(bangs)
- Welcome to Real Chemistry, today we're going
to talk about acids reacting with bases.
And an acid, recall, is anything that gives up hydrogen ions
into solution when it's put into water,
just like this hydrochloric acid does, down below.
And a base is anything that gives off hydroxide ions
into water when it's dissolved,
just like this sodium hydroxide down here.
And it turns out something pretty special happens
when you mix hydroxide with those hydrogen ions,
and we're gonna talk about what that is.
Our main goal is to predict the products that will form
when we combine an acid and a base.
So let's go ahead and start with this reaction right here,
what happens when you combine hydrochloric acid
and sodium hydroxide?
First, we're gonna walk through it, sort of conceptually,
and then I'm gonna give you a list of steps to follow
that will always give you the right products.
So remember that when I put HCl into solution,
it splits up into hydrogen ions and chlorine ions.
And when I put sodium hydroxide into solution,
it splits up into sodium ions and hydroxide ions.
And it turns out that what happens is
the hydroxide ions combine with the hydrogen ions,
and when they do that, you get one oxygen and two hydrogens,
and that turns out to be water.
Now water's not an ionic compound,
so you have these two ions combining
to make water, which is a molecular compound.
So whenever you combine an acid or base,
one of your products is water.
The other product you get is a ionic compound.
In this case, we see that we're left
with chlorine and sodium.
Sodium's positive and chlorine's a negative,
and so they hang out together and form an ionic compound.
So when I mix HCl and sodium hydroxide,
I get out water and sodium chloride.
And you always get a water and an ionic compound
when you mix together an acid and a base.
Let's take a look at a few examples
that might differ from this just a little bit,
but follow the same general pattern.
So now we're gonna combine nitric acid,
HNO3, with potassium hydroxide.
Now, notice in this case, we have nitric acid,
which has a polyatomic ion, NO3,
and we just treat that like one ion, like we always do.
So, the very first step
is that you combine the hydrogen ions
and your hydroxides to make water,
so we always get out water.
And that gets rid of our hydroxides.
That's where our hydroxides went, into that water.
That also gets rid of our hydrogen.
And so step two says the remaining ions
form an ionic compound, what ions remain?
Well, potassium remains, and so does nitrate.
And so we just get out potassium nitrate.
Now, the third step says balance the charges.
What does that mean?
Well, when you form your ionic compound,
you need to make sure that it's neutral
'cause ionic compounds should always
be written as neutral compounds.
And, if I take a look, potassium, we know,
has a plus one charge, and nitrate has a minus one charge,
so those are actually already neutral.
We have one potassium at plus one
and one nitrate at minus one, giving us a neutral compound.
So the charges are already balanced,
so we can just write our ionic compound as KNO3,
and that's a neutral one.
The next step is balance the reaction.
Well if you take a careful look,
this reaction's already balanced,
but in the next few problems,
we'll see some reactions that aren't balanced,
and I'm actually gonna leave that step for you to do.
If you need some help balancing the chemical reactions,
check out my video "Balancing Chemical Reactions."
Once you get the unbalanced reactions,
you just follow the steps in that video
to finish the problem.
Okay so that's done, and it turns out to be balanced.
Let's take a look at another acid base reaction.
This time we're combining phosphoric acid
with sodium hydroxide.
When we do that, we once again,
just as always, combine our hydroxides,
and our protons, that is, our hydrogen ions,
to make water, so we get out water.
And we also are gonna get out an ionic compound.
So what ions are left?
Well we have sodium and we have phosphate,
and sodium and phosphate are gonna
combine to form an ionic compound.
So now we've done steps one and two.
So what we need to take a look at now
is balancing the charges in our ionic compound.
So, what I do is I just go ahead and write out
both the ions I have, and we know that sodium is plus one
and phosphate is three minus, now that's something
that you should have memorized, if you don't
have it memorized, though, you can figure it out
from how many hydrogens were paired with phosphate.
Since there were three hydrogens paired
with phosphate originally that tells you
that phosphate must be minus three
to make phosphoric acid neutral.
Okay, so you know that phosphate's three minus
and sodium's one plus.
How do you make that neutral?
Well you can just sort of think about it
and realize, "Hey, I need three sodiums
"to balance out that charge."
You can also do what's called crossing over,
which is where I take this charge down here
to tell me the number of sodiums I have,
and this charge up here to tell me
how many phosphates I have.
And so what that's gonna give me then
is three sodiums for every one phosphate.
And that's a balanced charge.
If you're not sure how to write those balanced charges,
check out my "Naming Ionic Compounds" video,
and I go through in more detail
how you balance those charges.
So that means that we should have three sodiums
with our phosphate, so now,
we're done except for balancing the chemical reaction.
And like I said, I'll leave balancing the chemical reaction
to you, if you need help doing that,
go ahead and watch my "Balancing Chemical Reactions" video.
All right, another reaction we could imagine,
is combining hydrobromic acid, that's HBr,
with calcium hydroxide, what happens there?
Well same thing, we combine our hydroxides,
and our hydrogen ions to make water.
So we get rid of this guy,
and we get rid of this guy, and that makes water.
And then we investigate what ions do we have left over?
So that's step two, what ions do we have left over,
well we have calcium left over.
And we have bromine left over.
So that's gonna form an ionic compound.
Remember, you always need to write the positive ion first,
we always write the cadion first,
or another way to put it is we always write the metal first,
so I'm gonna write CaBr, that always applies
when you write ionic compounds,
you should write the positive thing
before the negative thing.
And now what we're gonna do is step three,
we're gonna make sure the charges
of our ionic compound are balanced.
So we have Ca and we have Br,
and we can predict the charges on those.
If you're not sure how to do that,
check out my video "Predicting the Charges on Ions",
and you can basically do this using the periodic table.
So now we have calcium at two plus and bromine at one minus,
that tells me I need two bromines to balance out my calcium,
that'll give me two things at negative one,
for a total negative charge of negative two,
and that'll balance out my total positive charge
of plus two, again, if you want to,
you can also think about it as crossing over.
And that's gonna give me a calcium Br two . . .
And so there should be a two on our bromine
so that we have a neutral ionic compound,
so that is a completed acid base reaction,
there's some balancing work to be done
before you could be said to have finished the problem.
Again, check out that "Balancing Reactions" video
if you need help with that.
All right, so that is acid base reactions,
when you combine an acid and a base,
you always get out water and an ionic compound.
The main challenge is making sure that ionic compound
is balanced in terms of its charges,
and then balancing the chemical reaction.
If you have any questions, please leave 'em below,
please subscribe to get updates about future videos,
or visit my channel to see other chemistry videos.