Whenever any sample salt solution is introduced into the flame, the solvent is vaporized leaving behind tiny particle of solute solid molecules which further on heating are converted into gaseous molecules. These gaseous molecules are then decomposed into the gaseous atoms, some of the gaseous metallic atoms absorb the heat energy from flame and got excited.
The transition of the atoms takes place to higher energy state. Those atoms return to the ground state by emitting the radiations. If we know the amount of radiations emitted and the wavelength of the emitted radiations we can have quantitative and qualitative analysis,
A brief overview of the process:
1. The solvent is first evaporated leaving fine divided solid particles.
2. This solid particles move towards the flame, where the gaseous atoms and ions are produced.
3. The ions absorb the energy from the flame and excited to high energy levels.
4. When the atoms return to the ground state radiation of the characteristic element is emitted.
5. The intensity of emitted light is related to the concentration of the element.
The temperature of the flame must be 2000 K or above. The fraction of the number of the atoms which are excited is given by Boltzmann equation: $$ \frac { { N }_{ 1 } }{ { N }_{ 0 } } =A { e }^{ \left( \frac { -\Delta E }{ kT } \right) } $$ Where, \( { N }_{ 1 } \) = no. of the atoms in the-excited state
\( { N }_{ 0 } \) = no. of the atoms in the ground State.
\( \Delta E \) = \( { E }_{ excited } - { E }_{ ground } \) (Energy of Activation)
\(K\) = Baltzman Constant
\(T\) = Temperature in dag. K
\(A\) = characteristic constant.
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