My group was given an unknown salt containing three ions, either two cations and
one anion, or two anions and one cation.
We needed to identify one cation and one anion
within the salt from a selection of possible options.
The possible ions in the salt are
listed as follows:
chloride, nitrate, carbonate, sulfate, lithium, potassium, sodium,
magnesium, calcium, strontium, and barium.
We accomplished this task through two experimental techniques.
The first, a
flame test, focused on the color of light emitted when the salt was heated in the flame of a
Different metals, when heated, emit different colors of light.
cation could be determined.
The second test focused on precipitation reactions between
the aqueous solution of the unknown salt and added ionic compounds.
whether or not a solid was formed when each compound was added to the solution, we
were able to determine one anion within our salt, and reinforce our other experimental
data on the cation.
Every element has a characteristic emission spectrum.
When an atom is excited,
as through heat, it absorbs excess energy and the electrons within the atom reach an
When the electrons fall back to their normal state, the excess energy is
emitted as light of various discreet wavelengths.
The discreet wavelengths vary from
element to element.
Thus, the emission spectrum of the atom is produced, and is often
observable as a distinct color of light.
The metals lithium, strontium, potassium,
magnesium, calcium, and sodium each emit a distinct color of light, while the non-metals
being tested do not.