Video Transcript
The following figure shows a beaker
of aqueous hydrochloric acid and five different types of metals. Which metals form a salt when
reacted with the hydrochloric acid solution? (A) Magnesium, sodium, and
potassium; (B) copper, sodium, and magnesium; (C) copper and gold; (D) sodium and
gold; (E) copper and magnesium.
Some metals are highly active and
tend to react with many other substances. Other metals are less active. The series of chemical activity
describes differences in the activities of substances. It lists substances from top to
bottom in order of decreasing activity. Potassium is at the top of the
series because it is highly active, and sodium is beneath potassium because it is
less active than potassium. Copper and gold are near the bottom
of the series because they are not very active metals. The series of chemical activity
also shows which metals can displace hydrogen in a mineral acid, such as
hydrochloric acid. Metals tend to replace hydrogen in
dilute mineral acids if they are above hydrogen on the series of chemical
activity.
Let’s clear some space to discuss
the type of chemical reaction that will take place.
In a single substitution reaction,
a more active metal replaces a less active element in a compound. In this problem, the compound is an
acid and the less active element that is being replaced is hydrogen. Potassium metal can replace
hydrogen in hydrochloric acid because it is above hydrogen on the series of chemical
activity. Let’s write a chemical equation for
the reaction of potassium metal with the hydrochloric acid solution.
When potassium reacts with
hydrochloric acid, potassium takes the place of hydrogen in the acid. The products are a new compound
called potassium chloride, which is a salt, and hydrogen gas. So, we’ve learned that potassium
does form a salt when reacted with the hydrochloric acid solution.
Now, sodium and magnesium metal are
also above hydrogen on the series of chemical activity. Therefore, when these metals are
placed in the hydrochloric acid solution, a salt and hydrogen gas are produced.
Next, we notice that copper and
gold are below hydrogen on the series of chemical activity. Therefore, these metals cannot
replace hydrogen when placed into the hydrochloric acid solution, because they are
less active than hydrogen. And because no reactions take
place, no salts will be formed. Now we’re ready to take a look at
the answer choices.
In conclusion, the metals
magnesium, sodium, and potassium are more active than hydrogen and therefore form a
salt and hydrogen gas when reacted with hydrochloric acid. Therefore, the correct answer is
answer choice (A): magnesium, sodium, and potassium.
