Which of the following anions is
not usually tested for by using concentrated sulfuric acid? (A) Nitrate, NO31−; (B) iodide,
I1−; (C) chloride, Cl1−; (D) sulfite, SO32−; or (E) bromide, Br1−.
There are a variety of qualitative
tests in chemistry that can be used to indicate the presence of specific ions in
substances. In the presence of particular
anions, these tests produce very visible results. A color change, new odor or gas,
temperature change, or formation of a precipitate are all examples of these
observable changes. There are several compounds used to
test for different anions, but our question asks about the reagent, concentrated
sulfuric acid. The correct sequence to test for
anions is first adding dilute hydrochloric acid, then concentrated sulfuric acid,
and finally a barium chloride solution.
Let’s have a look at the ions that
can be detected with each testing reagent to determine which anions are not detected
by sulfuric acid. Typically, dilute hydrochloric acid
produces visible reactions when carbonate, sulfite, bicarbonate, sulfide,
thiosulfate, and nitrate ions are present. Concentrated sulfuric acid is then
used to test for halide ions, such as fluoride, chloride, bromide, and iodide ions,
as well as nitrate ions. Finally, barium chloride is used to
test for the presence of sulfate and phosphate ions.
This question is asking us which of
the anions’ presence would not usually be tested with concentrated sulfuric
acid. Since nitrate, iodide, chloride,
and bromide ions are all tested using sulfuric acid, we can eliminate answer choices
(A), (B), (C), and (E).
Sulfite ions are generally tested
for by using dilute hydrochloric acid. Therefore, the anion that is not
usually tested for by using concentrated sulfuric acid is answer choice (D):