Video Transcript
The following figure shows what
happens when some aluminum foil is put into a beaker of hydrochloric acid. Why are lots of gas bubbles
produced during this chemical reaction? (A) Steam is produced as the
aluminum replaces hydrogen in the hydrochloric acid. (B) Oxygen gas is produced as the
aluminum replaces hydrogen in the hydrochloric acid. (C) Hydrogen gas is produced as the
aluminum replaces hydrogen in the hydrochloric acid. (D) Nitrogen gas is produced as the
aluminum replaces hydrogen in the hydrochloric acid. (E) Carbon dioxide gas is produced
as the aluminum replaces hydrogen in the hydrochloric acid.
When a chemical reaction takes
place, a number of observations can be made. For example, we might see a color
change or smell vapors being given off. We may also see gas bubbles being
produced, which we call effervescence in chemistry. When looking at the diagram, we can
clearly see that a chemical reaction is taking place between the aluminum foil and
the hydrochloric acid, because lots of gas bubbles are being produced. Let’s clear some space to discuss
the chemical reaction that is occurring.
When a metal reacts with an acid, a
salt solution and hydrogen gas are produced. In this problem, the salt produced
will be aluminum chloride, or AlCl3. The aluminum comes from the
aluminum foil, and the chloride ions come from the hydrochloric acid, which has the
chemical formula HCl.
Let’s write a word equation to
represent the chemical reaction. Let’s begin by writing aluminum
plus hydrochloric acid, which are the names of the reactants. After the reaction arrow, we can
write aluminum chloride plus hydrogen gas, which are the names of the products. It would help us to also write a
reaction equation using chemical symbols. This reaction is an example of a
substitution reaction. In a substitution reaction, a more
active element replaces a less active element in a compound.
The series of chemical activity can
help to determine which elements are more active than others. Elements that are higher up on the
series are more active than those that are lower down. Aluminum is higher on the series
than hydrogen, so it is more active than hydrogen. This means that aluminum can
replace hydrogen in the hydrochloric acid.
Now, let’s use what we have learned
to select the correct answer choice. The answer choice that best
explains the changes that occur during the chemical reaction is answer choice
(C). Hydrogen gas is produced as the
aluminum replaces hydrogen in the hydrochloric acid.
