Chemistry Lab

Emission Spectrum Lab
Name: Yue Wai Ming
IB HL Chem Miss Vick

Aim: The purpose of this exercise is to measure specific atomic emission spectra and to
observe the existence of bright line spectra.

Hypothesis: Some elements, especially metal compounds usually give off light in a visible spectrum when heated in flame. This heat will cause some of the electrons in the atoms to be excited and the electrons will jump off to higher valence shells. After this happens, the excited electrons will jump back down to their normal shells as they are unstable and return to their ground state. Because of this, it will release the extra energy in a form of radiation of a certain frequency. This causes the release of light. The colour of the flame will depend on the energy needed for the electron to bounce back faster or slower. This light is determined by a spectrometer looking here at the emitted photon??™s wavelength. My prediction is that the colours the metallic ion produces depend on how far away the wavelength is. The further the wavelength, the darker the colour (darkest being red).

Variables:
Independent Variable: The type of metal compounds used for heating

Dependent Variable: Measuring the Wavelength of each flame
)

Controlled Variable: All the metals have to be combined with chloride

Why is has to be controlled:-
There is a reason for using chlorides for all compounds. This is because when we heat up the compounds, the chloride will not interfere with the flame colour as it does not produce its own colour. There are no excited states for chlorine that emit in the visible part of the electromagnetic spectrum.

Materials-

Spectrometer
|Glass Rod |Copper Chloride |
|Distilled water |Lithium Chloride |
|Bunsen Burner |
|Calcium Chloride |
|Strontium Chloride |
|Sodium Chloride |Paper towels for cleanup |
|Barium Chloride |Safety goggles |

Safety

??? Wear goggles or risk sitting out the lab
??? Do not allow chemicals to touch bare skin: wash well with water immediately if you touch anything accidentally
??? Use caution with the burner, it is very hot!
??? Wash your hands with soap and water after handling the chemicals
Results Table
|Metals |Colour Of Flame |Wavelength (Angstroms) | |
|Barium Chloride |Bright Orange |6000 | |
|Lithium Chloride |Red |6800 | |
|Copper Chloride |Bright Green |4500 | |
|Strontium Chloride |Red |6300 | |
|Potassium Chloride |Orange |6000 | |
|Calcium Chloride |Yellowish Red |6400 | |
|Fluorescent Light |- |5500 | |
|Visible Light |- |5000 | |

Method
1. Gather Equipments to table
2. Cut a strip of wire ( 3cm )
3. Tie a loop on a wire
4. Attach it on the glass rod
5. Turn on the Bunsen burner ( set it to blue flame )
6. Use the glass rod to take the metal compounds
7. Place the glass rod into the flame
8. Use a spectrometer to observe the wavelength of the metal compounds of the flame
9. Observe the colour of the flame.
10. Wash the glass rod with water and burn it with the flame to burn out all impurities.
11. Record your results
12. Repeat steps 5-9 for the rest of the metals

In doing so, it will release the extra (excess) energy in the form of electromagnetic radiation of certain frequency

Conclusion- Based on my results, my hypothesis state was sort of going on the right track but I forgot to add in the trend of the results given. The trend is that when we move down a group, the colour of the flame will change and the wavelength of the compounds will decrease. However when we move across a period, a decrease in wavelength occurs.

Evaluation of method: For this experiment, things that my group did to ensure accuracy were to wash the wire from the wooden splint every time we finish a recording. We do this because we want to clean up so that that our next test won??™t be affected by it. For example, we used Strontium Chloride first, after using it we cleaned it and then only we picked up the calcium chloride. We would either use a different wire strip when collecting another metal or we would just wash it. We ensured precision by rounding up the wavelength to angstrom units. This would give us a more accurate result. We also rounded up to 2 decimal places. For example for calcium chloride we got 6.43 nm. We rounded it to 6.4 and changed it to 6400 angstrom. The controlled variables were kept very accurate as all the compounds that we used for this experiment was with chloride, s it was all good. Improvements that we would make to the experiment next time are that we could use a new piece of wire each time while we were collecting a different compound. This is because we usually had trouble when starting with new compounds because of the impurities or contaminants which affected the colour of the flame and our results.