Video Transcript
Some students put some copper into
a test tube of hydrochloric acid. They notice that the copper metal
stays at the bottom of the test tube and that it does not react with the
hydrochloric acid. Which of the following statements
correctly describes the results of this experiment? (A) No reaction happens because
hydrochloric acid cannot react with any pure metal elements. (B) The copper does not react with
the hydrochloric acid because copper is less active than hydrogen. (C) No reaction happens because
copper is incredibly unreactive and it does not react with any other chemical
substance. (D) The copper does not react with
the hydrochloric acid because copper is more active than hydrogen. (E) The copper does not react with
the hydrochloric acid because it has been cut up into small pieces.
This question is asking us why
copper, a type of metal, does not react with hydrochloric acid, which is a type of
mineral acid often used in chemistry laboratories. Let’s clear some space to discuss
why copper doesn’t react with the acid. Metals can react with acids in a
substitution reaction. A substitution reaction takes place
when an active element replaces a less active element in a chemical compound. In the case of a metal reacting
with an acid, when a reaction takes place, an aqueous salt and hydrogen gas are
produced.
To explain why copper does not
react with hydrochloric acid, we need to consider the series of chemical
activity. The series of chemical activity
shows which elements are more active than others. The more active elements are found
at the top of the series, and the less active elements are found at the bottom. We can see from the series of
chemical activity that copper is less active than hydrogen because it is lower on
the series. Because copper is less active than
hydrogen, it will not be able to take the place of hydrogen in the hydrochloric
acid. And therefore no reaction will take
place.
If we were using a different metal,
such as magnesium, instead of copper, a reaction would take place. Magnesium would take the place of
hydrogen in the hydrochloric acid. And an aqueous solution of
magnesium chloride salt and hydrogen gas would be produced. We would observe bubbling as the
hydrogen gas is released from the solution.
Now, let’s think about all of this
information we’ve discussed and take another look at our answer choices. The statement which correctly
describes the results of the students’ experiment is answer choice (B). The copper does not react with the
hydrochloric acid because copper is less active than hydrogen.
