Acids and Bases 2

[Julius Ngwendson, instructor]
Okay, so last lecture, we ended in Section 3,

where we looked at how you
can calculate the pH of a buffer

and also to calculate the hydrogen
ion concentration from the pH.

We also looked at the relationship between
the pH and the hydrogen ion concentration,

this relationship that you have right here.

This relationship you have right here.

So i gave you guys additional notes on a table
where you had values and you saw how they changed

and by what factor the concentrations changed

and the corresponding factors
by which the pH changed, okay?

Alright, and you remember by convention,
pH values are reported to two decimals.

And we also went over all
of these exercises right here.

Now we go into strong acids, weak acids,
and strong electrolytes, okay?

So first, let us discuss this term.

Dissociation and ionization are two
terms that you are going to see often,

so let us talk about them.

Ionization and dissociation.
So what are they?

I think you guys covered this in CHEM I,

so just a quick review [of]
ionization and dissociation.

[Student] Dissociation means that they
associate in water to form lots of ions?

[Instructor] Yes, that is, they separate.

So dissociation has to do with ionic compounds.

Dissociation has to do with ionic compounds,
and it means the separation of ions in solution.

When you see the compound dissociating,
it means it separated into its ions.

So ionic compounds have cations and anions.

so together, the cation and the
anion make the ionic compound.

And then ionization will have to do
with molecular compounds.

This class of molecular compounds
do NOT have ions,

but they form ions once
they dissolve in water.

So the formation of ions in solution;
once they dissolve in water, they form ions.

So there is a difference between
dissociation and ionization.

Ionization has to go with organic com—
[corrects self] molecular compounds

and dissociation has to do with ionic compounds.

So strong electrolytes means there is
100% dissociation or ionization,

depending on what you are talking about.

Strong electrolytes.

And examples of strong electrolytes...

examples of strong electrolytes are
strong acids, strong bases, and salts.

For now, I will just leave it as "salts."

Later on in the chapter, we are
going to talk about insoluble salts.

For now, I would just leave it as "salts."

All the salts that we are going to
cover here now are soluble salts,

but we'll make that difference later on.

So strong electrolytes, okay.

Strong electrolytes: strong acids,
strong bases, and salts.

And what do strong electrolytes do?
They dissociate or they ionize completely, 100%.

So it will be good that you are
familiar with this terminology

because this is what we are going to apply;

a lot, all of this right here,
we are going to apply these a lot.

So having described all of that, so strong
electrolytes, 100% dissociation or ionization.

Now this is a salt. We said we have
three classes of strong electrolytes:

strong acids, strong bases, and salts.

So this is a salt.

And this arrow means complete ionization.
That is, everything goes to the right.

Everything goes to the right, so if you
look at a solution of sodium chloride,

you will not find any sodium
chloride compound in it.

If you examine the solution of
a sodium chloride compound,

sodium chloride dissolves in water.

You will not find any sodium chloride in it.

Everything is going to be
in the form of these ions.

Complete dissociation. [repeats]

Now let's go to the acids and bases
handout, which I gave you guys.

So i suggested to you guys that you
should study it as soon as you can.

You'll want to study this as soon as you can.

Alright, so let's go to the first page.

I used to give this as an assignment

for students to write it out as their
first assignment in this chapter.

I realize that some students will
have difficulty coming up with this list,

so now I have done the work for you guys.

Now you have to study them
so you get to know them.

Alright, so this first table has the strong acids,
and you have their names right here.

You have to know these names
and this chemical formula

for each of these strong acids.

And we say they undergo complete ionization.
Look at what that word means.

This is the word here: complete.
It goes to the right, okay?

If you look at a solution,

if you examine a solution
of hydrochloric acid,

you will not find hydrochloric
acid molecules in it, no.

You will not find it in one.

It has ionized completely into—

It has broken down completely into its ions.

You can write this equation in two ways:

In the second option, you can
include a molecule of water.

If you include a molecule of water,

then the proton will [bond] to that molecule
of water to give you the hydronium ion.

So you have two options.

Usually, I just go with the first option
because it's easier, but take note

that you have two options.

Experimentally, this is what actually happens.

The proton gets bound to a water molecule
to give you the hydronium ion, experimentally.

But both options are used interchangeably,

so no matter which one is used,
you know what it is talking about.

Alright, so all acids release the proton,
as we discussed yesterday.

All acids release the proton,

so they ionize to generate the proton.

And anther thing you would
observe with strong acids

is that they have spectator ions.

So the conjugate base is a spectator ion
as you observe in this last column right here.

TIME 0:10:00

The only strong acid that does not
have a spectator ion is sulfuric acid.

because the conjugate base is a WEAK acid.

[Student]
Wait, the spectator ion is the base only?

[Instructor] The spectator
ion is a conjugate base.

[Student] Oh, okay.
[Instructor] Mm-hmm.

The only strong acid that does NOT
have a spectator ion is sulfuric acid.

Take note of that because the
conjugate base is a WEAK acid,

as we are going to see
in one of the tables below.

So when you are writing the equation,
the complete ionization of sulfuric acid,

the first process, the first process is STRING.

Okay? The release of the first proton
is what makes sulfuric acid a STRONG acid.

But the release of the second proton
is NOT a strong process,

so we are going to see what
weak acids do at the bottom.

[Student] So the spectator ions
are always negatively charged?

[Instructor] Well, you need to
have charge neutrality, right?

[Student] Yeah.

[Instructor] So if you break off this proton,

then the conjugate base
has to be negatively charged

in order for you to have charge neutrality.

[Student] Okay.

[Instructor] Alright, so this is
a list of your strong acids, guys.

Study them very well.

You need to be able to recognize
your strong acids and your weak acids

because if you are given a solution
to calculate the pH,

the very first question you
have to ask yourself [is]:

Am I dealing with a STRONG acid
or am I dealing with a WEAK acid?

You approach them differently,

so if you have not started studying this,
make sure you study it, okay?

Because if you treat a
strong acid as a weak acid,

you are not going to get the right answer.

If you treat a weak acid as a strong acid,
you will not get the right answer.

So schedule yourself to
study these 11 strong acids.

Some tables will list chloric acid as a weak acid
because it's somewhere on the borderline.

You don't worry about that.
Here, we treat it as a STRONG acid, okay?

Alright, so these questions are
just to help you think a little bit,

and in this thinking, you are going to
enable the information from that table

(that first table) to stick on your minds.

Now we go to weak acids. We go to weak acids.

Now, what is the difference between
a strong acid and a weak acid?

There is PARTIAL ionization.
The ionization is NOT complete.

Okay? Partial ionization.
It goes back and forth.

You see it establishes an equilibrium.
A lot of what we did in the previous chapter.

It establishes an equilibrium.

So you take note of the difference in equation
already between a STRONG acid and a WEAK acid.

[For] a strong acid, you have [a]
one-sided arrow, forward arrow.

Weak acid goes back and forth.
A weak acid goes back and forth.

It establishes an equilibrium.

Now, quantitatively, if you look—

If you examine the solution of this weak
acid right here (this hydrofluoric acid),

if you examine its solution, okay?

Now depending on the concentration,

but averagely, if you examine
a solution of hydrofluoric acid,

listen carefully, guys: 95% of it
will still be the molecule intact.

95% of it will still be the molecule intact.
Only about 5% of it will ionize.

So not only do weak acids
establish an equilibrium,

but only a small amount of weak acids ionize.

Take note of those two things.

TIME 0:15:00

So weak acids ionize partially
and only to a small extent.

So we have a list of weak acids here:
hydrocyanic acid—

also, like strong acids, you can write them with
or without a water molecule; it doesn't matter.

Nitrous acid is a weak acid as well.

Formic acid—So these two
are actually organic acids.

Formic acid, this is your acidic hydrogen,

the hydrogen that breaks off;
as you can observe there, it breaks off.

Acetic acid, what you have in vinegar,
breaks off that acidic hydrogen.

That's what breaks off, okay?

Then hypochlorous acid is a weak acid.
Chlorous acid is a weak acid as well.

Hydrosulfuric acid—

Now, hydrosulfuric acid is also diprotic.
In other words, it has two protons.

You see the release of the first proton
right here, the release of the first proton.

And then the conjugate base
is also a weak acid on its own

and it undergoes another ionization right here.

So take note of that.

Hydrogen sulfate— Now this is a
conjugate base of sulfuric acid,

which we discussed in the previous table.

You observe that it is a weak process.

When sulfuric acid dissolves in water,
it undergoes two steps of ionization.

The first is a STRONG process,
the second is a WEAK process.

TIME 17:20

Let us just summarize that right here.

So when you dissolve sulfuric acid in water,
H2SO4, sulfuric acid in water,

it has two protons; it is diprotic.

The first ionization is a strong process,

one-sided arrow, complete ionization to give you
the hydrogen ion and the hydrogen sulfate ion.

This is what you guys did
in your first dry lab activity.

Question 2 on the second page to show how
strong electrolytes dissociate in solution.

Most of you broke off the second hydrogen.
It doesn't break off in a strong process.

So the conjugate base is a weak acid.

It ionizes by a WEAK process,
that is, establishes an equilibrium.

So we have two-sided arrows right there

to release the second proton
plus the sulfate polyatomic ion.

So the first is a STRONG
process that is complete;

and the second is a WEAK process.

It is only one acid that does this,

where it has a combination of a strong process
and a weak process in its ionization.

Only one acid: sulfuric acid.

Okay, so we go back to the table for weak acids,
so this is your hydrogen sulfate right here.

TIME 0:20:00

The ammonium ion, it is a conjugate acid
of ammonia. It is also, itself, a weak acid.

The ammonium ion. Take note right there.

It releases the hydrogen ion by a WEAK process.

Sulfurous acid is also diprotic.

Sulfurous acid is also diprotic so it
undergoes two steps in its ionization

and they are all weak processes.

They are all weak processes.

Phosphoric acid is the highest, it's triprotic.

It undergoes ionization through three
processes and they are all WEAK.

Carbonic acid. How can you make a solution
of carbonic acid at home? Who knows?

How can you make a solution
of carbonic acid at home?

Anybody knows that?

You just take a cup of water and a straw,
put the straw into the cup of water,

and you keep exhaling, keep exhaling.

Your exhaled air has high
concentrations of carbon dioxide.

As you exhale it through the straw
into the water, it mixes--

carbon dioxide mixes with water
to give you carbonic acid.

H2O plus CO2 gives you H2CO3.

You keep exhaling for, like, 5 minutes,

you will have a concentrated
solution of carbonic acid.

Okay? It's a weak acid.

[Student] Does it change the look of it?

[Instructor] No, it's colorless, but if you
have a pH paper, you would see it changing.

An acid changes the pH paper
from what color to what color?

[Student] Change blue to red.

[Instructor] Change blue litmus paper to red.

So as you keep exhaling and exhale and exhale,

and you test it with your litmus paper,

you will see the litmus paper
getting more and more red.

[Student] Okay.
[Instructor] Mm-hmm.

Just that you cannot tell it by observation

because it is a colorless acid.

So it is diprotic,
also ionizes through two steps.

So know the difference between
a strong acid and a weak acid

and what they are and the
differences in their equations,

in writing their equations.

So like strong acids, like strong ACIDS,
we also have strong BASES.

You know the difference,
that strong bases dissociate.

Strong ACIDS ionize.
That's their difference.

Their similarity is,
both processes are complete.

Strong bases, you see one-sided arrow;
everything separates.

Now with strong bases
that have two hydroxide ions,

when you are solving problems,
take note of this stoichiometry.

You take note of the stoichiometry

because both hydroxides are released at once.

You take note of this stoichiometry.

when you are solving problems with
strong bases that have two hydroxide ions.

TIME 24:10

And like strong acids,
they, too, have spectator ions.

You can see their spectator ions
in the last column, the fourth column.

So please, I would encourage you guys,

if you have not studied this table,
then you are beginning to fall behind.

Study this table and practice
writing out these equations

and know the substances
in each of these tables.

Finally, weak bases.

Like weak acids, they have two-sided arrows.
They establish an equilibrium, okay?

For weak bases, you always
have to use water in your equation

because that is where they
get their hydrogen ions from.

Yesterday, in the last lecture,
we discussed about Bronsted bases, proton acceptors.

So when a weak base is dissolved in water,
it accepts a proton from water.

That is why, in its equation,
you need to show a molecule of water.

In its equation, you need to show
a molecule of water right there.

So ammonia here, you see it
accepts a proton from water

to give the conjugate acid,
now the ammonium ion,

and what results from water
is the hydroxide ion, okay?

TIME 26:00

Now methyl amine behaves just like ammonia.

You can see a portion of ammonia right there

where one of the hydrogen atoms
has been [sounds cuts out].

You guys will see a lot of this
in organic chemistry, but it behaves the same way.

You see, when it accepts a proton,
it looks like ammonia.

So if you can write the equation for ammonia,

you can also write that for
methyl amine, pyridine, aniline.

They all behave just like ammonia.
Even urea as well as hydrazine.

Caffeine, [sound cuts out]
okay, the same thing,

accepts a hydrogen ion from water
to give you the conjugate [sound cuts out].

TIME 27:05

Now the fluoride ion, this has some
peculiar cases that you guys need to study.

The fluoride ion is a WEAK base, okay?

In solution, the fluoride ion picks up a proton
from water to generate the weak acid.

Again, to a very small extent.

So let's put a few things together here.
Let's put a few things together.

We just discussed the fluoride ion, okay?
Now look at the weak acid hydrofluoric acid.

When hydrofluoric acid is dissolved in water,
it's a weak acid. It establishes an equilibrium.

[Unclear] a conjugate base,
the fluoride ion. Okay?

Take note, this reversed arrow right here,

it shows that the fluoride ion combines
with the hydrogen ion (right?) to go backward.

It shows that the fluoride ion combines
with the hydrogen ion in the reverse reaction.

So if you have sodium fluoride,
now this is a salt.

These are things you'll be dealing with.

If you have sodium fluoride, this is a salt,
and we said salts are strong electrolytes.

Complete dissociation.
This is what you will have right here.

Complete dissociation to release
the sodium ion and the fluoride ion.

Now we have listed the sodium ion
as a spectator ion in the first table.

When you go to watch a match as a spectator,
you really don't participate in that match, right?

You just sit on the side and watch.

So this is a spectator ion; it does not
participate in the chemistry of this solution.

So know your spectator ions.

If you don't know your spectator ions,

you will be forcing them to react
when they do not react, okay?

But the fluoride ion is a weak base.
Look at here. It combines with the hydrogen ion.

So when you dissolve sodium fluoride in water,
Step 1, it is going to dissociate completely.

And then Step 2, the weak base.

The weak base is going to react with water
(a molecule of water) because it is a weak base.

This happens with ALL weak bases. Don't forget.

Because it is weak, you have a double-sided arrow

and it picks up a proton from water
to generate hydrofluoric acid.

Again, to a very small extent--

[Student] I have a quick question.
[Instructor] Just a second.

Plus the hydroxide ion, which is the
leftover from water, okay? Right there.

So when you dissolve salt
in water, okay, and if-- When--

If you dissolve a salt in water
that has a weak base, okay,

you will always have these two steps.

Take note. You will always have these two steps.

So this is a WEAK base,
and that is what weak bases do.

Okay, somebody has a question. Sandra?

[Sandra] So because of the arrow-- Would you--

Would it always be a weak base then,
when you have the arrows?

Is that how you would know it's weaker?

[Instructor] Yes.
[Sandra] If that makes sense.

[Instructor] Yup, yup.
[Other student, unclear]

[Instructor] So weak bases, right?
{Sandra] Mm-hmm.

[Instructor] Weak bases,
you observe what we write there.

The double-sided arrow means they are weak.

So that's why we need to study all of these
so that each time you are dealing with them,

you know what you are dealing with.

As well as weak acids. You see?
Double-sided arrow.

That's why we need to study all of these
so that when you are dealing with them,

you know what you are dealing with right there.

Okay, so that was the reason why
we were explaining this fluoride ion.

You can have the fluoride ion in water
if you dissolve a salt like sodium fluoride.

It dissociates, okay,
and the fluoride ion becomes free.

And when the fluoride ion is free in water,
that is what it will do in water, okay?

The same thing with the nitrite ion, okay?
It's a weak base.

And the hypochlorite ion, and so on and so forth.

The acetate ion, the conjugate base
of sulfuric acid, it is a weak base also.

So guys, study these things,
be able to write these equations.

It would serve you both in this chapter
and in the next chapter, Chapter 16.

Your two biggest chapters in this course.

If you are able to write these equations,

Chapter 16 will be easier for you because
you know what you are dealing with,

you know the equations.

Feel free, if you have any questions, ask.

Okay, so we have covered all of this right here.

We have covered strong acids,
we've also covered salts

and weak acids are weak electrolytes,
not completely dissociated, okay?

These are examples of weak acids
and then strong bases.

Again, when you are writing
equations for strong bases,

don't forget your stoichiometry.

And weak bases, as well,
establish an equilibrium.

The conjugate base of a strong acid
has no measurable strength.

That is, the conjugate base
of a strong acid is very weak.

That's another way to put it.
That is why it is a spectator ion.

So this is a strong acid, okay?

Complete ionization to give you
the hydrogen ion plus a conjugate base.

So we said the conjugate base of a strong acid
has no measurable strength.

This is the conjugate base right here
from the last lecture that we studied.

This just means this conjugate base
is VERY, VERY weak, okay? Very weak.

That is why it is a spectator ion.
It does not do anything.

It does not have the strength
to recombine with the proton,

so it's a spectator ion.

That's what this sentence is talking about.

Okay?

The hydronium ion is the strongest acid
that can exist in aqueous solution,

so you measure the strength--
the acid strength of a solution

by measuring its amount of hydronium ion, okay?

The concentration of hydronium ions
determines how acidic a solution is.

That's another way of explaining
this sentence right here.

And the hydroxide ion is the strongest base
that can exist in aqueous solution,

so the concentration of the hydroxide ions
determine how basic your solution is, okay?

TIME 38:00

So this gives a good picture of a strong acid.

This is before ionization.

Before ionization, the molecule is intact.

After ionization, you see that
the molecule is completely ionized.

Completely. There is no molecule in it.
Everything has been converted into its ions.

So when you look into the solution,

you find the chloride ions
that are all separated.

Find the chloride ions,
that they're all separated,

And you also find the hydronium ions,
which are the protons combined with molecules.

So you see the molecule is completely ionized.

You see complete ionization right there.
That's what happens with a strong acid.

The cation and anion are completely separated.

For a weak acid, before ionization--

Before ionization,
you see the molecule is intact.

At equilibrium, you see about
95% of the molecule is still intact.

About 95% is still intact.

Only a SMALL amount has formed ions, okay?
Only a small amount has formed ions.

So you can see the molecules
still intact right there.

That's your molecules still intact...

your molecules still intact...

your molecules still intact...

molecule intact...

molecule intact, okay?

But you have-- In this case, in this picture,
you have just one molecule that has ionized.

Just one molecule that has ionized to give you
the chloride ion and the hydronium ion.

Only one molecule that ionized, okay?

You have the other five.
They are still intact.

So there are some national-level exams
that you guys might take,

maybe like PCAT or MCAT or your exam
into the Dental School, and so on.

Sometimes, they will show you pictures like this.

They will show you, like, four pictures:

strong acid, weak acid,
high concentration, low concentration,

and they ask you to identify, okay?

So these are the concepts
that should come to your mind

when you are looking at
those kinds of questions.

Okay, so some strong acids and some weak acids,

okay, we've already covered
as well as their conjugate bases.

So for STRONG acids, their conjugate bases
are spectator ions EXCEPT hydrogen sulfate,

EXCEPT the hydrogen sulfate,
which we have discussed.

Weak acids-- Sometimes students used to get
confused: Is ammonia a weak BASE or a weak ACID?

Ammonia is both, but ammonia
will only act as a weak acid

in the presence of a VERY strong base.

Those kinds of bases are
out of the scope of this study.

So if this is a little bit confusing to you
that ammonia is a weak acid,

you can just ignore it.

If that is confusing to you,
then you can ignore that.

But, of course, you need to know
that ammonia is a WEAK base

because you will deal with it
a number of times in this course.

Alright, so now we have settled the matter

between strong acids, weak acids,
strong bases, and weak bases.

Now we need to start applying
those concepts into calculations.

So if you are given a solution
to calculate the pH of that solution,

you need to ask yourself:

Am I dealing with a strong acid or a weak acid?
Am I dealing with a strong base or a weak base?

Depending on which class, that is how
you are going to approach the question.

Alright, example: Calculate the pH of 1.0 times
10 to the minus 3 molar hydrochloric acid.

Calculate the pH of 1.0 times
10 to the minus 3 molar hydrochloric acid.

So what kind of acid is hydrochloric acid?

What kind of acid is hydrochloric acid?

[Camille] Strong.

[Instructor] Camille was very smart
to see it right here, right? [chuckles]

It was right there in front of you guys.
[chuckling] Right there.

[Student] I didn't realize I was on mute.
[Instructor] I see.

So it's a strong acid. That means this is
how you have to write its equation.

And you need to know the meaning of that arrow.

That arrow carries a meaning;
it means everything goes to the right

So initially, your question gives you

1.0 times 10 to the power
minus 3 molar hydrochloric acid.

There is zero amount of hydrogen ions,
zero amount of chloride ions.

[Student] At that one there,

the arrow goes to the right
and means complete ionization.

[Instructor] Yes, that is what
will happen in the final step.

We are still initially, before ionization.

[Student] Okay.
[Instructor] Yup.

Then you apply the meaning of
that arrow now to the CHANGE.

Okay, Audrey, this is where you apply
the meaning of that arrow to the change.

Because it's a strong acid, complete ionization,

so your change will be the same amount
as your initial amount, just negative.

Because it is a strong acid, everything ionizes.

And you have stoichiometric amounts
for your products as well, okay?

And then you get the final,
which is the sum of initial and change.

TIME 0:47:00