USING ENGLISH TO GIVE EVIDANCE.

Chemistry Is Everywhere

Everything you hear, see, smell, taste, and touch involves chemistry and chemicals (matter). And hearing, seeing, tasting, and touching all involve intricate series of chemical reactions and interactions in your body. With such an enormous range of topics, it is essential to know about chemistry at some level to understand the world around us. In more formal terms chemistry is the study of matter and the changes it can undergo. Chemists sometimes refer to matter as ‘stuff’, and indeed so it is. Matter is anything that has mass and occupies space. Which is to say, anything you can touch or hold. Common usage might have us believe that ‘chemicals’ are just those substances in laboratories or something that is not a natural substance. Far from it, chemists believe that everything is made of chemicals. Although there are countless types of matter all around us, this complexity is composed of various combinations of some 100 chemical elements. The names of some of these elements will be familiar to almost everyone. Elements such as hydrogen, chlorine, silver, and copper are part of our everyday knowledge. Far fewer people have heard of selenium or rubidium or hassium. Nevertheless, all matter is composed of various combinations of these basic elements. The wonder of chemistry is that when these basic particles are combined, they make something new and unique. Consider the element sodium. It is a soft, silvery metal. It reacts violently with water, giving off hydrogen gas and enough heat to make the hydrogen explode. Nasty ‘stuff’. Also consider chlorine, a green gas when at room temperature. It is very caustic and choking, and is nasty enough that it was used as a horrible chemical gas weapon in the last century. So what kind of horrible mess is produced when sodium and chlorine are combined? Nothing more than sodium chloride, common table salt. Table salt does not explode in water or choke us; rather, it is a common additive for foods we eat everyday. And so it is with chemistry, understanding the basic properties of matter and learning how to predict and explain how they change when they react to form new substances is what chemistry and chemists are all about. Chemistry is not limited to beakers and laboratories. It is all around us, and the better we know chemistry, the better we know our world.

1. THE ELEMENTS IN THE HUMAN BODY

            Most of the human body is made up of water, H₂O, with cells consisting of 65-90% water by weight. Therefore, it isn't surprising that most of a human body's mass is oxygen. Carbon, the basic unit for organic molecules, comes in second. 99% of the mass of the human body is made up of just six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.

You may also wish to view the element composition of an average human body by mass.

1. Oxygen (65%)
2. Carbon (18%)
3. Hydrogen (10%)
4. Nitrogen (3%)
5. Calcium (1.5%)
6. Phosphorus (1.0%)
7. Potassium (0.35%)
8. Sulfur (0.25%)
9. Sodium (0.15%)
10. Magnesium (0.05%)
11. Copper, Zinc, Selenium, Molybdenum, Fluorine, Chlorine, Iodine, Manganese, Cobalt, Iron (0.70%)
12. Lithium, Strontium, Aluminum, Silicon, Lead, Vanadium, Arsenic, Bromine (trace amounts)

2. A CHEMISTRY OF LOVE

            Scientists haven't developed any magic love potions that you can use to make someone fall in love, but chemistry does play an important role in how a relationship progresses. First, there's attraction. Nonverbal communication plays a big part in initial attraction and some of this communication may involve pheromones, a form of chemical communication. Did you know that raw lust is characterized by high levels of testosterone? The sweaty palms and pounding heart of infatuation are caused by higher than normal levels of norepinepherine. Meanwhile, the 'high' of being in love is due to a rush of phenylethylamine and dopamine. All is not lost once the honeymoon is over. Lasting love confers chemical benefits in the form of stabilized production of serotonin and oxytocin. Can infidelity be blamed on chemistry? Perhaps in part. Researchers have found that suppression of vasopressin can cause males (voles, anyway) to abandon their love nest and seek new mates. Hey, you gotta have chemistry!

3. Why Do Onions Make You Cry?

Unless you've avoided cooking, you've probably cut up an onion and experienced the burning and tearing you get from the vapors it produces. When you cut an onion, you break cells, releasing their contents. A chemical process results, eventually releasing a compound that causes you to tear up when you're slicing and dicing.

ACID EFFECT

Amino acid sulfoxides form sulfenic acids after you slice into an onion. Enzymes that were kept separate are now free to mix with the sulfenic acids to produce propanethiol S-oxide, a volatile sulfur compound that wafts upward toward your eyes. This gas reacts with the water in your tears to form sulfuric acid. The sulfuric acid burns, stimulating your eyes to release more tears to wash the irritant away.

STOP CRYING

There are a few ways to stop the chemical process that causes you to cry when you cut an onion, including:

• Cook the onion. This process inactivates the enzyme, so while the smell of cooked onions may be strong, it doesn't burn your eyes.
• Wear safety goggles or run a fan. This actually prevents the vapors from the compound entering your eyes -- or at least blows the compound's vapors safely away.
• Refrigerate your onion before cutting it. Doing so slows reactions and changes the chemistry inside the onion. You can accomplish the same thing by cutting the onion under water.
• Use stainless steel. The sulfur-containing compounds also leave a characteristic odor on your fingers. You may be able to remove or reduce some of the smell and tears by wiping your fingers on a stainless steel odor eater.

4. How Soap Cleans

Soaps are sodium or potassium fatty acids salts, produced from the hydrolysis of fats in a chemical reaction called saponification. Each soap molecule has a long hydrocarbon chain, sometimes called its 'tail', with a carboxylate 'head'. In water, the sodium or potassium ions float free, leaving a negatively-charged head. Soap is an excellent cleanser because of its ability to act as an emulsifying agent. An emulsifier is capable of dispersing one liquid into another immiscible liquid. This means that while oil (which attracts dirt) doesn't naturally mix with water, soap can suspend oil/dirt in such a way that it can be removed.

The organic part of a natural soap is a negatively-charged, polar molecule. Its hydrophilic (water-loving) carboxylate group (-CO₂) interacts with water molecules via ion-dipole interactions and hydrogen bonding. The hydrophobic (water-fearing) part of a soap molecule, its long, nonpolar hydrocarbon chain, does not interact with water molecules. The hydrocarbon chains are attracted to each other by dispersion forces and cluster together, forming structures called micelles. In these micelles, the carboxylate groups form a negatively-charged spherical surface, with the hydrocarbon chains inside the sphere. Because they are negatively charged, soap micelles repel each other and remain dispersed in water.

Grease and oil are nonpolar and insoluble in water. When soap and soiling oils are mixed, the nonpolar hydrocarbon portion of the micelles break up the nonpolar oil molecules. A different type of micelle then forms, with nonpolar soiling molecules in the center. Thus, grease and oil and the 'dirt' attached to them are caught inside the micelle and can be rinsed away. Although soaps are excellent cleansers, they do have disadvantages. As salts of weak acids, they are converted by mineral acids into free fatty acids:

CH₃(CH₂)₁₆CO₂^-Na⁺ + HCl → CH₃(CH₂)₁₆CO₂H + Na⁺ + Cl^-

These fatty acids are less soluble than the sodium or potassium salts and form a precipitate or soap scum. Because of this, soaps are ineffective in acidic water. Also, soaps form insoluble salts in hard water, such as water containing magnesium, calcium, or iron.

2 CH₃(CH₂)₁₆CO₂^-Na⁺ + Mg²⁺ → [CH₃(CH₂)₁₆CO₂^-]₂Mg²⁺ + 2 Na⁺

The insoluble salts form bathtub rings, leave films that reduce hair luster, and gray/roughen textiles after repeated washings. Synthetic detergents, however, may be soluble in both acidic and alkaline solutions and don't form insoluble precipitates in hard water. But that is a different story...

5. Chemistry of Firework Colors

Creating firework colors is a complex endeavor, requiring considerable art and application of physical science. Excluding propellants or special effects, the points of light ejected from fireworks, termed 'stars', generally require an oxygen-producer, fuel, binder (to keep everything where it needs to be), and color producer. There are two main mechanisms of color production in fireworks, incandescence and luminescence.

 INCANDESCENCE

Incandescence is light produced from heat. Heat causes a substance to become hot and glow, initially emitting infrared, then red, orange, yellow, and white light as it becomes increasingly hotter. When the temperature of a firework is controlled, the glow of components, such as charcoal, can be manipulated to be the desired color (temperature) at the proper time. Metals, such as aluminum, magnesium, and titanium, burn very brightly and are useful for increasing the temperature of the firework.

LUMINESCENCE

Luminescence is light produced using energy sources other than heat. Sometimes luminescence is called 'cold light', because it can occur at room temperature and cooler temperatures. To produce luminescence, energy is absorbed by an electron of an atom or molecule, causing it to become excited, but unstable. The energy is supplied by the heat of the burning firework. When the electron returns to a lower energy state the energy is released in the form of a photon (light). The energy of the photon determines its wavelength or color. In some cases, the salts needed to produce the desired color are unstable. Barium chloride (green) is unstable at room temperatures, so barium must be combined with a more stable compound (e.g., chlorinated rubber). In this case, the chlorine is released in the heat of the burning of the pyrotechnic composition, to then form barium chloride and produce the green color. Copper chloride (blue), on the other hand, is unstable at high temperatures, so the firework cannot get too hot, yet must be bright enough to be seen.

QUALITY OF FIREWORK INGREDIENTS

Pure colors require pure ingredients. Even trace amounts of sodium impurities (yellow-orange) are sufficient to overpower or alter other colors. Careful formulation is required so that too much smoke or residue doesn't mask the color. With fireworks, as with other things, cost often relates to quality. Skill of the manufacturer and date the firework was produced greatly affect the final display (or lack thereof).

TABLE OF FIREWORK COLORANTS

Color	Compound
Red	strontium salts, lithium salts lithium carbonate, Li2CO3 = red strontium carbonate, SrCO3 = bright red
Orange	calcium salts calcium chloride, CaCl2 calcium sulfate, CaSO4·xH2O, where x = 0,2,3,5
Gold	incandescence of iron (with carbon), charcoal, or lampblack
Yellow	sodium compounds sodium nitrate, NaNO3 cryolite, Na3AlF6
Electric White	white-hot metal, such as magnesium or aluminum barium oxide, BaO
Green	barium compounds + chlorine producer barium chloride, BaCl+ = bright green
Blue	copper compounds + chlorine producer copper acetoarsenite (Paris Green), Cu3As2O3Cu(C2H3O2)2 = blue copper (I) chloride, CuCl = turquoise blue
Purple	mixture of strontium (red) and copper (blue) compounds
Silver	burning aluminum, titanium, or magnesium powder or flakes

SEQUENCE OF EVENTS

Just packing colorant chemicals into an explosive charge would produce an unsatisfying firework! There's a sequence of events leading to a beautiful, colorful display. Lighting the fuse ignites the lift charge, which propels the firework into the sky. The lift charge can be black powder or one of the modern propellants. This charge burns in a confined space, pushing itself upward as hot gas is forced through a narrow opening. The fuse continues to burn on a time delay to reach the interior of the shell. The shell is packed with stars that contain packets of metal salts and combustible material. When the fuse reaches the star, the firework is high above the crowd. The star blows apart, forming glowing colors through a combination of incandescent heat and emission luminescence.