Result of Observation

Result of Observation

Chemical name and symbol Physical appearance Cation of the compound Flame color

NaNO3Sodium nitrate Colourless crystal Na+ Yellowish Orange

NaClSodium chloride Colorless crystal Cl+ Yellowish Orange

LiNO3Lithium nitrate Colorless crystal Li+ Red

BaNO3Barium nitrate White crystal BaІ Bright yellow, lime yellow

Sr(NO3) 2Strontium nitrate White crystal SrІ Dark red

Cu(NO3)2Cupric nitrate Blue crystal CuІ Green, bluish green.

Ca(NO3) 2Calcium nitrate White crystal CaІ Redish orange

KNO3Potassium nitrate Colourless crystal. K+ Light purple

Unknown #1 Colorless crystal Red

Unknown #2 White crystal Redish orange

Unknown #1 is lithium nitrate, because it had the same physical appearance and same flame color as lithium nitrate.

Unknown #2 is calcium nitrate, because they share the same physical appearance and flame color.

Discussion

A) Which part of the compound is responsible for the flame colour? How would you know?

The cation part of the compound is responsible for the flame colour. Because almost all of the different compound had nitrate as the anion, but they had different colours. The only compound which did not have nitrate, as the anion is sodium chloride. But it produced the same color as sodium nitrate, which showed that the color in which they produce was caused by sodium.

B) Which sample released the most energy? How would you know?

The sample, which released the most amount of energy, is potassium nitrate. Because the amount of energy light produces is depended on the frequency (colour) of the light, and potassium nitrate produced a light purple colour. According to the visible spectrum, a photon of purple had more energy than any other colour produced in this lab, because purple light has shorter wavelength (approximately 380-450 nm) and shorter wavelength means higher frequency which also means higher energy. Therefore we can conclude that potassium nitrate produced the most amount of energy when burned.

C) How would Niels Bohr explain the different colours of light produced by different compounds?

According to Bohr’s theory and atomic model, electrons can be excited by absorption of light, thus undergoes a transition from a lower energy to a higher energy level. Electrons can also be de-excited by emission of light, thus undergoes a transition from a higher energy to a lower energy level. During this experiment, we excited the electrons which electrons go to a higher energy level, when electron falls back to ground state, they should emit light. In each different element, the wavelength of the emitted or absorbed light is exactly so that the photon carries the energy difference between the two orbits. Since the electron of different elements have different quantized energy, the light they each emit has different wavelength (energies), and this is why we see different colors.

D) Use quantum theory to fully explain your observations.

When we burn the compounds, the electrons get excited, so they undergoes transition from lower energy level to higher energy level, and come back to ground state. When electrons fall back to ground state, they release energy as photon of light. The Quantum Theory states: When an atom emits or absorbs energy in the form of light or other electromagnetic radiation, the energy of the atom cannot change continuously, it can only change by small finite amount, which is called quanta. Also the energy of light or other electromagnetic radiation is quantized. This means that electron can never be found between orbits; in order for an electron to undergo transition, there is a certain minimum amount of energy that is being absorbed or emitted which is characteristic for each metal. Which means all metal have a different value. This explains when different metal are heated they emit light with different frequencies, which also mean different color.

Conclusion

During this lab we investigated the different flame colours produced