Flame Test

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Title:
Flame Test

Aim:
To determine the cation in each of the unknown substance X, Y and Z by observing the flame colour of different metal compounds.

Introduction:
A distinctive feature of many s-block metals is their ability to produce flame colours. At temperature of a Bunsen flame, a compound will decompose to give gaseous atoms of its constituent elements. When an electron in the gaseous atom absorbs energy from the flame, it will move from an orbital with lower energy to an orbital with higher energy. When such an electron returns from an orbital of higher energy to an orbital of lower energy, a photon with energy equal to the difference in energy of the two orbitals will be emitted. An emission line results. Each element has a unique emission spectrum. A metal can be identified if it has a strong emission line in the visible region of the electromagnetic spectrum. Thus

when a compound such as NaCl is vaporized in a flame, ion pairs are converted to
gaseous atoms. Na(g) atoms are excited to high energies, and 589nm (yellow) light
is emitted as the excited atoms revert to their ground state electronic configurations. Therefore, the cation in the unknown substances can be identify.

Chemicals:
Concentrated Hydrochloric acid (about 10 cm3)
The following solids (0.1 g) for flame tests:
Barium chloride
Calcium chloride
Copper (II) chloride
Magnesium chloride
Potassium chloride
Sodium chloride
Unknown solids containing a single cation and labelled X, Y and Z

Apparatus:
Bunsen burner
Insulation mat
Platinum wire (or Nichrome wire),
Watch glass

Safety precaution:
As concentrated hydrochloric acid is corrosive, skin contact should be avoided. It is preferable to use polythene gloves and wear goggles while handling it.
Copper (II) chloride and barium chloride are highly toxic by ingestion. Avoid contact with eyes and skin.
When Busen burner is not being used, close the air hole so that you can see the...
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