Video Transcript
Which of the following reagents can
be used to detect ammonia gas? (A) Hydrochloric acid, (B) sodium
hydroxide, (C) ammonium chloride, (D) copper(II) oxide, or (E) sodium nitrate.
In this question, we need to
determine which reagent listed is best suited to detect ammonia gas.
Nitrogen gas is abundant in the
air. It is used to form many important
compounds and chemicals. One of the most common is ammonia
gas, NH3. Ammonia gas is used in various
applications, one of the most important being in the production of fertilizers. Ammonia gas can be synthesized in
the laboratory using a mixture of ammonium chloride, NH4Cl, and calcium hydroxide,
Ca(OH)2. And in industry, it is synthesized
by the Haber–Bosch process from nitrogen gas, hydrogen gas, high temperatures and
pressures over an iron catalyst.
Ammonia is colorless. So how can we detect that it has
been produced? The question asks us how it is
detected. We can test if it has been produced
during this reaction using hydrogen chloride. We can dip a glass rod into
concentrated hydrochloric acid and hold it near the mouth of a vessel containing
what we suspect is ammonia gas. If we allow the vapor produced from
concentrated hydrochloric acid, HCl, to mix with the gas produced from the reaction,
a dense white vapor will form if the gas is ammonia. The reaction that forms these
vapors is shown below. The white vapors consist of tiny
solid ammonium chloride particles, which are white.
So, which reagent can be used to
detect ammonia gas? The answer is (A), hydrochloric
acid.
