There are a variety of different kinds of chemical reactions
that we learn about.
We know about acid-base reactions.
You know about solubility and about how salts fall to the bottom
and form precipitates.
There's a category of reaction involving metals that's less familiar
to folks, but actually is pretty darn important.
It's the simple question of what happens when you throw
metals into water.
There are actually four different categories of this thing
called a displacement reaction.
A displacement reaction in which you throw metal into water
will have the following results:
The metal will be turned into a cation, the water will be turned
into a base, a hydroxide, and then hydrogen gas will be evolved.
And the most famous of those examples,
throwing sodium and lithium into water makes a big explosion
even in cold water and the solution turns pink from
phenoltheline being in there because of the hydroxide ions
and that explosion is hydrogen gas.
As you move across the periodic table, you move from the most
active metals like lithium and sodium to a second category of metal
which is the alkali earth metals and those are the kinds of things
than can react even in hot water, and then there's a whole suite
of metals in the periodic table, transition metals,
which dissolve in acid.
You're all familiar with this.
If you throw iron into water that is acidified you end up dissolving
the iron away.
Well we're going to do that experiment here,
only we're going to use zinc as a transition metal and
we're going to use zinc in particular because zinc finds a
substantial amount of use in coins and I'm going to be
showing you another demonstration in which you get to watch
what happens when you pour hydrochloric acid onto a penny.
It's kind of interesting.
So let me go ahead and pour the acid in and you'll notice
the foaming occurring.
This foaming is from the evolution of hydrogen gas while
the zinc metal is being oxidized to zinc ion and the solution
is turning basic.
Now, if I was to capture the evolving gas by putting a balloon
over the top of it and then tie it off, I could light off that balloon
and I would see a pop coming from the hydrogen gas
that had evolved.
So this is an examle of a displacement reaction and
this is an example of a metal which is not so reactive
that it dissolves in water, it is not so reactive that
it dissolves in hot water, but is in that category where if you
dump it into acid, in particular hydrochloric acid here,
you'll be able to get it to dissolve away.