Quimica

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Absorption of sunscreen product |
January 31, 2012 |
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Boyeong Lee

Partner: Rashed Almansoori
TA: Yunteng He
Lab Section # 22 Tuesday 9-12

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ABSTRACT:
The purpose of this experiment is to find the absorbance level of numerous concentrated sunscreens. According to beer’s law, absorbance is equal to concentration times extinction coefficient times length of the container.The extinction coefficient for Coppertone SPF 15 came out to be 216.39 mol-1cm-1. The more concentrated the solution is, less diluted the solution gets. Compare to other sunscreen product with lower SPF, my number was lower than the average of the class data.
THEORY:
The purpose of this experiment is to figure out the absorption of differently concentrated sunscreen. Sunscreen contains asubstance that is able to absorb Ultraviolet light that is located on electromagnetic spectrum. The absorbance of sunscreen is equal to Concentration multiplied by the length of the container and extinction coefficient. The concentration is also known as the number of molecules per liter. If the sunscreen is highly concentrated, the absorbance should be high. There is no particular unit forabsorbance but in this experiment, g/mL will be used for concentration. Measuring the absorbance of sunscreen leads to discovering the numerous sun protection factor rating. We measure the absorbance of different concentrated sunscreen by neutralizing the solution with different amount of ethanol. The original concentration for sunscreen of Coppertone with SPF of 15 was .0023 g/mL. The differentconcentration was measured by timing the dilution factor of each individual solution with the original concentration. The absorbance was measured by placing the different solution into a spectrophotometer.
Beer’s law is used in this experiment because it states that the absorbance is precisely relative to the concentration of a solution. Absorbance is equal to concentration times extinctioncoefficient times length of the container.
PROCEDURE:
See CH 221, Laboratory Manual, Haak, Winter 2012, pages 28-30
DATA:
.0023 gram of Coppertone SPF 15
The dilution factor and the concentration of each solution were measured:
Tube | mL stock solution | mL 95% ethanol | Dilution factor | g sunscreen/mL |
1 | 5.00 | 0.00 | 1 | .0023 |
2 | 3.50 | 1.50 | .7 | .00161 |
3 | 3.00 | 2.00 | .6 |.0014 |
4 | 2.50 | 2.50 | .5 | .00115 |
5 | 2.00 | 3.00 | .4 | .00092 |
6 | .5 | 4.50 | .1 | .00023 |

The absorption was measured for each solution on spectrophotometer:
Tube | Absorption |
1 | .66 |
2 | .58 |
3 | .57 |
4 | .56 |
5 | .4 |
6 | .1 |

CLASS DATA:
* Coppertone SPF 8: e = 490.12 M-1cm-1
* Hawaiian tropic SPF 4: e = 206.24 M-1cm-1
* Hawaiian tropicSPF 8: e = 389.36 M-1cm-1
* Banana boat SPF 4: e = 285.53 M-1cm-1
* Banana boat SPF 8: e = 238.81 M-1cm-1
* Hawaiian tropic SPF 6: e = 384.51 M-1cm-1
* Hawaiian tropic SPF 6: e = 483.78 M-1cm-1

CALCULATION:
In order to calculate the original concentration of the sunscreen product and 50 mL of ethanol is to divide the mass of sunscreen by the volume of ethanol.
.1138 g =.0023 g/mL
50 mL
The dilution factor of each concentrated solution was measured by the volume of stock solution by the total volume of stock solution and 95% ethanol.
Tube 1: 5.00 = 1
5.00
Tube 2: 3.50 = .7
5.00
Tube 3: 3.00 = .6
5.00
Tube 4: 2.50 = .5
5.00
Tube 5: 2.00 = .4
5.00

Tube 6: .50 = .1
5.00

The volume of each concentrated sunscreen was measured bymultiplying the dilution factor by the original concentration.
Tube 1: 1 x .0023 = .0023 g/mL
Tube 2: .7 x .0023 = .00161 g/mL
Tube 3: .6 x .0023 = .0014 g/mL
Tube 4: .5 x .0023 = .00115 g/mL
Tube 5: .4 x .0023 = .00092 g/mL
Tube 6: .1 x .0023 = .00023 g/mL

The variable E, also known as extinction coefficient was found by making a scatter plot of the data and finding the linear...