Video Transcript
Which of the following is not commonly associated with nitric acid? (A) It is used in the manufacturing of fertilizers and explosives. (B) It can be prepared by heating potassium nitrate and concentrated sulfuric
acid. (C) It is a strong oxidizing agent. (D) It is a weak acid, only partially dissociating in water. (E) It produces a red color when adding a few drops of litmus solution.
In order to answer this question, we need to identify the statement that is
false. Let’s begin by looking at how nitric acid can be produced in a laboratory
setting. Potassium nitrate and sulfuric acid react when heated to produce nitric acid and
potassium sulfate. We can also write a balanced chemical equation for this reaction. Answer choice (B) is therefore incorrect because it is true that nitric acid, or HNO3
aqueous, can be prepared by heating potassium nitrate and concentrated sulfuric
acid.
Since we know now how nitric acid can be made, let’s take a look at its
properties. When nitric acid is added to water, it completely ionizes. Every unit of nitric acid dissociates into H+ ions and NO3− ions in the aqueous
solution. This means nitric acid is a strong acid. Therefore, answer choice (D) is false and must be the correct answer because it is
describing a weak acid. But let’s explain why the remaining answer choices are true statements.
Here is another chemical equation to represent nitric acid dissolving in water. When a nitric acid molecule dissociates in water, a hydrogen ion combines with a
water molecule to create the hydronium, or H3O+, ion. When hydronium ions come into contact with a blue litmus solution, it turns red,
indicating that the solution is acidic. Therefore, answer choice (E) is incorrect because it is a true statement.
Now nitric acid is corrosive to metals, especially in its concentrated form. For example, concentrated nitric acid can act as a strong oxidizing agent in
reactions with metals, such as the one shown here with copper metal. We can see here that the oxidation number of nitrogen changes from positive five to
positive four. This means that during the reaction, nitric acid gets reduced by gaining electrons
from another species. It is therefore the oxidizing agent. The oxidation number of copper changes from zero to positive two. Copper loses electrons during the reaction, so we say that it gets oxidized. Since statement (C) is a true statement, we can also eliminate it.
Finally, nitric acid is used in the production of fertilizers and explosives. More specifically, nitric acid is used to produce ammonium nitrate by reacting it
with ammonia. Ammonium nitrate is an essential chemical used in the manufacturing of fertilizers
and explosives. So now we see that statement (A) is also true and can be eliminated.
In conclusion, the statement about nitric acid that is not true is statement (D): it
is a weak acid, only partially dissociating in water.
