Chemistry of Everyday Life.
Chemistry is everywhere. The air we breathe, the ground we stand on, the seas we sail, and the variety of living things including our own bodies--all these are made of substances that we call chemicals. These chemicals interact with one another, and, in many cases, these interactions produce new substances through processes known as chemical reactions.
Over time, we have learned much about chemicals and have mastered numerous chemical reactions, giving us the ability to modify existing substances and synthesize new ones. Consequently, we have created a whole new realm of materials such as those used in paints, plastics, textiles, pharmaceuticals, soaps, cosmetics, and more. Thus chemistry has provided an important foundation for our modern technological world.
In what ways do we observe the operation of chemical principles in our everyday lives? Let us consider a few examples that help illustrate our connections to chemistry.
Food and drink
In your morning haste, you may have tried to hard-boil eggs rapidly and found that some eggshells crack in the process. Why does that happen? The reason is linked to the presence of an air pocket at one end of each egg, just beneath the shell. When an egg is heated, its air pocket expands. If the water is boiled too fast, the expanded air does not have time to diffuse through the porous shell, causing the shell to crack. To prevent this, experienced cooks recommend heating an egg slowly, starting with cold water.
If you boil an egg for too long, you may observe that the surface of the yolk acquires a gray-green coloration. This color is a consequence of a reaction that produces a harmless compound named ferrous sulfide (or iron(II) sulfide). An egg contains both iron and protein. Prolonged heating of an egg at a high temperature causes the sulfur-containing amino acids in its proteins to decompose and generate hydrogen sulfide. The iron in the yolk reacts with the hydrogen sulfide to produce green ferrous sulfide.
Rapid boiling can also cause the pot of water to overflow; when the water comes in contact with gas from the burner, the flame turns yellow. This phenomenon indicates that the water contains sodium ions Yellow light is produced by heating sodium atoms, which come from salt (sodium chloride) that is naturally dissolved in water. The white residue on the gas burner is further proof of the presence of the salt.
In 1911, the Morton Salt Company launched the image of a girl with an umbrella walking in a rain shower while pouring salt behind her, with the accompanying slogan, "When It Rains It Pours." The implication was that the table salt produced by the company could be poured easily even in humid conditions. The salt contained an anticaking agent--an ingredient that absorbs many times its weight in water without itself dissolving, keeping the salt dry and flowing freely. At first, the anticaking agent used was magnesium carbonate; today it is calcium silicate.
Those of us who have baked bread, cakes, and muffins are aware that for the dough or batter to rise, it needs to contain a leavening agent, such as baking soda or baking powder. How do leavening agents exert their effect? Baking soda is another name for sodium bicarbonate. Usually, a recipe that calls for baking soda also includes an acidic ingredient, such as buttermilk or yogurt, that reacts with the sodium bicarbonate (a base) to produce bubbles of carbon dioxide gas. Likewise, baking powder, which includes baking soda and an acid (such as cream of tartar), reacts in the presence of moisture and heat to produce carbon dioxide. The bubbles of gas that are trapped in the dough cause it to rise.
A leavening effect can also be achieved by trapping air in the batter through vigorous beating, called air leavening, used in making sponge cakes; or by vaporizing water, known as steam leavening, used in producing the cavities in cream puffs and eclairs.
Baking soda is additionally useful as a handy fire extinguisher for small fires. In the high temperatures typical of fires, it decomposes to produce carbon dioxide gas. This gas, which does not burn, is denser than air and displaces air. As a result, the fire is deprived of oxygen and is extinguished.
The manufacture of soft drinks is also rich in chemistry, such as in the use of ingredients that produce special colors and flavors. One type of sweetener used in diet sodas is sucralose, which is made from sucrose (table sugar) and is advertised as containing "no calories." Given that regular sugar provides calories (or energy) when metabolized by the body, how can sucralose have zero caloric value? The reason is that sucralose remains undigested as it passes through the body, therefore adding no calories [see "How Sweet It Is!" in The World & I, February 2000, p. 172].
How do sutures on a wound stay in place long enough to promote healing and then disappear mysteriously? Today's surgeons use sutures made of synthetic, biodegradable polymers that ensure biocompatibility, tensile strength, and dissolution by the body's natural action. Some of these polymers degrade by reacting with water, others by reacting with an enzyme in the body. The degradation products are carbon dioxide and water, which are produced in minute quantities that do not affect the body.
Then there is the mystery of how a "timed-release" oral medication, when ingested, controls the release of its active ingredients over a specified time interval. The secret to producing this effect lies in the coating that encapsulates the medication. The coating is made from a water-soluble polymer; the thicker it is, the longer it takes to dissolve in the body's fluids. For instance, the decongestant Contac consists of medicine that is enclosed in a polymer in the shape of tiny beads or larger caplets. For a "12-hour" remedy, the coating thickness is carefully designed to release the medicine gradually over a 12-hour period.
If you've taken Alka-Seltzer or Bromo-Seltzer to treat acid indigestion, you are undoubtedly familiar with the effervescence produced when tablets of these antacids are added to water. What causes the fizz? Each tablet contains baking soda and citric acid, which react with each other in solution to produce carbonic acid. The carbonic acid quickly decomposes to generate water and bubbles of carbon dioxide.
Why are cyanide-containing substances extremely poisonous? Cyanide has a strong affinity for certain metals such as iron. If ingested, it binds quickly and strongly to the iron in enzymes that are important for cell respiration. This interaction impairs cell respiration, which in turn causes normal cell functions to cease. Antidotes for cyanide poisoning contain a different metal, such as cobalt (in the form of cobalt salts). The cyanide forms an even more stable complex with cobalt, leaving the iron free to function properly.
Each time you reach for hydrogen peroxide from your medicine cabinet, you probably wonder why it is stored in a dark plastic bottle. Over time, hydrogen peroxide decomposes into water and oxygen--a process that is accelerated by heat, light, or trace amounts of metals. To slow this decomposition, a dark brown container limits the wavelengths of light that can be absorbed by the solution. In addition, a plastic bottle is preferred over a glass one because glass contains trace amounts of metal ions.
Chemistry of cleaning
Household cleansers containing bleach or ammonia are quite useful as disinfectants, deodorizers, and stain removers. But the chemistry of these products dictates that you never mix bleach with ammonia cleansers. Mixing them leads to the formation of toxic gases called chloramines, characterized by acrid fumes that can burn mucous membranes. Scented bleaches can mask our natural ability to detect these harmful fumes.
Speaking of ammonia cleansers, how do they remove certain floor waxes? Modern floor finishes often consist of polymers blended to provide such qualities as durability and gloss retention. The polymer chains (which are long molecules) are cross-linked to form a strong, three-dimensional lattice. In some cases, the cross-linking is achieved with the use of metal ions. Ammonia cleansers can dissolve these metal ions, thereby destroying the lattice structure and allowing the wax to be removed.
If you wish to clean tarnished brass or copper items, try using some common foods in your kitchen: vinegar, lemon juice, or ketchup. As you may know, copper is a metal, and brass is a mixture of copper and zinc. Their surfaces are tarnished on prolonged exposure to air--especially in the presence of moisture and high concentrations of carbon dioxide or sulfur dioxide--to form compounds that range in color from black to blue to dark green. These compounds dissolve in acidic solutions such as the acetic acid present in vinegar, citric acid in lemon juice, and ascorbic acid (vitamin C) in tomato ketchup.
For a similar reason, vinegar is recommended for removing white deposits that develop on such items as automatic coffeemakers, steam irons, dishwashers, teapots, faucet heads, and showerheads. These deposits come from what is called hard water--that is, water that contains high concentrations of calcium and magnesium ions. As water travels through the ground, it accumulates calcium and magnesium ions from minerals such as limestone and dolomite. These ions may then combine with carbon dioxide that is dissolved in the water to form calcium and magnesium carbonates, which are white solids. Vinegar dissolves these solids.
Hard water has also been associated with scum on the bathtub or laundry. The waxy scum arises when calcium and magnesium ions in the water combine with certain ingredients of soaps and detergents, such as fatty acid ions and phosphates, to form insoluble substances. A number of water-softening products--such as Calgon, White Rain, and Spring Rain--contain "sequestering agents" that complex with the calcium and magnesium ions, preventing them from interacting with the soaps and detergents.
You have probably also experienced the clogging of drainpipes. This problem is often caused by the buildup of greases, soaps, and detergents along the inner walls of the pipes. To unclog the drain, you may use a product such as Drano or Liquid-Plumr. These products contain caustic substances that, when dissolved in water, produce highly alkaline solutions; these in turn can effectively dissolve grease. Some crystal drain cleaners also contain solid aluminum particles that react with an alkaline solution to produce hydrogen gas and heat. The agitation of the evolving gas and the heat released generate additional forces to open up drains.
When it comes time to clean the furniture, remember that dust particles carry an electrical charge and are attracted to any surface that develops a charge. If you simply wipe the furniture, the dust will come off temporarily, but the friction of rubbing enhances the static electrical charge on the surface, making it more likely to attract dust. For this reason, furniture makers discourage dusting without polish. Furniture polishes contain substances, such as silicone oil and lemon oil, that are not prone to develop static charges and therefore do not attract dust.
Lightbulbs, etched glass, and more
Have you ever examined a burned-out lightbulb and wondered why there is a dark spot on the glass? An incandescent lightbulb has a tungsten filament that is heated to produce white light. When the bulb is being used, minute quantities of the tungsten undergo sublimation--a process of conversion from the solid state to the vapor state. The tungsten vapors become deposited on the inner surface of the bulb, and the deposit builds up gradually to produce a dark spot.
Speaking of lightbulbs, how is a frosted lightbulb produced? The inner surface of the glass bulb is treated with hydrofluoric acid, which reacts with the glass and produces a white substance that coats the surface. The frosted surface dissipates the light, softening the glare of an unconcealed filament.
Hydrofluoric acid is also used to produce decorative designs on etched glass. In one approach, the glass surface is first coated with layers of paraffin or beeswax, and metal needles are used to create patterns through the coating. The glass (with the coating) is then dipped in a solution of hydrofluoric acid, which etches the design on the unprotected areas of the surface.
Another fascinating subject is disappearing ink. How does a message written in seemingly standard ink disappear from sight? One strategy involves using an acid-base indicator such as thymolphthalein, which has a deep blue color in an alkaline solution but is colorless in acidic conditions. Thus, a blue "ink" can be prepared by dissolving thymolphthalein in a solution made alkaline with sodium hydroxide. If you write with this ink and let it dry, the color gradually disappears. What happens is that carbon dioxide in the air combines with sodium hydroxide in the ink to form sodium carbonate, which is less basic. In addition, carbon dioxide combines with water in the ink to produce carbonic acid. The indicator responds to the acid and turns colorless.
The amazing ability of "superglues" to provide strong, rapid adhesion for a wide variety of surfaces is also based on chemical principles. The glue generally contains a substance that is classified as an alkyl cyanoacrylate monomer. In the presence of water, this substance is rapidly converted into a three-dimensional, cross-linked polymer that has many attractive interactions with the surfaces that are bonded together. In addition, water enhances the adhesive interactions of the polymer with the surfaces. Superglues stick to different types of materials because most surfaces have a film of moisture derived from typical atmospheric conditions.
An entirely different group of polymers, known as aramids, are particularly useful for the manufacture of bulletproof vests, firefighters' jackets, protective helmets, cut-resistant gloves, puncture-resistant tires, canoes, kayaks, and various types of sporting equipment. These polymers exhibit such features as ultrahigh strength, rigidity, flame resistance, and inertness to chemical attack. One example of aramid polymers is Kevlar, developed by DuPont in 1971. It is made from two types of building blocks--a diamine and a diacid--that are joined together to form long, rodlike chains. These chains are linked through an extensive network of interactions, giving the material greater stability and rigidity. Based on this structure, the strength per unit weight of Kevlar is five times that of steel.
The above examples barely scratch the surface of the world of chemistry. Nonetheless, the next time you prepare food, take a medication, clean your home, or admire a glass etching, think of how chemicals and chemical principles are an integral part of our day-to-day existence.n
Kerry K. Karukstis and Gerald R. Van Hecke are professors in the Department of Chemistry at Harvey Mudd College in Claremont, California. This article is based on their book Chemistry Connections: The Chemical Basis of Everyday Phenomena, second edition (Academic Press, 2003).
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|Author:||Karukstis, Kerry K.; Van Hecke, Gerald R.|
|Publication:||World and I|
|Date:||Nov 1, 2003|
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