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Let's spend some time talking about single replacement reactions. As you may have already
noticed, the single replacement reaction occurs when one element, which is represented by
"A" is involved in a reaction with another compound. In this example equation, "A" is
representing an element, and "BX" is the compound. In most single replacement reactions, this
single element is a metal. The "BX"being a compound is made up of a metal and a nonmetal.
Now, if you look at what happens as the reaction progresses, you'll notice that A, which was
our previously single element, is now combined with the original nonmetal X. And B has been
basically kicked out and is now on its own. So in a single replacement reaction, you always
begin with an element plus a compound. The reaction occurs, a new element is by itself,
and a new compound has been created. When metals are involved in these single replacement
reactions, it depends upon the metal's reactivity. A less reactive metal can not replace a more
reactive metal in the compound. Looking specifically at what we call the "Activity Series of Metals,"
it simply arranges the most common metals in order of more reactive down to the less
reactive. The elements at the top of the list are considered the more reactive metals. They
are very willing to donate an electron or two in order to become bonded with another
nonmetal so that they reach their stability level. The activity series is useful for us
because we can look at the list of metals to determine whether a single replacement
reaction will occur. Take a look at Nickel. Nickel can only replace elements that are
below it on the periodic table. Nickel would not be able to replace anything above it.
Lithium is the most reactive metal we have on our Activity Series. Lithium will replace
everything below. Let's look at a couple specific examples. My first single replacement reaction
show magnesium being combined with zinc nitrate. If magnesium is more reactive than zinc, the
reaction will go ahead and happen. Magnesium will be able to replace zinc in the reaction.
Looking at the chart, I see that magnesium is indeed above zinc, so the new compound
formed will be magnesium nitrate and zinc metal will be replaced and will now be the new lone element in the chemical reaction.
The next equation that is starred below is magnesium with Lithium nitrate. You look and
find magnesium and lithium on the Activity Series chart. You'll notice that lithium is
all the way at the top. This reaction will not happen because lithium is above magnesium,
therefore magnesium is not reactive enough or powerful enough to remove lithium from
its bond with nitrate. We'll spend some time experiment with this in lab and the next few
days. You'll get some samples at the bottom that we'll be testing. We won't be testing
sodium because it's explosive in the presence of cold water. You'll test the variety of
metals to determine which one is the most reactive, and then fill in your list in order
of reactivity with the rest as they decrease in reactivity. We'll test this using cold
water, hot water, cold HCl, and hot HCl. With the idea being that if a metal reacts with
the cold water, it is very reactive. It is less reactive if we need the warm water, less
reactive yet if it takes cold HCl, or hot HCl to create a reaction. We'll talk more
specifically about the procedure we'll be using in lab when we meet again in class.
That was just a brief introduction to the investigation we'll be completing in lab,
as well as some more details about single replacement reactions and the Activity Series
of Metals, which really drives whether or not those reactions happen.