Video Transcript
What gas is produced when a metal,
such as magnesium, reacts with hydrochloric acid? (A) Steam, (B) chlorine, (C)
hydrogen, (D) carbon monoxide, (E) carbon dioxide.
In this question, we are told that
the metal magnesium reacts with the acid named hydrochloric acid. The words “reacts with” tell us
that a chemical reaction is taking place between these two substances. Let’s say we placed a piece of
magnesium metal into a test tube containing hydrochloric acid. Pretty quickly, we would observe a
lot of fizzing and bubbling. The test tube would also feel warm
because the reaction gives off heat. These are signs that a chemical
reaction is happening.
What we have observed is a chemical
property of some metals. A chemical property is a
characteristic of a substance that can only be observed during a chemical
reaction. The chemical property we are
observing here is reactivity with acids. Unlike most nonmetals, many metals
tend to react with dilute minerals acids, such as hydrochloric acid.
A metal will only react with an
acid if it is more active than hydrogen. We can use the chemical activity
series to determine if magnesium is more active than hydrogen. An element is more active than
hydrogen if it appears higher on the vertical list than hydrogen. We can see that magnesium is above
hydrogen. So we would expect it to react with
hydrochloric acid.
Now, let’s write a word equation
for this chemical reaction. First of all, we know that the
starting materials or reactants are magnesium and hydrochloric acid. But what are the products? This reaction forms two
products. One product is a salt. A salt is another name for an ionic
compound. In our reaction, the salt formed is
named magnesium chloride. This salt remains dissolved in the
solution in the test tube and is colorless. So we would not even notice that it
was there.
But we do notice that a lot of
fizzing and bubbling occurs. This happens because a gas is being
produced. The gas produced in our reaction is
hydrogen gas. In fact, when a metal reacts with a
mineral acid, it generally produces hydrogen gas. We could confirm that this is
hydrogen gas by using a burning wooden splint test. While the reaction occurs, we can
light a wooden splint and place it just over or slightly inside the test tube. We will hear a pop noise as the
hydrogen gas reacts explosively with oxygen in the air.
In conclusion, the gas that is
produced when magnesium metal reacts with hydrochloric acid is hydrogen. So the correct answer is answer
choice (C).
