
Now we’ll add enough of the strong acid (click), HNO3 to this beaker,
HNO3
To make the concentration of HNO3 0.1 molar
0.1 M
– 0.1 M
+
HNO
NO
3
H3O
3
The strong acid HNO3 will immediately and completely ionize into hydronium and
nitrate ions. Notice the light bulb glows to show that we now have high conductivity.
H3O+
NO3–
0.1 M
Because the concentration of (click) HNO3 was 0.1 M, the resulting concentrations of
hydronium and nitrate will both be 0.1 M
Total ion concentration
= 0.1 M + 0.01 M = 0.2 M
H3O+
0.1 M
NO3–
0.1 M
So this means that the total ion concentration in the beaker is equal to
Total ion concentration
= 0.1 M + 0.1 M = 0.2 M
H3O+
0.1 M plus 0.1 M
0.1 M
NO3–
0.1 M
Total ion concentration
= 0.1 M + 0.1 M = 0.2 M
H3O+
0.1 M
NO3–
0.1 M
Which is 0.2 M. An ion concentration of 0.2 M is high enough to account for the high
conductivity of this solution.
We’ll represent all
strong acids by
the formula HA.
We’ll represent all strong acids by the formula HA.
We’ll represent all
strong acids by
the formula HA.
All strong acids
(HA) ionize 100%
H3O+
A–
All strong acids, HA, ionize 100% into hydronium and A minus ions.
We’ll represent all
strong acids by
the formula HA.
All strong acids
(HA) ionize 100%
H3O+
Which make the light bulb glow.
A–
All strong acids
ionize 100%
H3O+
A–
A conducting solution is called an electrolyte. Because all strong acids ionize 100% in
solution,
Strong acids are
strong
electrolytes
All strong acids
ionize 100%
H3O+
A–
We can generalize and say that strong acids are strong electrolytes.
Strong
Bases
Now we’ll talk about strong bases.
A Strong Base is a base that
dissociates 100% in aqueous
solution.
A Strong Base is a base that dissociates 100% in aqueous solution.
A Strong Base is a base that
dissociates 100% in aqueous
solution.
We use the word dissociates rather than ionizes for strong bases.
e.g. NaOH(s)
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+
Strong bases consist of ionic compounds. An example is sodium hydroxide, NaOH. We can
show it roughly here as a crystal lattice of sodium and hydroxide ions.
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+
When a piece of solid NaOH is placed in water, the polar water molecules attract the ions (click)
and pull them away from the crystal.
Na+
OH–
Na+
OH–
Dissociation
Na+ OH– Na+
OH–
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+
This process is called (click) dissociation
NaOH(s) 

Na(aq)

Dissociation of NaOH
The dissociation of NaOH can be depicted by this equation

OH(aq)
NaOH( s) 

Na(aq)


OH( aq)
This is actually a
crystal lattice of
Na+ and OH– ions
You need to be aware that even though the formula for solid NaOH looks like a molecular formula, it is
actually an empirical formula which represents a crystal lattice of Na+ and OH minus ions.
NaOH( s) 
Like this.
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+

Na(aq)


OH( aq)
NaOH( s) 
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+

Na(aq)


OH( aq)
Free ions
So the free ions that are produced by the dissociation of a base in aqueous solution…
NaOH( s) 
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+
Na+
OH–
Na+
OH–
OH–
Na+
OH–
Na+

Na(aq)


OH( aq)
Already
ions
were already ions in the solid NaOH. So we can’t really call this process ionization. The ions are
simply breaking apart from one another so we call it dissociation.
Where do we find
strong bases?
Now that we know what strong bases are, where do we find them.
Any ion or compound that
produces a high
concentration of hydroxide
(OH–) ions is a strong base.
In general, any ion or compound that when added to water, produces a high concentration of
hydroxide or OH minus ions, is a strong base.
The oxide ion
(O2–) and the
amide ion
(NH2–) are
Strong Bases
Looking at the bottom of the acid table, the two ions right below hydroxide on the right side of the
table are classified as strong bases. These are the oxide ion (O 2minus) and the amide ion (NH2 minus)
Both of these
have single
arrows pointing
to the left
Notice that both of these reactions on the table have single arrows pointing to the left. This
means the ions O2 minus and NH2 minus react 100% with water.
2


O(aq)
 H 2O( l )  OH(aq)
 OH(aq)
We’ll look at the reaction of the oxide ion
2


O(aq)
 H 2O( l )  OH(a

OH
q)
(aq)
A Strong
Brønsted-Lowry
base
Because O2minus is a strong Bronsted-Lowry base.
H+
2


O(a

H
O

OH

OH
q)
2 (l)
(aq)
(aq )
A Strong
Brønsted-Lowry
base
It means it will accept a proton, or H+ ion from water.
H+


O(2aq)
 H 2O( l )  OH(aq )  OH(a
q)
When an O 2- ion gains a proton, it forms a hydroxide or OH minus ion.
H+


O(2aq)
 H 2O( l )  OH(aq )  OH(a
q)
And when a water loses a proton, it also forms a hydroxide ion.
H+
2


O(aq)
 H 2O( l )  OH(aq)
 OH(a
q)
So this reaction produces 2 hydroxide ions.
2

O(aq)
 H 2O( l )  2OH(aq)
And can be re-written as O 2minus plus water gives 2 OH minus ions.
2

O(aq)
 H 2O( l )  2OH(aq)
The single arrow pointing to the right here indicates that this reaction
2

O(aq)
 H 2O( l )  2OH(aq)
Goes to
Completion
Goes to completion. Every single O 2- ion is converted to hydroxide ions.

NH 2(aq)  H 2O( l )  OH(aq)
 NH 3(aq)
When the amide ion, NH2 minus, reacts with water,
H+

NH 2(aq)  H 2O( l )  OH(aq)
 NH 3(aq)
A proton is transferred from the water to the NH2 minus ion.
H+
NH 2( aq )  H 2O( l )  OH(aq)  NH 3(aq)
When water loses a proton, it forms an OH minus, or hydroxide ion.
H+

NH 2(aq)  H 2O( l )  OH(a
q )  NH 3 ( aq)
And when NH2 minus gains a proton, it forms an ammonia molecule, NH3.
H+

NH 2(aq)  H 2O( l )  OH(aq)
 NH 3(aq)
Again, the single arrow pointing to the right here tells us that this reaction…

NH 2(aq)  H 2O( l )  OH(aq)
 NH 3(aq)
Goes to
Completion
Also goes to completion. When added to water, Every single amide ion will be converted to a
hydroxide ion and ammonia molecule.
Now we’ll look at compounds that act
as strong bases.
Now we’ll look at compounds that act as strong bases.
Now we’ll look at compounds that act
as strong bases.
Any compound that dissociates 100%
to form hydroxide (OH–) ions can be
considered a strong base.
Any compound that dissociates 100% to form hydroxide (OH–) ions can be considered a strong
base.
Let’s focus on the first two groups on the left side of the periodic table.
Alkali
Metals
Remember, all Group 1 metals are called alkali metals
Alkaline
Earth
Metals
And all Group 2 metals are called Alkaline Earth metals.
Hydroxide compounds of
Alkali Metals are ALL Strong
Bases. These include:
LiOH
NaOH
KOH
RbOH
CsOH
FrOH
Hydroxide compounds of Alkali metals are all Strong Bases.
Hydroxide compounds of
Alkali Metals are ALL Strong
Bases. These include:
LiOH
NaOH
KOH
RbOH
CsOH
FrOH
These include
Hydroxide compounds of
Alkali Metals are ALL Strong
Bases. These include:
LiOH
NaOH
KOH
RbOH
CsOH
FrOH
Lithium hydroxide
Hydroxide compounds of
Alkali Metals are ALL Strong
Bases. These include:
LiOH
NaOH
KOH
RbOH
CsOH
FrOH
Sodium hydroxide
Hydroxide compounds of
Alkali Metals are ALL Strong
Bases. These include:
LiOH
NaOH
KOH
RbOH
CsOH
FrOH
Potassium hydroxide
Hydroxide compounds of
Alkali Metals are ALL Strong
Bases. These include:
LiOH
NaOH
KOH
RbOH
CsOH
FrOH
And rubidium, cesium and francium hydroxides.
Hydroxide compounds of
Alkaline Earth Metals are
generally Strong Bases. These
include:
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
Ra(OH)2
Hydroxide compounds of Alkaline Earth Metals are generally Strong Bases.
Hydroxide compounds of
Alkaline Earth Metals are
generally Strong Bases. These
include:
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
Ra(OH)2
With the exception of beryllium hydroxide, which is known to be a covalent compound that
doesn’t release ions in solution.
Hydroxide compounds of these
Alkaline Earth Metals are
Strong Bases. These include:
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
Ra(OH)2
So we can say that hydroxide compounds of these alkaline earth metals are strong bases
Hydroxide compounds of these
Alkaline Earth Metals are
Strong Bases. They include:
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
Ra(OH)2
They include
Hydroxide compounds of these
Alkaline Earth Metals are
Strong Bases. They include:
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
Ra(OH)2
Magnesium hydroxide
Hydroxide compounds of these
Alkaline Earth Metals are
Strong Bases. They include:
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
Ra(OH)2
Calcium hydroxide
Hydroxide compounds of these
Alkaline Earth Metals are
Strong Bases. They include:
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
Ra(OH)2
Strontium hydroxide
Hydroxide compounds of these
Alkaline Earth Metals are
Strong Bases. They include:
Mg(OH)2
Ca(OH)2
Sr(OH)2
Ba(OH)2
Ra(OH)2
And barium and radium hydroxide.
Mg2+, Ca2+, Ba2+, Ra2+
But notice that according to the solubility table, magnesium, calcium, barium, and radium
hydroxides all have low solubility.
Mg2+, Ca2+, Ba2+
Strontium hydroxide is the only alkaline earth hydroxide that is identified as soluble on this
table.
Hydroxide compounds of these
Alkaline Earth Metals are
Strong Bases. They include:
Mg(OH)2 Low solubility on solubility table
Ca(OH)2 Low solubility on solubility table
Soluble on solubility table
Sr(OH)2
Ba(OH)2 Low solubility on solubility table
Ra(OH)2 Low solubility on solubility table
So even though these are all technically strong bases because the amounts that Do dissolve in
water, dissociate 100% …
Hydroxide compounds of these
Alkaline Earth Metals are
Strong Bases. They include:
Mg(OH)2 Low solubility on solubility table
Ca(OH)2 Low solubility on solubility table
Soluble on solubility table
Sr(OH)2
Ba(OH)2 Low solubility on solubility table
Ra(OH)2 Low solubility on solubility table
Strontium hydroxide is the only one that is soluble enough to produce a relatively high
concentration of hydroxide ions in solution.
Sr  OH  2(aq) 
2
Sr(aq)


2OH(aq)
The dissociation equation for strontium hydroxide is shown here.
Sr  OH  2(aq) 
2
Sr(aq)


2OH(aq)
We must be careful to use the coefficient 2 on the hydroxide when doing calculations involving
strontium hydroxide.
0.10 M
Sr  OH  2(aq ) 
2
Sr(aq)


2OH(aq )
For example, if we are given that a solution of strontium hydroxide has a concentration of 0.10
molar,
0.10 M
 2/1
1 Sr  OH  2(aq) 
2
Sr(aq)


2OH(aq)
In order to find the concentration of hydroxide ions we would have to multiply by the mole
ratio of 2 over 1
0.10 M
 2/1
1 Sr  OH  2(aq) 
2
Sr(aq)

0.20 M

2OH(aq)
So the concentration of hydroxide ions in 0.10 M strontium hydroxide is 0.20 molar.
Electrical
Conductivity of
Strong Bases
Now, we’ll have a look at the electrical conductivity of strong bases.
KOH
Let’s add enough of the strong base (click), KOH to this beaker,
KOH
To make the concentration of KOH 0.1 molar.
0.1 M
K  OH 
0.1 M
Because KOH is ionic, we know that it actually consists of a crystal lattice of K+ and OH
minus ions. We show one of each ion here.
K  OH
0.1 M
The strong base KOH will quickly and completely dissociate into free potassium and hydroxide
ions. Notice the light bulb glows to show that we now have high conductivity.
K
OH

0.1 M
Because the concentration of KOH as a whole was 0.1 molar (click), when it dissociates
the concentrations of K+ and OH minus are both 0.1 molar.
Total ion concentration
= 0.1 M + 0.1 M = 0.2 M
K
0.1 M
OH
0.1 M
So the total ion concentration in the beaker is 0.1 M plus 0.1 M
Total ion concentration
= 0.1 M + 0.1 M = 0.2 M
K
0.1 M
OH
0.1 M
Which equals 0.2 molar. This high concentration accounts for the high conductivity.
All soluble
strong bases are
Strong
Electrolytes
Because strong bases dissociate 100% into ions, all soluble strong bases will be strong
electrolytes in aqueous solution.