Hi. It's Mr. Andersen and this is chemistry essentials video 30. It's on neutralization reactions.
Or we sometimes refer to these as acid-base reactions. And to really understand it, you
have to understand one of the most abundant elements in the universe. 90% of atoms are
actually hydrogen. Hydrogen is 1 proton and 1 electron. Remember the proton has a positive
charge. Electron has a negative charge. And so if we take away that electron, what are
we left with? A proton. And so you'll hear these used interchangeably. A hydrogen ion,
which is going to have a positive charge or a proton. Those mean essentially the same
thing. And they're both incredibly important when we're talking about neutralization reactions.
And so water is amphoteric. And what that means is it can either act as an acid or a
base. And more specifically it can act as a Bronsted-Lowry acid or a Bronsted-Lowry
base. What does that mean? Well a Bronsted-Lowry acid is going to donate a proton to a base.
In other words the acid always donates the proton to the base. And this is the best definition
for what an acid and a base is. And so when these, when this proton is transferred, we
call that a neutralization reaction. And so this only occurs in aqueous reactions. And
we also have to be able to identify what's the acid, what's the base. In other words
what is this conjugate acid-base pair. And also using this definition, you should be
able to figure out the strength of acids and bases. Or at least what that strength means.
And so water is really interesting on a number of different levels. But one of the reasons
it's interesting is if you have enough water around water it will actually start to transfer
protons. In other words there's going to be a negative charge here and a positive charge
on the protons. So sometimes one of those proton will actually move over. And so what
you create is hydronium ion, which has a positive charge. And hydroxyl ion, which is going to
have a negative charge. And so using the Bronsted-Lowry definition of what an acid and a base is,
what we're doing is we're taking the acid in this case and the base and we're transferring
a proton from the acid to the base. And so that's how we define what an acid or a base
is. What's interesting about water is it can serve both as an acid and a base. So where
does this definition come from? Well there were two scientists, Bronsted in Denmark and
Lowry in England. And they both kind of identified this at the same time. So they give them both
credit when they named it. And so what you're doing is you're taking an acid and a base
and you're transferring that proton from the acid to the base. And so another way to write
it would be the acid, which has the proton. And then we're transferring that proton, in
this case, to the base. And so we're taking an acid and a base, combining those together.
This is called neutralization. And we're making a conjugate base and a conjugate acid. Now
this is a reversible reaction. In other words it can run in both directions. And that's
why we have the arrow pointing both ways. And so an example of this could be acetic
acid with water. And so if we have acetic acid and water, what we can do is we can actually
take that proton from the acetic acid. And then we can donate it to the water itself.
In this case then, acetic acid is the acid and water would be the base. And so what's
interesting about water is it can serve as both an acid and a base. And so take a moment,
for just a second, and figure out is water an acid here or a base? Is it an acid here
or is it a base? And so you have to go back to that definition. All we say an acid is
is something that's donating a proton. And all we say a base is is something that's receiving
it. And so in this first reaction we're taking hydrochloric acid and water. Have you figured
out which one it is? Well the acid is going to be the hydrochloric acid. The base is going
to be the water. The water is receiving that proton. And so it's the base. And so what
we're doing is we're losing that proton from the hydrochloric acid. And that's making a
conjugate base, chloride. And we're gaining that electron, or excuse me, gaining that
proton in the water and we're making a conjugate acid. So if we look down here we've got ammonia
and water. In this case the water is serving as an acid. Because it's donating the proton.
And who's receiving it is going to be the ammonia. And so that's creating a conjugate
acid and a conjugate base. And so when we're talking about strong acids, or strong bases,
what does that really mean? Well let's look at something that's completely strong. That's
hydrochloric acid. And so if we had hydrochloric acid to water it's going to completely break
apart. In other words all the protons are going to break apart. All the chlorine ions
are going to break apart. And so we call this a strong acid because the arrow you can see
is all running in one direction. Now this proton doesn't just float around. It's going
to quickly combine with water to make hydronium. You just don't have free protons inside there.
But this would be a strong acid. If we look at something that's a medium acid, that would
be acetic acid. So we're going to be transferring protons to the water but we're also going
to be moving those back to the acid itself. So this would be an arrow in both directions.
Or it we were to look at bicarbonate down here. Bicarbonate is going to be more of that
accepting of the proton. And so we call that a real weak acid. But we could also all the
arrow on the other side. And so as you increase the strength of an acid, we're clearing decreasing
the strength of a base. And vice versa. And so that's the Bronsted-Lowry model of what
an acid and a base is. And how we can figure it out in a neutralization reaction. And so
did you learn the following? To identify what's the acid, what's the base. And figure out
these pairs. Well remember just look for where the proton is going. Where it's headed to.
And that's going to tell you what's the acid. What's the base. And I hope that was helpful.