Video Transcript
When testing for halide salts, a
few drops of concentrated sulfuric acid are carefully added to the solid salt
crystals. Which of the following salts would
you expect to produce purple-colored fumes? (A) Potassium bromide, KBr, (B)
potassium chloride, KCl, (C) potassium iodide, KI, or (D) potassium fluoride,
KF.
The addition of concentrated
sulfuric acid can be used as a qualitative test. This qualitative test visibly
detects the presence of halide anions. When sulfuric acid is used to
detect halide ions in unknown salts, the acid is added dropwise and the results are
observed. Halide salts in the presence of
concentrated sulfuric acid will produce fumes of varying appearance depending on the
halide.
If the salt contains fluoride or
chloride ions, the reaction with sulfuric acid will produce colorless fumes. Salts containing bromide ions will
produce orange-brown fumes. Iodide ions will produce
purple-colored fumes.
Let’s have a look at our answer
choices. All of the given salts contain
potassium as the cation. However, the only salt that
contains iodide ions to generate purple fumes would be potassium iodide. Therefore, the salt that would be
expected to produce purple-colored fumes when testing with concentrated sulfuric
acid would be answer choice (C) potassium iodide, KI.
