Emission Spectroscopy

...

Data:

Color

Position number

Red

6.5

Orange

6.3

Yellow

6.1

Green

5.6

Blue

4.9

Violet

4.5

Mercury line color

Position #

Violet

4.3

Blue

5

Green

5.6

Yellow

6

Hydrogen line color

Position #

Violet

4.5

Blue

5.1

Red

6.5

Salt

Flame color

CaCl2

Red

BaCl2

Orangey-green

KCl

Light purple

NaCl

Orange

CuCl2

Green

Unknown # 3

Light purple

Analysis:

Part I:

A rainbow can be seen when the sun comes out after a storm because the water droplets act as a prism and separates the different colors the sun light emits causing the color spectrum to be seen.

Part II:

(Calculations on attached page)

For violet, 406.202 nm was calculated and 434 nm was expected. For blue, 476.6827 nm was calculated and 486 nm was expected. For red, 641.137 nm was calculated and 656 nm was expected. Comparing the numbers they are not the same but they are very close. This deviation could be explained by an error in the observers eyesight and focusing skill. If when looking into the spectroscope, 4.5 were seen when really it was 4.7, this would effect the calculations. Also if the position numbers were wrong for the mercury line color test then the y=mx+b formula would be off as well. This would again throw off the calculations.

Part III:

My unknown metal salt was KCl. Both flames were light purple. Designers of fireworks make the explosions have different colors by choosing different metal salts to explode. For example, if the designer wanted a red firework they would use CaCl2. If they wanted a purple firework they would ignite KCl and shoot this metal salt into the air.

Results & Conclusions:

The purposes of this experiment were to look at the colors of elements emitted in flame tests and to be able to identify an unknown metal from the colors and to examine the atomic emission spectra of mercury and hydrogen and use the spectra to find the wavelength of each color emitted.

The objective of this lab was met. The unknown metal salt was discovered with out any complication and the wavelength of each color emitted was found by examining the atomic emission spectra of mercury and hydrogen.

The unknown element ended up being KCl because the light emitted was light purple. The Rydberg equation was used to calculate the wavelengths for the hydrogen lines produced from a hydrogen gas tube. The calculated values were 434 nm for purple, 486 nm for blue and 656 nm for red. A spectroscope was used to view the lines produced from a mercury vapor tube and a hydrogen vapor tube. The colors and positions were recorded. Using the known wavelength values for the four mercury lines a calibration curve was made and used to find the wavelength values for the three hydrogen lines. They were found to be 406.202 nm for purple, 476.6827 nm for blue and 641.137 nm for red.

The difference in calculated and expected wavelength can be explain by the humans inability to see clearly in the spectroscope. This device is small and the numbers are hard to read. It is very possible the position number was misread which would effect the equations. To prevent this from happening, multiple people could look at the position number through the spectroscope and