Hint: The flame test is done in chemistry to determine the metal or metalloids present in an ionic compound. The compound when placed on the flame gives a characteristic colour and emission spectrum. The colour emitted is visible to the naked eye which helps in giving the appropriate result for the flame test.
Complete answer:
There are two important reasons why chlorides are preferred for the flame test. Let’s understand the given reasons:
Metal chlorides are found to be more volatile than other metal salts. When a compound is volatile it quickly evaporates from the solid to gaseous form. Metal chlorides evaporate under the flame and thus give a bright colour. The colour can be used to identify the metal ion.
Chlorine atoms refrain from emitting any energy in the visible region of light.
When the metal ions/ Metal chlorides are placed under the flame, the electrons gain energy. The electrons of the metal atom and the chlorine get excited to reach higher energy levels. These electrons tend to emit the gained energy in the specified wavelength on returning to the ground state. To differentiate the metal atom, the metal atoms emit light in the visible region. However, the chlorine atoms do not emit light in the visible region. So, the flame colour visible is only of the metal alone and hence the metal can be identified.
Following are the flame colours of some Metal chlorides:
| Metal Chloride | Flame Colour |
| Orange | Calcium chloride |
| Red | Strontium chloride |
| Orange-yellow | Sodium chloride |
| Yellow-green | Barium chloride |
Note:
In the flame test, chloride solutions are used. These solutions are prepared by the reaction with HCl. Also, the colour of the flame is not only dependent on the metal ion it is but also on the temperature of the flame. So it is imperative to maintain a standard temperature at all times.
