shiping_upsi

Monday, October 25, 2010

How Does Sunscreen Work?

Sunscreen combines organic and inorganic chemicals to filter the light from the sun so that less of it reaches the deeper layers of your skin. Like a screen door, some light penetrates, but not as much as if the door wasn't present. Sunblock, on the other hand, reflects or scatters the light away so that it doesn't reach the skin at all.

The reflective particles in sunblocks usually consist of zinc oxide or titanium oxide. In the past, you could tell who was using a sunblock just by looking, because the sunblock whited out the skin. Not all modern sunblocks are visible because the oxide particles are smaller, though you can still find the traditional white zinc oxide. Sunscreens usually include sunblocks as part of their active ingredients.

What Sunscreens Screen

The portion of the sunlight that is filtered or blocked is ultraviolet radiation. There are three regions of ultraviolet light.

UV-A penetrates deeply into the skin and can lead to cancer and premature skin aging.
UV-B is involved in tanning and burning of your skin.
UV-C is completely absorbed by the earth's atmosphere.

The organic molecules in sunscreen absorb the ultraviolet radiation and release it as heat.

PABA (para-aminobenzoic acid) absorbs UVB
Cinnamates absorb UVB
Benzophenones absorb UVA
Anthranilates absorb UVA and UVB
Ecamsules absorb UVA

What SPF Means

SPF stands for Sun Protection Factor. It's a number that you can use to help determine how long you can stay in the sun before getting a sunburn. Since sunburns are caused by UV-B radiation, SPF does not indicate protection from UV-A, which can cause cancer and premature aging of the skin.

Your skin has a natural SPF, partially determined by how much melanin you have, or how darkly pigmented your skin is. The SPF is a multiplication factor. If you can stay out in the sun 15 minutes before burning, using a sunscreen with an SPF of 10 would allow you to resist the burn for 10x longer or 150 minutes.

Although the SPF only applies to UV-B, the labels of most products indicate if they offer broad spectrum protection, which is some indication of whether or not they work against UV-A radiation. The particles in sunblock reflect both UV-A and UV-B

How Fireworks Work Firecrackers, Sparklers & Aerial Shell Fireworks

Fireworks have been a traditional part of New Year's celebrations since they were invented by the Chinese almost a thousand years ago. Today fireworks displays are seen on most holidays. Have you ever wondered how they work? There are different types of fireworks. Firecrackers, sparklers, and aerial shells are all examples of fireworks. Though they share some common characteristics, each type works a little differently. Firecrackers

Firecrackers are the original fireworks. In their simplest form, firecrackers consists of gunpowder wrapped in paper, with a fuse. Gunpowder consists of 75% potassium nitrate (KNO₃), 15% charcoal (carbon) or sugar, and 10% sulfur. The materials will react with each other when enough heat is applied. Lighting the fuse supplies the heat to light a firecracker. The charcoal or sugar is the fuel. Potassium nitrate is the oxidizer, and sulfur moderates the reaction. Carbon (from the charcoal or sugar) plus oxygen (from the air and the potassium nitrate) forms carbon dioxide and energy. Potassium nitrate, sulfur, and carbon react to form nitrogen and carbon dioxide gases and potassium sulfide. The pressure from the expanding nitrogen and carbon dioxide explode the paper wrapper of a firecracker. The loud bang is the pop of the wrapper being blown apart.

Sparklers

A sparkler consists of a chemical mixture that is molded onto a rigid stick or wire. These chemicals often are mixed with water to form a slurry that can be coated on a wire (by dipping) or poured into a tube. Once the mixture dries, you have a sparkler. Aluminum, iron, steel, zinc or magnesium dust or flakes may be used to create the bright, shimmering sparks. An example of a simple sparkler recipe consists of potassium perchlorate and dextrin, mixed with water to coat a stick, then dipped in aluminum flakes. The metal flakes heat up until they are incandescent and shine brightly or, at a high enough temperature, actually burn. A variety of chemicals can be added to create colors. The fuel and oxidizer are proportioned, along with the other chemicals, so that the sparkler burns slowly rather than exploding like a firecracker. Once one end of the sparkler is ignited, it burns progressively to the other end. In theory, the end of the stick or wire is suitable to support it while burning.

Rockets & Aerial Shells

When most people think of 'fireworks' an aerial shell probably comes to mind. These are the fireworks that are shot into the sky to explode. Some modern fireworks are launched using compressed air as a propellent and exploded using an electronic timer, but most aerial shells remain launched and exploded using gunpowder. Gunpowder-based aerial shells essentially function like two-stage rockets. The first stage of an aerial shell is a tube containing gunpowder, that is lit with a fuse much like a large firecracker. The difference is that the gunpowder is used to propel the firework into the air rather than explode the tube. There is a hole at the bottom of the firework so the expanding nitrogen and carbon dioxide gases launch the firework into the sky. The second stage of the aerial shell is a package of gunpowder, more oxidizer, and colorants. The packing of the components determines the shape of the firework.

Sparklers are a type of firework that produces a shower of glittery sparks, but does not explode.

Hair Color Chemistry Haircoloring: Bleaching & Dyeing

The first safe commercial haircolor was created in 1909 by French chemist Eugene Schuller, using the chemical paraphenylenediamine. Hair coloring is very popular today, with over 75% of women coloring their hair and a growing percentage of men following suit. How does haircolor work? It's the result of a series of chemical reactions between the molecules in hair, pigments, as well as peroxide and ammonia, if present.

What is Hair?

Hair is mainly keratin, the same protein found in skin and fingernails. The natural color of hair depends on the ratio and quantities of two other proteins, eumelanin and phaeomelanin. Eumelanin is responsible for brown to black hair shades while phaeomelanin is responsible for golden blond, ginger, and red colors. The absence of either type of melanin produces white/gray hair.

Natural Colorants

People have been coloring their hair for thousands of years using plants and minerals. Some of these natural agents contain pigments (e.g., henna, black walnut shells) and others contain natural bleaching agents or cause reactions that change the color of hair (e.g., vinegar). Natural pigments generally work by coating the hair shaft with color. Some natural colorants last through several shampoos, but they aren't necessarily safer or more gentle than modern formulations. It's difficult to get consistent results using natural colorants, plus some people are allergic to the ingredients.

Temporary Hair Color

Temporary or semi-permanent haircolors may deposit acidic dyes onto the outside of the hair shaft or may consist of small pigment molecules that can slip inside the hair shaft, using a small amount of peroxide or none at all. In some cases, a collection of several colorant molecules enter the hair to form a larger complex inside the hair shaft. Shampooing will eventually dislodge temporary hair color. These products don't contain ammonia, meaning the hair shaft isn't opened up during processing and the hair's natural color is retained once the product washes out.

How Lightening Works

Bleach is used to lighten hair. The bleach reacts with the melanin in hair, removing the color in an irreversible chemical reaction. The bleach oxidizes the melanin molecule. The melanin is still present, but the oxidized molecule is colorless. However, bleached hair tends to have a pale yellow tint. The yellow color is the natural color of keratin, the structural protein in hair. Also, bleach reacts more readily with the dark eumelanin pigment than with the phaeomelanin, so some gold or red residual color may remain after lightening. Hydrogen peroxide is one of the most common lightening agents. The peroxide is used in an alkaline solution, which opens the hair shaft to allow the peroxide to react with the melanin.

Permanent Hair Color

The outer layer of the hair shaft, its cuticle, must be opened before permanent color can be deposited into the hair. Once the cuticle is open, the dye reacts with the inner portion of the hair, the cortex, to deposit or remove the color. Most permanent hair colors use a two-step process (usually occurring simultaneously) which first removes the original color of the hair and then deposits a new color. It's essentially the same process as lightening, except a colorant is then bonded within the hair shaft. Ammonia is the alkaline chemical that opens the cuticle and allows the hair color to penetrate the cortex of the hair. It also acts as a catalyst when the permanent hair color comes together with the peroxide. Peroxide is used as the developer or oxidizing agent. The developer removes pre-existing color. Peroxide breaks chemical bonds in hair, releasing sulfur, which accounts for the characteristic odor of haircolor. As the melanin is decolorized, a new permanent color is bonded to the hair cortex. Various types of alcohols and conditioners may also be present in hair color. The conditioners close the cuticle after coloring to seal in and protect the new color.

Periodic Table Elements in Fireworks

Periodic Table
Elements in Fireworks

Fireworks rely on the chemical characteristics of the elements that are used to make them. This special periodic table highlights the elements that have significance to fireworks and pyrotechnics. Click on the element to see what it does.

1
H

2
He

3
Li

4
Be

5
B

6
C

7
N

8
O

9
F

10
Ne

11
Na

12
Mg

13
Al

14
Si

15
P

16
S

17
Cl

18
Ar

19
K

20
Ca

21
Sc

22
Ti

23
V

24
Cr

25
Mn

26
Fe

27
Co

28
Ni

29
Cu

30
Zn

31
Ga

32
Ge

33
As

34
Se

35
Br

36
Kr

37
Rb

38
Sr

39
Y

40
Zr

41
Nb

42
Mo

43
Tc

44
Ru

45
Rh

46
Pd

47
Ag

48
Cd

49
In

50
Sn

51
Sb

52
Te

53
I

54
Xe

55
Cs

56
Ba

57
La

72
Hf

73
Ta

74
W

75
Re

76
Os

77
Ir

78
Pt

79
Au

80
Hg

81
Tl

82
Pb

83
Bi

84
Po

85
At

86
Rn

87
Fr

88
Ra

89
Ac

104
Rf

105
Db

106
Sg

107
Bh

108
Hs

109
Mt

110
110

111
111

112
112

More Information

Chemistry of Firework Colors

History of Fireworks

How Fireworks Work

How Do Sparklers Work?

Fireworks & Pyrotechnics Index

How to Make Black Powder

'Normal' Periodic Table

Toxic Chemicals in Cosmetics Hazardous Chemicals in Cosmetics and Personal Care Product

Some of the ingredients in cosmetics and personal care products are chemicals that may be hazardous to your health. Take a look at some of the ingredients to watch for and the health concerns raised by these chemicals.

antibacterials

This is the two-dimensional chemical structure of the antibacterial and antifungal agent triclosan.

Harbin, public domain

Antibacterials (e.g., Triclosan) are found in many products, such as hand soaps, deodorants, toothpastes and body washes.

Health Hazards: Some antibacterial agents are absorbed through the skin. Triclosan has been shown to be secreted in breast milk. These chemicals may be toxic or carcinogenic. One study has found antibacterials may interfere with the functioning of testosterone in cells. Antibacterials can kill the 'good' protective bacteria as well as pathogens, actually increasing susceptibility to infection. The products may increase the rate of development of resistant strains of bacteria.

butyl acetate

Butyl acetate is found in nail strengtheners and nail polishes.

Health Hazards: Butyl acetate vapors may cause dizziness or drowsiness. Continued use of a product containing butyl acetate may cause skin to crack and become dry.

butylated hydroxytoluene

Butylated hydroxytoluene is found in a variety of cosmetics and personal care products. It is an antioxidant which helps slow the rate at which a product changes color over time.

Health Hazards: Butylated hydroxytoluene may cause skin and eye irritation.

coal tar

Coal tar is used to control itching and scaling, to soften skin, and as a colorant.

Health Hazards: Coal tar is a human carcinogen.

diethanolamine (DEA)

This is the two-dimensional chemical structure of diethanolamine or DEA.

Edgar181, public domain

Diethanolamine is a contaminant associated with cocamide DEA and lauramide DEA, which are used as emulsifiers and foaming agents in products such as shampoos, shaving creams, moisturizers, and baby washes.

Health Hazards: DEA can be absorbed into the body through the skin. It can act as a carcinogen and can be converted to nitrosamine, which is also carcinogenic. DEA is a hormone disruptor and robs the body of choline needed for fetal brain development.

1,4-dioxane

This is a contaminant that may be associated with sodium laureth sulfate, PEG, and most ethoxylated ingredients with names ending in -eth. These ingredients are found in many products, most notably shampoos and body washes.

1,4 dioxane is known to cause cancer in animals and has a high probability of carcinogenicity in humans.

formaldehyde

Ben Mills

Formaldehyde is used as a disinfectant and preservative in a variety of products, such as nail polish, soap, deodorant, shaving cream, eyelash adhesive and shampoo. Even when it isn't listed as an ingredient, it can result from the breakdown of other ingredients, most notably diazolidinyl urea, imidazolidinyl urea and quaternium compounds.

Health Hazards: The European Union has banned the use of formaldehyde in cosmetics and personal care products. It is associated with multiple health concerns, such as respiratory tract and eye irritation, cancer, immune system damage, genetic damage, and triggering asthma.

fragrance

jesus-is-lord, morguefile.com

The catch-all name "fragrance" may be used to indicate any of a number of chemicals in a personal care product.

Health Hazards: Many fragrances are toxic. Some of these fragrances may be phthalates, which can act as obesogens (cause obesity) and may otherwise disrupt normal endocrine function, including reproductive health. Phthalates may cause developmental defects and delays.

lead

Dormroomchemist, wikipedia.com

Lead typically occurs as a contaminant, such as in hydrated silica, an ingredient in toothpaste. Lead acetate is added as an ingredient in some lipsticks and men's hair dye.

Health Hazards: Lead is a neurotoxin. It can cause brain damage and developmental delays even at extremely low concentrations.

mercury

Femto/Elementbox04, wikipedia.org

The FDA permits the use of mercury compounds in eye makeup at concentrations up to 65 parts per million. The preservative thimerosol, found in some mascaras, is a mercury-containing product.

Health Hazards: Mercury is associated with a host of health concerns including allergic reactions, skin irritation, toxicity, neurological damage, bioacculumation, and environmental damage. Mercury readily passes into the body through the skin, so normal use of the product results in exposure.

talc

Talc is used to absorb moisture and provide a hint of sparkle. It is found in eye shadow, blush, baby powder, deodorant and soap.

Talc is known to act as a human carcinogen and has been directly linked to ovarian cancer. Talc can act similarly to asbestos when inhaled and may lead to the formation of lung tumors.

toluene

NEUROtiker, public domain

Toluene is found in nail polish and hair dye as a solvent, to improve adhesion, and to add gloss.

Health Hazard: Toluene is toxic. It is associated with reproductive and developmental damage. Toluene may be carcinogenic. In addition to decreasing fertility, toluene may cause liver and kidney damage.

Health and Beauty Chemistry

Make Cosmetics & Personal Care Products

Make Your Own Products

Elements in the Human Body

Find out what elements are in the human body and what these elements do.

99% of the mass of the human body is made up of only six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus. Every organic molecule contains carbon. Since 65-90% of each body cell consists of water (by weight), it isn't surprising that oxygen and hydrogen are major components of the body.Here's is a look at the major elements in the body and what these elements do.

Images 1-11 of 11

Enter Gallery

Oxygen	Carbon	Hydrogen	Nitrogen
Calcium	Phosphorus	Potassium	Sodium
Chlorine	Magnesium	Sulfur

Resources of Chemistry Topics

Chemistry Topics

(adapted from "Chemistry Cassettes")

These learning resources are designed for individual, self-paced learning and are appropriate for post-16 students in schools, colleges and universities.

They were originally created as cassettes and booklets by the Educational Techniques Group of the RSC - hence the original name "Chemistry Cassettes". They are now available for personal private study in MP3 and PDF format.

How to use the workbooks and audio

Instructions and suggestions

Software Requirements

MP3 files can played on many different types of software.

Copyright