>> host: Welcome back
to Unit 7: Solutions,
Acids and Bases.
We've spent a considerable
amount of time in this unit
focusing on solutions,
but there are a couple types
of solutions that we have
not yet discussed
in great detail.
Those solution types
are acids and bases.
Acids and bases
are chemical substances
that release certain ions
when dissolved in water.
Acids and bases
are extremely
important compounds.
But before we delve into
those solutions,
we'll want to explore
a systematic approach
to naming acids.
Just like we discussed
in unit four when we talked
about how to name various ionic
and molecular compounds,
acids have their own set
of nomenclature,
or naming rules.
We can think of acids
as falling into one of
two categories: binary acids
that do not contain an oxygen
in their chemical formula,
and oxyacids,
those that do contain oxygen
in their chemical formula.
These two categories of acids
have different rules
for naming them.
When naming acids
that do not contain an oxygen
in the formula, binary acids,
we take a systematic approach.
The name of the acid
will always start with Hydro,
followed by the root of
the anion, and finally an "ic"
at the end of the name.
So some examples would be HF,
which does not have
oxygen in it,
so we name it Hydro
and then fill in the blank
with the root of the anion.
In this case, the root
of fluoride is fluor,
and then we attach
an "ic" to the ending.
So HF would be called
hydrofluoric acid,
HBr, hydrobromic acid,
HI, hydroiodic acid,
and HCN, hydrocyanic acid.
If the acid does contain
an oxygen in the formula,
in other words,
it's an oxyacid,
then the ion present
in the formula is
going to be a polyatomic ion.
So you'll need to identify
the polyatomic anion
that's found in the formula
of the acid because the name
is going to be based
on that polyatomic ion's name.
For example, H2SO4
contains oxygen in the anion.
So we need to determine
what that anion's name is.
In this case, it's sulfate.
Since an ending of -ATE
in the polyatomic
would be changed to "-IC,"
the name of this acid H2SO4,
is sulfuric acid.
Notice we did not
put Hydro at the beginning
of the name of
this particular acid.
That's because we only use
hydro when the acid does not
contain an oxygen.
If the anion contains an oxygen,
and the anion's name
ends in "-ITE,"
then we name those acids
by changing that ending
of "-ITE" to "-OUS."
For example, H2S03 would be
called sulfurous acid
since S03 2-
is the polyatomic ion sulfite,
ending in "-ITE."
You might have noticed
that sulfate and sulfite
became sulfuric
and sulfurous acids.
For certain polyatomic ions,
we have to add back a syllable
to name the acid.
Phosphate is another example.
It becomes phosphoric acid.
But for other examples,
like nitrate to nitric acid,
we only have to add the ending.
It takes some practice,
but you'll get the hang of it!
For now just keep these
naming rules in mind
as we head back to the classroom
where our students
are investigating
some properties
of acids and bases.
>> professor: Has anyone heard
of the term indicator
when talking about
acids and bases?
>> student: Yeah, I remember
we talked about that
in one of my middle school
science classes.
I think it was a piece of paper
that changed colors.
>> professor: Good, it sounds
like you got to work with
litmus paper at some point.
Do you remember what the purpose
of the litmus paper was?
>> student: Um, I think
it changed colors
when it was an acid,
or maybe it was a base...
maybe it was both?
I don't exactly remember.
>> professor: it's fine
that you don't remember exactly
because we're going to get
to practice with it today.
There are several types
of indicators we can use
to "indicate" whether or not
a substance is an acid,
or a base, or neither.
Litmus paper
is just one of them.
You can put a drop
of a substance onto
red litmus paper
and if its color changes
to blue, you know
the substance is a base.
If there's no color change,
you can try putting a drop
of that same substance
on blue litmus paper
and if it changes to red
you know you have an acid.
There are also what we call
natural indicators,
and you're going to get a chance
to create one
and use it to test
various household items today.
This sounds a bit unusual,
but red cabbage juice
works as a natural indicator
because its color will change
depending on whether or not
the substance it's immersed in
is an acid or a base.
What I'd like for you
to do first is create
some red cabbage juice.
To do that,
you're going to cut up about
four or five large pieces
of red cabbage
into small pieces
and place them in one of
the thousand milliliter beakers.
And then cover it
with distilled water.
You'll heat the solution
until it boils for about
four or five minutes,
and then pour off
the red cabbage juice
and allow it to cool
for about 15 minutes.
We'll be able to use
the cabbage juice to predict
whether or not these household
items are acidic, or basic,
or neither.
So I want you to prepare
your cabbage juice.
After it's made,
we'll test our items
systematically.
You'll test each item
with the red litmus.
If it doesn't change
the paper's color,
you'll then test it
with the blue litmus.
You'll need to write down
your observations as you go,
because after all the items
have been tested with litmus,
I want you to test
each of them
with the cabbage juice.
Finally, you'll create
a color key
for the cabbage juice indicator
based off the observations
you made with the litmus.
The items we'll test today are:
You'll need to label
each of the six cups
with the different substances
you're testing.
Then cover the bottom of
the cup with each substance.
For the baking soda,
add enough distilled water
to make a paste.
You'll test each substance
with the litmus paper.
When testing the solutions
with the cabbage juice,
you'll want to pour
an amount of cabbage juice
equal to the amount of the
substance you have in the cup.
>> student: Oh, baking soda.
>> professor: Then you'll want
to write down your observations
in between each sample.
>> student: That's baking soda.
>> host: It looks like
our students
are already started.
So now is a good time
to take a break and let you
begin this lab.
Instructions
and material lists
can be found in the
"Chemistry Matters Toolkit."
When you're done,
and you've both recorded
and analyzed your results,
I'll see you at the top of
the next video
to compare them
with the results
of our students.