In this lab, our concept is to find the extinction coefficient “ε” for a specific sunscreen with a sun protection factor (SPF), we are using brand: NO-AD SPF 15 for this experiment, our extension coefficient “ε” value is to be 482.04 cm2/g.
Our objective with this experiment is to find the relation of sun block with the extension coefficient by measuring the absorbent rate of UV rays the sunscreen can absorb. And how it can absorb harmful waves that emit from the sun. Ultra Violet (UV) rays are harmful for the skin if person stays for too long in the sun. It can cause damage to the skin and may lead to cancer.
Also, to relate other sunscreens products to another, as band name price and how well do they do once exposed to the suns UV rays.
As Beer’s Law indicates:
A= (ε) (l) (C)
Where is A is the Absorbance, is proportional to C, the concentration of solution, the higher the concentration the higher the absorbent. ‘A” is also proportional to (l), the length of tube used, the longer the tube, the more molecules in the solution can absorb rays , as they are subjected to more rays. The extinction coefficient (ε), used to calculate the efficiency of absorption, it differs from every compound.
A α C α l α ε
We will be using a 1 cm sample length, and as a sunscreen will be using grams per ml (g/ml)
Please refer to CH221 Laboratory Manual pages 30 – 34
We are using NO-AD SPF 15 sunscreen
Weight= 0.0237 g
And 50 ml of 95% Ethanol
Sunscreen per ml=0.0237/50 = 4.7 x 10-4 g/ml
Making the dilution
mL Stock Sol
mL 95% EtOCH
(g) sunscreen/mL 1
4.7 x 10-4
3.9 x 10-4
3.2 x 10-4
2.6 x 10-4
1.6 x 10-4
7.8 x 10-5
Dilution factor = mL stock Sol/3.00
Tube 1 3.00/3.00=1
Tube 2 2.50/3.00=0.833
Tube 3 2.00/3.00=0.666
Tube 4 1.50/3.00=0.50
Tube 5 1.00/3.00=0.333
Tube 1 0.50/3.00=0.166
(Dilution factor * 4.7 x 10-4 g)
(1*4.7 x 10-4 g = 4.7 x 10-4 g)
(0.833*4.7 x 10-4 g = 3.9 x 10-4 g)
(0.666*4.7 x 10-4 g = 3.2 x 10-4 g)
(0.50*4.7 x 10-4 g = 2.6 x 10-4 g)
(0.333*4.7 x 10-4 g = 1.6 x 10-4 g)
(0.167*4.7 x 10-4 g = 7.8 x 10-5 g)
As per the concentration vs. absorption plot indicates, the slop of the line with equation
y=482.04 x + 0.02
If compared to with the equation
y=482.04 x + 0.02
A= ε l C
And m (slope) = (ε)*(l), and l is 1 cm, then m= ε (extinction coefficient) = 482.04 cm2/g
The absorption rate increased for the concentrated solutions and gradually decreased from tube 1 to tube 6, that means the more particles where intercepting the path of UV rays in the most concentrated solution (tube 1)where A=0.24, and in tube 6(most diluted) the absorption rate was 0.056
And in our wavelength vs. absorbent plot, we see that most of the absorbency occurred when the wave length is around 290nm and 300 nm
That means the concentrated solution with sunscreen absorbed most of the UV rays and energy, therefore blocking it from passing through.
UVA, UVB, UVC are all in the family of Ultra Violet Rays, which are electromagnetic radiation with wavelength shorter than a visible light, because the spectrum starts at a wavelength shorter than wavelength we identify as color. UVA, UVB, UVC are each with a different wavelength.
Type of UV
UVA , long wave, also called black light
400nm – 320 nm
UVB , medium wave
320nm – 280 nm
UVC , shortwave
According to SPF given, it looks like they are consistent, as most of the...
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