Why do fireworks give different coloured flames?
Why do fireworks give different coloured flames?
PROF WAQAR HUSSAIN
The
composition and manufacture of fireworks are trade secrets, but such substance
consists of inflammable powder mixed with salts which gives distinct colours to
the flame. Salts are compounds consisting of metal cations and non- metallic
anions joined by ionic bonds. These metal cations are responsible for imparting
colours to the flame when excited at high temperature.
Thus strontium salt gives red colour, barium salt gives grassy green colour, copper salt gives bluish green colour, calcium salt gives orange colour, potassium salt gives violet colour, sodium salt gives golden yellow colour, etc. Iron filings produce sparks, as in squibs. When cracker explodes, heat is generated which heats up the salts and the matal cations excite and give different colours .The electron of above mentioned six metals cations are excited to higher energy level(orbit) by absorbing heat energy. These electrons can stay in higher orbits for a smaller period of time (about a nano second i.e.10-9s) and then return. When their electrons come back to their original orbits, they emit absorbed energy in the form of radiations. As atoms of different metals require different energies for jumping to higher levels as different metal cations have different energy levels between their orbits consequently, on returning to their original orbit, they emit different energies and hence different radiations. As these different radiations have different energies thus different wavelengths and hence emit different colours corresponding to their wavelengths. That is why! We see different coloured flames in firework. Another important thing, about six metal cations require a temperature of about 400 oC for excitation of electron and hence they impart colour to the flame. Other metal cations require very high temperature (about 3000 oC) for excitation of electrons. Hence, they do not give colour to flame.
Thus strontium salt gives red colour, barium salt gives grassy green colour, copper salt gives bluish green colour, calcium salt gives orange colour, potassium salt gives violet colour, sodium salt gives golden yellow colour, etc. Iron filings produce sparks, as in squibs. When cracker explodes, heat is generated which heats up the salts and the matal cations excite and give different colours .The electron of above mentioned six metals cations are excited to higher energy level(orbit) by absorbing heat energy. These electrons can stay in higher orbits for a smaller period of time (about a nano second i.e.10-9s) and then return. When their electrons come back to their original orbits, they emit absorbed energy in the form of radiations. As atoms of different metals require different energies for jumping to higher levels as different metal cations have different energy levels between their orbits consequently, on returning to their original orbit, they emit different energies and hence different radiations. As these different radiations have different energies thus different wavelengths and hence emit different colours corresponding to their wavelengths. That is why! We see different coloured flames in firework. Another important thing, about six metal cations require a temperature of about 400 oC for excitation of electron and hence they impart colour to the flame. Other metal cations require very high temperature (about 3000 oC) for excitation of electrons. Hence, they do not give colour to flame.
When heated, different chemicals give off different colors. firework display
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