Stoichiometry Lab

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Hestia Livana
Partners : Rachel Gideon, Joy Boake, Hannah Harper

Various Color of Light as the Effect of Electron Emission

Objective
Observe the characteristic colors produced by certain metallic ions when vaporized in a flame. Identify the unknown metallic ions by means of its flame tests.

Background
When atoms absorb energy, electrons move into higher energy levels, and these electrons lose energy by emitting light when they return to lower energy levels. Energy levels are fixed energies that electrons can have. Ordinary light is made up of a mixture of all the wavelengths of light. Light, consisting of waves consists of wavelength and frequencies that are inversely proportional to each other, so as the wavelength of light increases, the frequency decreases. However, the light emitted by atoms consists of a mixture of only specific frequencies. Each specific frequency of visible light emitted corresponds to a particular color. The emission spectrum of each element is like a person’s fingerprint. Just as no two people have the same fingerprints, no two elements have the same emission spectrum. In the same way that fingerprints identify people, atomic emission spectra are useful for identifying elements.

Materials
1. Bunsen Burner with tubing
2. Striker
3. Spot plate
4. 2 Wood splints
5. Metallic solution samples (Barium, Calcium, Lithium, Copper, Potassium, Sodium, Strontium, Unknown A, and Unknown B) 6. Cobalt glass
7. Small beaker of water

Procedure
1. Tie back any long hair and put on safety goggles.
2. Fill the beaker of water halfway. This will be used to distinguish the flame following each individual test. 3. Obtain wood splints from the teacher and add a few drops of each metallic solution to the 12-division pot strip. Be sure to not contaminate the solutions and keep them in order so that it is easier to keep them straight. 4. Ignite the burner and place it close to the middle of the work area, not on the edge and make sure to not leave the burner unattended. 5. Test each sample by holding the wood splint towards the side of the flame and recording its color. Do not burn the wood for a long period of time. Instead, reuse the splint. 6. Note that when testing potassium, the color is often hidden by contamination from the table salt in the environment. A blue filter, known as cobalt glass, is used to remove the sodium flame and allow the experimenter to observe the Potassium flame. Watch the flame through the previously obtained sheet of cobalt glass. 7. Using the results of other solutions, test and identify the unknowns. 8. When the lab is complete, turn off the burner, leaving the burner and striker at the work area as well as the beaker. Bring the cobalt glass back to the plastic container. The spot place needs to be placed in the beaker labeled “used” on the table from where it was originally obtained. Clean the work area; putting used wood splints in the trash and pouring the water down the sink.

Data
The Metallic Ion Solutions and the Flame Colors Shown as a Result of Atomic Emission
Metallic Ion Solution| Metallic Ion Solution|
Barium| Yellow-green|
Calcium| Red-orange|
Lithium| Hot pink|
Copper| Coral Pink|
Potassium (without Co glass)| Coral|
Potassium (through Co glass)| Light purple|
Sodium| Yellow-orange|
Strontium| Pink-red|
Unknown A| Orange-red|
Unknown B| Yellow-range|

So, we can conclude that :
* Identity of Unknown A: Calcium
* Identity of Unknown B: Strontium

Discussion Questions
1. What ion can easily mask a Potassium flame? How is this problem addressed? Ion that can easily mask the potassium flame is table salt. The problem is addressed take and observe the potassium with a square of cobalt glass and the potassium without a square of cobalt glass. Cobalt glass will filter and remove sodium flame and make observer able to see...
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