Experiment 1: UV Analysis of Sunscreens

consider two different solutions of the same UV absorbing compound. Upon UV analysis, soltuion b gave an absorbance of .8 and solution a gave an absorbance of .4 at the same wavelngth. solution b is higher in concentration than solution a by what ratio

1:2

what range should the solvent used not absorb above

200 nm

at what two absorbances were absorbances recorded

310 - middle of UVB 360 - middle of UVA

what are the max and min wavelength values in UVB

315 and 290 nm

which sunscreens provided the best protection

neutrogena ultradry sheer dry touch with helioplex and

solutions with greatest long wavlength UVA abs

neutrogena with helioplex

UV Vis spectrum is a plot of the

absrbance versus wavelength

oxybenzone

concentration shoulkd be smaller because many other UVB absorbing ingredients

UBV 290-315

delayed more intense suburn; skin cancar, agig, cataracts, immunosuppresion; somewhat absorbed by atm

UV Vis

detects electronic transitions of conjugated pi systems and provides information about the length and structure of the conjugated part of a molecule

NMR

detects transitions between energy states of nuclei; provides infro about the electronic and molecular environment of the nuclei

what is the relationship between absorbance and cocentration

directly proportional when molar abs and path length held constant

the combination of the active ingredients in the sunscreen each absorb different amounts of UVA and UVB rays so it can cause

discrepancies between the concentrations reported and those expected

what are the limitations of beers law

does not accomodate for when multiple ingredients are present in a solution

what determines the amout of energy needed to get an electron to move to a higher energy level

amount of energy in the excited state

what is charactersitic of the structure of common suncreen ingredients

aromatic rings in conjugation with other functional groups

strongest UVA abs ingredient

avobenzone and octocrylene

helioplex

avobenzone and oxybenzone

which compound provided best UVA protection

avobenzone; mutiple conjugated bonds allowed for lower ebergy absorption in the UVA range

what is a key ingredient a sunscreen shuold have to protect against UVA rays

avobenzone; parsol 1789 or Ti)2 or ZnO

butadiene and butene, which has a higher lambda max

butadiene because of multiple conjugated bonds

UVC 100-290

can be lethal but it is almost totally absorbed by ozone in the earth's atmosphere

what is UV used for

extensively used to determine the concentrations of incredibly dilute solutions; relies on beers law

broad absorption band is a result of

fast electron transitions of the molecule in a variety of vibrational energy states

avobenzone

fewer UVA absorbing ingredients so it had a bigger concentration

UVA readily penetrates

glass; UVB does not

sunscreens with what additive provided the best protection

helioplex

higher concentrations have

higher absorbance values

more conjugated bonds

higher lambda max

higher energy is needed to reach

higher orbitals

wavelength on the

horizontal axis

molar abs

how strong light is absorbed at a particular wavelength

molar extinction coefficient

how strongly a sample absorbs light at that wavelength

UVA 315-400 nm

immediate sunburn; penetrates deeply, may cause skin aging; may contribute to skin cancer and aging

isopropyl alcohol safety hazard

irritant

what was the solvent used in this experiment

isopropyl alcohol

when light strikes a molecule

it is absorbed and causes the molecules electrons to jump from a ground state to an excited state

ultraviolet frequencies

shorter wavelengths and larger energies

Uva light is

lower in energy than the other types

Broad spectrum

suncreens with good UVA protection and SPF levels of more than 15

minimal erythemal dose (MED)

the amount of time one can stay out in the sun before getting sunburned

UV visible energies correspond to electronic transitions

the energy needed to excite an electron from one molecular orbital to another

the more conjugated bonds a molecule has

the less energy required to get the electrons to their excited state because the energy differnece is smaller for pi to pi star

the greater the number of conjugated bonds

the lower energy at which the compound will absorb light

lambda max

wavelength of maximum absorbance

why should you put the solution in the cuvette just before you put it in the spectra

will evaporate and give a higher concentration and therefore a higher absorbance

A=ecl

a=absorbance c=concentration l=path length e=molar coefficient

how much did we dilute the already diluted mixture

100 times

relationship between energy an wavelength

E=hv=hc/lambda

a electron is excited from its

HOMO to its LUMO

molar coefficient units

M^-1 CM^-1

lowest energy wave

UVA

ultraviolet light can be divided into

UVA, UVB and UVC

highest energy wave

UVB

what is the only type of UV light that SPF refers to

UVB

sun protective factor

number that indicates the amount of sun protection a product will offer

what were the possible sunscreen ingredients

padiamate O, 2-ethylhexyl salicylate, 2-ethylhexyl p-methoxycinnate, homosalate, octocrylene, oxybenzone, avobenzone, methyl anthranilate, ecamsule

beers law measures concentration of solutions that may be present in

parts per billion

what kind of transition is observed in this experiment

pi to pi star

absorption of energy in the UV and visible regions is caused by

portion of energy beam being absorbed by molecules when electrons in low-energy orbitals are excited into orbitals of higher enegy

UVA can cause

premature aging and possinle DNA damage

how do zinc and titanium provdide protection

provide a physical barrier to reflect both UVA and UVB rays

when molecules have multiple conjugated bonds

this affects how nuch energy is needed to jump from ground to excited state because the orbitals are closer in ebergy

What was the objective of this lab?

to examine the UV absorbing characteristics of a variety of sunscreen preparations; to use results of UV analysis to calculate concentrations of a UV absorbing compound; examine SPF ratings and understand its limitations and uses; to determine what components in sunscreens give better UVA absorption

absorbance is on the

vertical axis

IR spec

vibrations of moleculer bonds to give info on functional groups and nature of bonding

since different spf values were used

want to dilute by the same factor