A salt is an ionic compound consisting of a cation other than H+ and an anion other
than OH minus. Here, we’ll show you all about hydrolysis of ions in salts.
Acidic
Salts
Neutral
Basic
A salt can either be acidic (click) neutral, or (click) basic depending the on the
hydrolysis of it ions.
We’re sometimes given the formula for a salt and asked to determine whether it is
acidic, basic, or neutral when dissolved in water.
Process for Determining Whether a
Salt is Acidic, Basic, or Neutral
1. Write a dissociation equation for the salt to find
its cation and anion.
2. Eliminate any spectator ions.
3. Locate the remaining ions on the acid table and
decide whether they undergo acid or base
hydrolysis.
4. If both ions undergo hydrolysis, use Ka and Kb
values to determine which hydrolysis is
predominant.
There is a step by step process we can use to determine whether a given salt is
acidic, basic or neutral in aqueous solution.
Process for Determining Whether a
Salt is Acidic, Basic, or Neutral
1. Write a dissociation equation for the salt to find
its cation and anion.
2. Eliminate any spectator ions.
3. Locate the remaining ions on the acid table and
decide whether they undergo acid or base
hydrolysis.
4. If both ions undergo hydrolysis, use Ka and Kb
values to determine which hydrolysis is
predominant.
Step 1 is to write a dissociation equation for the salt in order to determine what its
cation and anion are.
Process for Determining Whether a
Salt is Acidic, Basic, or Neutral
1. Write a dissociation equation for the salt to find
its cation and anion.
2. Eliminate any spectator ions.
3. Locate the remaining ions on the acid table and
decide whether they undergo acid or base
hydrolysis.
4. If both ions undergo hydrolysis, use Ka and Kb
values to determine which hydrolysis is
predominant.
Step 2 is to eliminate any spectator ions.
1
2
The Spectator Cations
Remember, spectator cations are the positive ions of Group 1, or alkali metals, and
Group 2, or alkaline earth metals.
1
2
The Spectator Cations
Always Neutral in
Aqueous Solution
So these ions are always neutral in aqueous solution.
The Spectator
Anions
The spectator anions are the top 5 ions on the right side of the acid table. They are
perchlorate, iodide, bromide, chloride, and nitrate.
The Spectator
Anions
They do NOT
react with water
and are always
NEUTRAL in
aqueous solutions
These ions do not react with water and are always neutral in aqueous solution.
1
2
Spectator
Cations
Spectator
Anions
It’s good to
memorize these!
The Spectator Ions
We can list all the spectator cations and spectator anions in a single box and use
this whenever we have to determine whether a salt is acidic, basic, or neutral.
1
2
Spectator
Cations
Spectator
Anions
It’s good to
memorize these!
The Spectator Ions
It is a good idea to memorize these in order to save time later. At this point you
may want to pause the video, take a screen shot of this and print it.
Process for Determining Whether a
Salt is Acidic, Basic, or Neutral
1. Write a dissociation equation for the salt to find
its cation and anion.
2. Eliminate any spectator ions.
3. Locate the remaining ions on the acid table and
decide whether they undergo acid or base
hydrolysis.
4. If both ions undergo hydrolysis, use Ka and Kb
values to determine which hydrolysis is
predominant.
Once we have eliminated the spectator ions, the third step is to locate the remaining ion or ions on the acid
table. If an ion is not a spectator ion, that means it must undergo either acid or base hydrolysis, or both.
or Fe3+
or Cr3+
or Al3+
Cations that Hydrolyze
In Chemistry 12, these are the four cations that hydrolyze. They all undergo acid
hydrolysis.
or Fe3+
or Cr3+
or Al3+
Cations that Hydrolyze
Notice the three hydrated cations, iron(III), chromium(III), and aluminum can be depicted either
in their hydrated (or hexaaquo) form,
or Fe3+
or Cr3+
or Al3+
Cations that Hydrolyze
or in the form of simple ions with a 3+ charge.
or Fe3+
or Cr3+
or Al3+
or NH4+
Cations that Hydrolyze
When you dissociate a salt, you’re likely to see these cations depicted in this
simple form.
or Fe3+
or Cr3+
or Al3+
or NH4+
Cations that Hydrolyze
Just keep in mind that if you need to write a hydrolysis equation for one of these
three, you must (click) convert them to their hydrated form
or Fe3+
or Cr3+
or Al3+
Cations that Hydrolyze
The other hydrolyzing cation, ammonium, always appears as NH4 plus or in
compound formulas as NH4.
Anions that
Undergo ONLY
Base Hydrolysis
Now for anions. Anions are on the right side of the acid table. We’ll start by looking
at anions that undergo ONLY base hydrolysis.
Anions that
Undergo ONLY
Base Hydrolysis
That’s these ions here.
Anions that
Undergo ONLY
Base Hydrolysis
Excluding the spectator ions on the top right of the table, these are all the ions on
the right with a negative charge, whose formulas do NOT start with “H”.
Amphiprotic
Anions
Undergo BOTH
Acid and Base
Hydrolysis
Amphiprotic anions are the negative ions on the right side, whose formulas start
with an “H”
Amphiprotic
Anions
Undergo BOTH
Acid and Base
Hydrolysis
Amphiprotic anions undergo BOTH acid and base hydrolysis. What we have to do with these is determine which
hydrolysis is predominant. How to do that is shown on the video “Hydrolysis of Amphiprotic Anions”
Amphiprotic
Anions
Undergo BOTH
Acid and Base
Hydrolysis
Here are the amphiprotic anions. Notice their formulas all start with “H” and they
all have negative charges.
Process for Determining Whether a
Salt is Acidic, Basic, or Neutral
1. Write a dissociation equation for the salt to find
its cation and anion.
2. Eliminate any spectator ions.
3. Locate the remaining ions on the acid table and
decide whether they undergo acid or base
hydrolysis.
4. If both ions undergo hydrolysis, use Ka and Kb
values to determine which hydrolysis is
predominant.
The fourth step of our process comes into play in cases where both the cation and
anion of the salt hydrolyze.
Process for Determining Whether a
Salt is Acidic, Basic, or Neutral
1. Write a dissociation equation for the salt to find
its cation and anion.
2. Eliminate any spectator ions.
3. Locate the remaining ions on the acid table and
decide whether they undergo acid or base
hydrolysis.
4. If both ions undergo hydrolysis, use Ka and Kb
values to determine which hydrolysis is
predominant.
If both cation and anion hydrolyze, we compare the value of the Ka for the cation to the value of Kb for the
anion in order to decide which hydrolysis is predominant. We’ll go through an example of this later.
Now we’ll go through a few examples working with salts.
Is the salt calcium nitrite, Ca(NO2)2,
acidic, basic, or neutral?
We’re asked to determine whether the salt calcium nitrite, with the formula
Ca NO2 two, is acidic, basic, or neutral when dissolved in water.
Process for Determining Whether a
Salt is Acidic, Basic, or Neutral
1. Write a dissociation equation for the salt to find
its cation and anion.
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
The first step in our process is to write the dissociation equation for the salt.
1. Write a dissociation equation for the salt to find
its cation and anion.
Ca  NO 2  2(aq ) 
2
Ca(aq)


2NO 2(aq )
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
We start with the formula Ca (NO2) 2.
1. Write a dissociation equation for the salt to find
its cation and anion.
Ca  NO 2  2(aq) 
2
Ca(aq)


2NO2(aq)
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
It dissociates into a calcium ion, Ca 2 plus,
1. Write a dissociation equation for the salt to find
its cation and anion.
Ca  NO 2  2(aq) 
2
Ca(aq)


2NO2(aq)
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
And two nitrite, or NO2 minus ions.
2. Eliminate any spectator ions.
Ca  NO 2  2(aq) 
2
Ca(aq)


2NO 2(aq)
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
The second step in the process is to eliminate any spectator ions.
2. Eliminate any spectator ions.
Ca  NO 2  2(aq) 
2
Ca(aq)


2NO2(aq)
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
Because it’s a member of group 2, the calcium ion is a spectator ion, so it can be
(click) eliminated.
3.
Locate the remaining ions on the acid table and decide
whether they undergo acid or base hydrolysis.
Ca  NO 2  2(aq) 
2
Ca(aq)


2NO2(aq)
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
Now that we have eliminated the spectator ion, the next step is to locate the
remaining ion, nitrite, on the table.
3.
Locate the remaining ions on the acid table and decide
whether they undergo acid or base hydrolysis.
Ca  NO 2  2(aq ) 
2
Ca(aq)


2NO2(aq )
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
The nitrite ion is on the right side of the acid table, in the weak base section. It does not
start with an “H”, so it is not amphiprotic. It undergoes only base hydrolysis.
3.
Locate the remaining ions on the acid table and decide
whether they undergo acid or base hydrolysis.
Ca  NO 2  2(aq ) 
2
Ca(aq)


2NO2(aq )
basic
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
Therefore, we can say that NO2 minus is basic. (pause)
3.
Locate the remaining ions on the acid table and decide
whether they undergo acid or base hydrolysis.
Ca  NO 2  2(aq ) 
2
Ca(aq)
A neutral
spectator


2NO2(aq )
basic
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
Because Ca2+ is a neutral spectator and (click) NO2 minus is basic
3.
Locate the remaining ions on the acid table and decide
whether they undergo acid or base hydrolysis.
Ca  NO 2  2(aq ) 
2
Ca(aq)
A neutral
spectator


2NO2(aq )
basic
The salt Ca(NO2)2
is BASIC
Is the salt calcium nitrite, Ca(NO2)2, acidic, basic,
or neutral?
We can say that the salt Ca(NO2)2, or calcium nitrite, is basic. So we’ve now
answered this question.
Is the salt potassium iodide, KI,
acidic, basic, or neutral?
We’re asked to determine whether the salt potassium iodide, with the formula
KI, is acidic, basic, or neutral when dissolved in water.
KI( aq) 

K (aq)


I( aq )
Is the salt potassium iodide, KI, acidic, basic,
or neutral?
We start by writing the dissociation equation for KI
KI( aq) 

K (aq)


I( aq )
Is the salt potassium iodide, KI, acidic, basic,
or neutral?
Its KI gives K+ plus I minus. Now we eliminate spectator ions
KI(aq) 

K (aq)


I(aq)
Is the salt potassium iodide, KI, acidic, basic,
or neutral?
K+ is in group 1, (click) so it is a neutral spectator which can be eliminated.
KI( aq) 

K (aq)


I( aq )
Is the salt potassium iodide, KI, acidic, basic,
or neutral?
And I minus is one of the top 5 ions on the right side of the acid table, (click) so it
is also a neutral spectator, which can be eliminated.
KI( aq) 

K (aq)

A neutral
spectator

I( aq )
A neutral
spectator
Is the salt potassium iodide, KI, acidic, basic,
or neutral?
So both the cation and the anion of this salt are neutral spectator ions,
KI( aq) 

K (aq)

A neutral
spectator

I( aq )
A neutral
spectator
The salt KI is
NEUTRAL
Is the salt potassium iodide, KI, acidic, basic,
or neutral?
Therefore the salt, KI, is neutral.
Is the salt chromium(III) nitrate,
Cr(NO3)3, acidic, basic, or neutral?
Here’s another example. We’re asked to determine whether the salt chromium(III) nitrate,
with the formula Cr(NO3)3, is acidic, basic, or neutral when dissolved in water.
3

Cr  NO 3  3(aq)  Cr(aq)
 3NO 3(aq)
Is the salt chromium(III) nitrate, Cr(NO3)3, acidic,
basic, or neutral?
We’ll start by writing the dissociation equation for Cr(NO3)3
3

Cr  NO 3  3(aq )  Cr(aq)
 3NO3(aq
)
Is the salt chromium(III) nitrate, Cr(NO3)3, acidic,
basic, or neutral?
We get the cation Cr 3+ or chromium(III) and (click) the anion NO3 minus, nitrate.
3

Cr  NO 3  3(aq)  Cr(aq)
 3NO3(aq)
Is the salt chromium(III) nitrate, Cr(NO3)3, acidic,
basic, or neutral?
Cr 3+ is not in group 1 or 2 on the periodic table, so it is not a spectator cation
3
Cr  NO 3  3(aq)  Cr(aq)
 3NO3(aq)
Is the salt chromium(III) nitrate, Cr(NO3)3, acidic,
basic, or neutral?
But the anion NO3 minus is one of the top 5 neutral spectator ions on the right side
of the table, (click) so it can be eliminated.
3

Cr  NO 3  3(aq )  Cr(aq)
 3NO3(aq
)
Is the salt chromium(III) nitrate, Cr(NO3)3, acidic,
basic, or neutral?
Going back to Cr 3+,
3

Cr  NO 3  3(aq )  Cr(aq)
 3NO3(aq
)
Is the salt chromium(III) nitrate, Cr(NO3)3, acidic,
basic, or neutral?
Cr 3+, or chromium(III), is one of the acidic cations.
3

Cr  NO 3  3(aq )  Cr(aq)
 3NO3(aq
)
acidic
Is the salt chromium(III) nitrate, Cr(NO3)3, acidic,
basic, or neutral?
So we can say that Cr 3+ is acidic.
3

Cr  NO 3  3(aq )  Cr(aq)
 3NO3(aq
)
acidic
A neutral
spectator
Is the salt chromium(III) nitrate, Cr(NO3)3, acidic,
basic, or neutral?
Because Cr 3+ is acidic, (click) and NO3 minus is a neutral spectator,
3

Cr  NO 3  3(aq )  Cr(aq)
 3NO3(aq
)
acidic
A neutral
spectator
The salt Cr(NO3)3
is ACIDIC
Is the salt chromium(III) nitrate, Cr(NO3)3, acidic,
basic, or neutral?
We can say the salt Cr(NO3)3 is acidic
Is the salt ammonium oxalate,
(NH4)2C2O4, acidic, basic, or neutral?
Here’s one more example. We’re asked to determine whether the salt ammonium oxalate,
with the formula (NH4)2C2O4, is acidic, basic, or neutral when dissolved in water.
 NH4  2 C2O4(aq) 

2NH4(aq)

2
C2O4(aq)
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
We start by writing the dissociation equation for (NH4)2C2O4.
 NH4  2 C2O4(aq) 

2NH4(aq)

2
C2O4(aq)
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
So we have the cation NH4+, and (click) the anion C2O4 2 minus
 NH4  2 C2O4(aq) 

2NH4( aq )

2
C2O4 (aq)
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
The cation NH4+, is one of the 4 acidic cations on the left side of the acid table.
 NH4  2 C2O4(aq) 

2NH4( aq )

2
C2O4 (aq)
acidic
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
So we can say that NH4 + is acidic.
 NH4  2 C2O4(aq) 

2NH4(aq)

2
C2O4(aq )
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
The anion C2O4 2 minus is found on the right side of the acid table, in the weak
base section.
 NH4  2 C2O4(aq) 

2NH4(aq)
acidic

2
C2O4(aq )
basic
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
So we can say that C2O4 2 minus is basic.
 NH4  2 C2O4(aq) 

2NH4(aq)
acidic

2
C2O4(aq)
basic
Neither of these
are spectator ions
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
We see that neither the cation nor the anion of this salt are spectators. They both
hydrolyze.
Process for Determining Whether a
Salt is Acidic, Basic, or Neutral
1. Write a dissociation equation for the salt to find
its cation and anion.
2. Eliminate any spectator ions.
3. Locate the remaining ions on the acid table and
decide whether they undergo acid or base
hydrolysis.
4. If both ions undergo hydrolysis, use Ka and Kb
values to determine which hydrolysis is
predominant.
Remember, if both cation and anion hydrolyze, we compare the value of the Ka for the
cation to the value of Kb for the anion in order to decide which hydrolysis is predominant.
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )
4

2
C2O4(aq)
K b (C O2 )
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
So we compare the Ka of NH4 + with the Kb of C2O4 2 minus
2
4
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )  5.6  10
4
10
2
C2O4(aq )

K b (C O2 ) 
2
4
Kw
K a (HC O )
2
4
1.0  10 14

5
6.4  10
10
 1.6  10
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
Here, we’ll start by finding the value of Kb for the oxalate ion, C2O4 2 minus.
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )  5.6  10
4
10
2
C2O4(aq )

K b (C O2 ) 
2
4
Kw
K a (HC O )
2
4
1.0  10 14

5
6.4  10
10
 1.6  10
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
We locate the ion C2O4 2minus on the right side of the acid table. This is the row
we will work with to find its Kb
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )  5.6  10
4
10
2
C2O4(aq )

K b (C O2 ) 
2
4
Kw
K a (HC O )
2
4
1.0  10 14

5
6.4  10
10
 1.6  10
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
Remember the Kb of a species is Kw divided by the Ka of its conjugate acid.
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )  5.6  10
4
10
2
C2O4(aq )

K b (C O2 ) 
2
4
Kw
K a (HC O )
2
4
1.0  10 14

5
6.4  10
10
 1.6  10
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
The conjugate acid of C2O4 2 minus is HC2O4 minus
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )  5.6  10
4
10
2
C2O4(aq )

K b (C O2 ) 
2
4
Kw
K a (HC O )
2
4
1.0  10 14

5
6.4  10
10
 1.6  10
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
The value of Kw is 1 × 10–14.
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )  5.6  10
4
10
2
C2O4(aq )

K b (C O2 ) 
2
4
Kw
K a (HC O )
2
4
1.0  10 14

5
6.4  10
10
 1.6  10
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
And the value of Ka for HC2O4 minus is 6.4 × 10–5. This appears in the acid table on
the right end of the row for hydrogen oxalate, or HC2O4 minus.
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )  5.6  10
4
10
2
C2O4(aq )

K b (C O2 ) 
2
4
Kw
K a (HC O )
2
4
1.0  10 14

5
6.4  10
10
 1.6  10
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
So the value of Kb is 1 × 10–14 divided by 6.4 × 10–5,
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )  5.6  10
4
10
2
C2O4(aq )

K b (C O2 ) 
2
4
Kw
K a (HC O )
2
4
1.0  10 14

5
6.4  10
10
 1.6  10
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
Which comes out to 1.6 × 10–10.
 NH4  2 C2O4(aq) 

2NH4(aq)
K a (NH+ )  5.6  10
10
2
C2O4(aq )

K b (C O2 )  1.6  10 10
2
4
4
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
So we can summarize by saying that the value of Kb for C2O4 2 minus is
1.6 × 10–10.
 NH4  2 C2O4(aq) 

2NH4( aq )
K a (NH+ )  5.6  10 10
4
2
C2O4 (aq)

K b (C O2 )  1.6  10 10
2
4
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
Now, we’ll find the value of Ka for the cation, NH4 plus
 NH4  2 C2O4(aq) 

2NH4( aq )
K a (NH+ )  5.6  10 10
4
2
C2O4 (aq)

K b (C O2 )  1.6  10 10
2
4
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
The value of Ka for NH4 plus can be found directly on the right side of the row for
NH4 plus. (click) It is 5.6 × 10–10.
 NH4  2 C2O4(aq) 

2NH4( aq )
K a (NH+ )  5.6  10 10
4
2
C2O4 (aq)

K b (C O2 )  1.6  10 10
2
4
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
We see that Ka for the cation is 5.6 × 10–10 and (click) Kb for the anion is
1.6 × 10–10,
 NH4  2 C2O4(aq) 

2NH4( aq )
K a (NH+ )  5.6  10 10
4
2
C2O4 (aq)

K b (C O2 )  1.6  10 10
2
4
K a (cation)  K b (anion)
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
So the value of Ka for the cation is greater than the value of Kb for the anion.
 NH4  2 C2O4(aq) 

2NH4( aq )
K a (NH+ )  5.6  10 10
4
2
C2O4 (aq)

K b (C O2 )  1.6  10 10
2
4
K a (cation)  K b (anion)
The salt (NH4)2C2O4
is ACIDIC
Is the salt ammonium oxalate, (NH4)2C2O4, acidic,
basic, or neutral?
Therefore, the salt (NH4)2C2O4 is acidic. And we’ve now answered this question.
So, in summary, by knowing how ions hydrolyze,
we can find out whether any given salt is acidic, basic, or neutral when dissolved in
water