Why Is Milk White? (2 page)

I was talking one day with my coauthor, 11-year-old Alexa Coelho, about science, in particular about chemistry, which is her favorite subject. I was explaining that in much of science, the hard part is coming up with the right questions. Once you ask the right questions, half the work is done.

She had been reading a book that had two authors. One was a person with a special story to tell, and the other was a person who had written several books and knew how to put the right words onto paper to tell the story well. Alexa thought it might be fun to write a book but thought she would need some assistance from someone who knew the ins and outs of the publishing business. I agreed to help her in her endeavors.

Alexa then took the reins and worked very hard, without any assistance, doing the hard part of science. She spent almost all of her free time coming up with page after page of questions about chemistry that she wished she knew the answers to.

When she had come up with an astounding 200 questions about chemistry, she made me a gracious and generous offer. She would split the profits from her book 50/50 with me, if I would do the easy part and write the answers to the questions. I accepted her kind offer, and the result is this book.

Along with the addition of a few fun projects and a glossary, the questions got trimmed a bit, as happens during editing. But Alexa assures me that all of the important ones are still there.

How to Read
Structural Formulas

Throughout this book, you'll see drawings that illustrate a particular chemical's
structural formula
âhow it's shaped at a molecular level. Knowing its shape is often quite useful in understanding how it behaves and how it interacts with other compounds.

Chemists use a few simplifying rules to show how a molecule is shaped without cluttering up the picture. Most of the atoms that make up a molecule are labeled; in the structural formula above, hydrogen is labeled with an “H” and oxygen is labeled with an “O.” But carbon atoms are so common that they are not labeled with a “C.” Instead, they are assumed to be anywhere on a formula where two lines join, like the two middle bends in the above drawing.

And since hydrogens attached to carbons are also very common, and carbon always has four bonds, any place on a formula where fewer than four lines join, it is assumed that hydrogens fill
the carbon's remaining bonds, and so they are not labeled either. That means that there are two more hydrogen atoms attached to each of the unlabeled carbons at the center of the formula on the previous page.

People and
Animals

Though Alexa's questions are about her favorite subject, chemistry, it turns out that a lot of chemistry is involved in how people and animals react to their environment and how they grow, eat, and breathe.

Can chemicals cause mutations in animals?

Yes. But they won't turn you into Spider-Man.

Chemicals that cause mutations are called
mutagens.
Mutagens cause changes in the DNA in the cells of an organism. DNA is a code that spells out how to make things in a cell. The code is made up of letters like an alphabet. Each letter represents a different chemical, called a
nucleotide.
There are four letters in the DNA alphabet: A, C, G, and T.

But there are some molecules that look like one of the molecules DNA uses for letters in the code. When the cell makes new DNA, it might use one of the molecules that looks like a T (for example), so that instead of spelling ACTGGTACCT, the DNA spells ACXGGTACCT. That X is the new molecule.

Usually when a spelling error like this occurs, the cell detects it and throws that DNA away so nothing bad happens. But sometimes the molecule looks so much like the real-letter molecule that it goes undetected. The misspelled word usually just doesn't work, so the cell doesn't make the chemical (usually a protein) it was supposed to make.

If the missing chemical is important, the cell might die, and that would be the end of it. If the missing chemical was not so important, such as something that made hair dark, you might get a gray hair instead. If the cell was a fertilized egg, all the hairs in the new animal might be white, and you get an
albino,
an animal that lacks the dark colors that make suntans and dark hair.

Sometimes the spelling change does make a protein, but the protein is just slightly different. It might not work as well, or it might work differently, maybe making a different color, and you get a blue frog instead of a green one.

Other chemicals might change a C into a T. Or break DNA into pieces that get put back together in the wrong order, or with a piece missing, or an extra piece added.

The likelihood of a mutation being beneficial is very small. A cell is a complicated piece of machinery, and making random changes would be like making a random change to a car engine by hitting it with a rock. The engine is unlikely to work better afterward. But occasionally a change makes the organism work better. This is evolution.

What happens if you breathe in smoke or carbon dioxide?

Smoke is made up of carbon dioxide, carbon monoxide, water vapor, soot, and smaller amounts of many other molecules and bits of ash. Soot and ash are filtered by your nose and pushed out of your throat when you cough. Carbon monoxide is toxic because it binds to blood cells instead of oxygen and doesn't let go, so your cells can't get any oxygen to breathe.

Carbon dioxide is something we breathe all the time, since it is a part of the air we breathe out of our lungs. Our bodies sense how much carbon dioxide is in our blood, and when the levels rise, we feel the need to take a breath.

If you breathe in too much carbon dioxide, your blood becomes acidic, since carbon dioxide dissolves in water to form carbonic acid. After breathing too much carbon dioxide, your body adjusts by making you breathe faster, so you exhale more carbon dioxide. It is the buildup of too much carbon dioxide that makes you feel the intense need to breathe when you are holding your breath or swimming underwater.

What does biology have to do with chemistry?

Biological organisms are made of chemicals. Some branches of biology study how the chemicals in organisms do their jobs. The scientists who study the molecules of life are called
biochemists.

There are many biologists who study aspects of living things that are not directly related to the molecules that make up the animal or plant. But since animals and plants are made up of molecules, even people who study animal behavior or classify plants will eventually find some chemistry is useful.

Suppose you were studying the behavior of butterflies. You might want to know how they find their food or how they find their mates. Both of these behaviors involve sensing molecules in the air using their antennae. That's chemistry.

Or maybe you want to study human nutrition. To understand why some foods are essential, you might want to learn about vitamins, minerals, proteins, fats, carbohydrates, and other chemicals that make up our food.

Charles Darwin studied biology and came up with the theory of evolution. But it was chemists who figured out how evolution works, many years after Darwin was no longer around.

Doctors used to give their patients mixtures of plant material or other things in attempts to cure or alleviate symptoms of disease. But it was chemists who discovered how drugs work and how to find, extract, or make new ones.

PROJECT:
SMOKING HANDS

Adult
supervision
required

Materials

Protective goggles

A few drops of household ammonia

A few drops of muriatic acid (available at hardware stores and swimming pool supply houses)

Water

Small bowl

2 paper towels or cotton balls

Wastebasket or similar container (optional)

See the video at
http://youtu.be/i21P1XzoLRE

In the photo on the right, I bring my two bare hands together and press so hard that they start to smoke.

Well, at least it looks like that. What is really going on is a chemical reaction between two vapors.

One vapor comes from dampening my left hand with a little bit of household ammonia. The other vapor comes from dampening my right hand with a little diluted hydrochloric acid, known as muriatic acid. To try this yourself, combine a few drops of muriatic acid with twice as much water in a small bowl to further dilute it.
Never use a more concentrated form of hydrochloric acid.
Place a few drops of
ammonia on a paper towel or cotton ball and wipe it onto your left palm. Use another paper towel or cotton ball to wipe the diluted muriatic acid onto your right palm. You should
always wear protective goggles
when handling these chemicalsâ which has the bonus of adding a dramatic sense of danger.

You don't want to do this unless your hands are free of cuts and scratches, as the hydrochloric acid will sting. But it does not attack the layer of dead skin on your palms, so despite the quite reasonable warnings on the bottle, it does no harm. Of course, it's also important to
wash your hands well after the demonstration.
For those who quite sensibly want to avoid putting acid on their hands, the smoke effect can instead be done by placing a few drops of each solution on the paper towels or cotton balls and simply placing them near each otherâsay, in a wastebasket. Whichever technique you use, be careful to
avoid breathing the vapors
that result.

What is going on is a fairly simple chemical reaction. The ammonia solution releases ammonia gas (NH
₃) into the air. The hydrochloric acid releases hydrogen chloride gas (HCl) into the air. The two gases react in the air to produce tiny particles of a white solid called ammonium chloride (NH
₄Cl).

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