Glossary - Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)

Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)


As Alexa read my answers to her questions, there were occasionally words that were unfamiliar to her. Some of the words I simply define here, but others are best explained by a more detailed examination of the concepts that they describe. So instead of a short a glossary item I will sometimes expand it into a longer explanation.

Albino An animal that lacks pigment (color) in the skin, hair, and eyes, making the skin and eyes pink and the hair white.

Alkali The opposite of an acid. In water, acids donate protons (a hydrogen atom that is missing its electron). Alkalis accept protons. Thus alkalis and acids neutralize one another in water, forming salts.

Bicarbonate The bicarbonate ion is a carbon atom with three oxygen atoms attached and a hydrogen attached to one of the oxygen atoms.


When carbon dioxide reacts with water, it forms carbonic acid.


You can see the carbon dioxide in the molecule (the carbon and the two oxygens) and you can see the water (the two hydrogens and the third oxygen). Acids are things that easily lose a proton (a hydrogen atom without its electron). When carbonic acid loses a proton, it becomes a bicarbonate ion. You can see that the bicarbonate ion is missing the hydrogen nucleus (the proton), but it still has the electron. This gives it a negative charge. An alkali is usually what makes the acid give up the proton. Alkalis are proton-hungry molecules. One strong alkali is called sodium hydroxide.


When sodium hydroxide reacts with carbonic acid, the proton from the carbonic acid swaps places with the sodium atom in the sodium hydroxide. The result is water and sodium bicarbonate, which is the stuff called baking soda. It looks like this:


Bipolar disorder A condition in which a person goes between being in a very good mood and a very bad mood, sometimes very quickly.

Chromatography A way of separating the molecules in a solution according to how well they travel in something like paper.

Capillaries Capillaries are the tiny blood vessels that bring oxygen and food to the cells in your body. Arteries are the larger blood vessels that pump the blood from the heart and lungs to the capillaries. Veins are the large blood vessels that take the blood from the capillaries back to the heart and lungs to get more oxygen.

Corrode To destroy or damage something by chemical reactions. When iron rusts, that is corrosion. When silver tarnishes, that is corrosion. A shiny copper penny becomes dull brown when it corrodes, and sometimes it can turn blue or green, depending on the type of chemical reaction causing the corrosion.

Catalyst A catalyst is something that helps make a chemical reaction go faster, without being used up itself in the reaction.

Delocalized electrons In some molecules, the electrons that form the bonds between the atoms are not stuck to just one atom or one bond but are shared between several atoms. Because they are not “local” to one bond, they are called delocalized.

Diluted Something is diluted (made less concentrated) by adding another substance to it, such as water. If someone’s coffee is too strong, they might dilute it (make it weaker) by adding water.

Detonate To cause something to explode.

Dewar A big Thermos bottle. Long before the Thermos came on the market, James Dewar invented the concept behind it: a bottle inside a bottle, separated by a vacuum, as a way of keeping hot things hot and cold things cold.

Emollient Something that softens or smoothes the skin.

Emulsifier Something that helps oil and water mix into what we call an emulsion. An emulsifier is usually a molecule that has one end that attracts water and another end that does not. The molecules makes a coating around tiny drops of oil or water and keeps them from joining together to make larger drops.

Emulsion A mixture of oil (or fat) and water, in which one of the substances is in the form of tiny droplets inside the other substance. Mayonnaise is an emulsion of oil in water. Butter is an emulsion of water in fat.

Ether There are many kinds of ether, but the most common ones are liquids that are used to dissolve things that don’t dissolve well in water or alcohol.


An example is diethyl ether, which is a liquid similar to alcohol, and it used to dissolve many organic chemicals such as fats and waxes. It is also sometimes used to make people sleep through operations in hospitals.

Equilibrium An equilibrium occurs when opposing forces are balanced (equal). If you are balancing on a tightrope, you want to keep the forces that might tip you over equal on both sides, so you keep your equilibrium and don’t fall off the rope. In chemistry, many reactions can be fairly easily undone. The forces that cause two molecules to join are fighting the forces that would cause them to separate. If some molecules are joining together at the same rate that other molecules are coming apart, the forces are said to be in equilibrium.

Friction Friction is the resistance you feel when you rub two things together. Friction is what helps the brakes in a car slow the car down, and it is what keeps the wheels from sliding on the ground. The friction of a match sliding against the matchbook is what generates the heat needed to light the match.

Gallium An element in the periodic table of elements. It is a metal that melts in your hand.

Gradient A gradual change—for instance, a gradual change in voltage—that causes the things that are affected by it slide down it. A playground slide is a gravity gradient that causes you to slide down it, since you are affected by gravity.

Gypsum Gypsum is calcium sulfate.


It is the white rock inside sheetrock, the wallboard that many houses use to make their walls. It is similar in many ways to chalk.

Hemoglobin Hemoglobin is the oxygen-carrying protein found in red blood cells. It is what makes blood with lots of oxygen look red and blood with little oxygen (such as that in the veins in your wrist) look blue.

Henna Henna is a plant that contains a molecule in its leaves called lawsone.

Lawsone is a reddish brown dye that binds strongly to proteins in skin, hair, and fingernails. It is used for temporary tattoos and skin decorations, as a hair dye, and as a fingernail colorant. It is also used to dye leather. In the plant, it absorbs ultraviolet light strongly and protects the plant from sun damage.


Infrared There is more to light than the rainbow of colors we can see. There is light that is beyond the red end of the spectrum, called infrared light, and there is light beyond the violet end, called ultraviolet light. Humans can’t see either of these kinds of light. But we feel infrared light as heat, and ultraviolet light is what causes sunburns. There are other types of light beyond infrared, such as microwaves and radio waves. There are also other types of light beyond ultraviolet, such as X-rays and gamma rays.

Ionic A substance (like table salt) that breaks up in water to form ions. Detergents are categorized as ionic surfactants (such as sodium lauryl sulfate) or nonionic surfactants (such as cetyl alcohol or polysorbates). Ionic surfactants work best in warm or hot water, while nonionic surfactants can work in cold water.

Linear In a line. Molecules can be a linear string of atoms, or they can be a branching structure like a tree, or they can even have rings of atoms or complicated webs. But linear molecules are among the simplest types.

Lipase An enzyme (a type of protein) that breaks down fat. It is used in digesting food. Fats and oils are called lipids, which is where lipase gets its name. Several other words that begin with lip also refer to fats. For example, a cosmetic surgeon might use a type of vacuum to suck fat out of a movie star, in a process called liposuction.

Lubricant A substance, such as oil or grease, that is used to reduce friction. Cars use oils and grease to lubricate their parts, but people also use lubricants on their skin to reduce irritation caused by rubbing. Lubricants make things slippery.

Lubrication Using or applying a lubricant to make something slippery.

Lye Lye is the common name for sodium hydroxide, a powerful alkali used in many things, such as making soap out of fats. It is used in the home as a drain cleaner.

Microorganisms Tiny (microscopic) little living things. Bacteria, algae, mildew, yeast, and tiny animals called protozoa, as well as tiny insects and similar animals that are too small to see are all organisms in the micro world, so we call them microorganisms.

Melanin The main pigment in the skin and hair. It is what makes you tan, and it is what is missing in the gray hair of older people.

Mica Mica is a type of rock that forms very thin crystal sheets that look and feel like plastic. The flat sheets reflect light and are what makes the sand at the beach sparkle.

Monomer A molecule that links up with other monomers to form polymers, long chains of molecules. Mono means one, and poly means many.

Mucus Slime. Snails make it to walk on, and people make it in their noses to collect dust before it can get in the lungs. When you have a cold, it is what you sneeze into the tissue.

Olfactory cells The cells in your nose that detect odors and perfumes.

Opaque An opaque object or substance is something that completely blocks light. If you can see through something, it is transparent. If you can’t see through it but light still comes through (like a thin piece of paper), we say it is translucent. But something like wood or metal that completely blocks the light is opaque.

Opium Opium is a drug made from a species of poppy flowers. Drugs made from opium are used to numb pain and to induce sleep.

Polymer See monomer.

Pores Small holes. We have pores in our skin so we can sweat and release oils to lubricate skin. Insects have pores in their skin so they can breathe. Plants have pores in their leaves so they can breathe. Something like a sponge, which has many pores and lets water through it, is called porous.

Rancid When foods containing fats or oils spoil, the oils combine with oxygen in the air to form bad-smelling and badtasting molecules. We say the food has gone rancid, which is just a way of saying that a fatty food has spoiled.

Reagent Something added in order to cause a chemical reaction or to see if a reaction happens.

Solvent A liquid that can dissolve something, Examples are water, alcohol, paint thinner, acetone, turpentine, and gasoline.

Soot Soot is the black stuff in smoke. It is made of tiny particles of carbon, the black element that gives charcoal its color. Almost any fuel that contains carbon can produce soot if there is not enough oxygen for it to burn completely.

Statins Statins are a type of drug used for reducing cholesterol in the blood of people, in the hope of reducing the risk of a heart attack.

Subtle Difficult to detect or describe, such as a subtle odor. So delicate or precise that it can be difficult to describe, such as a subtle difference between a California accent and a Colorado accent.

Surfactant A molecule such as soap, with one end that attracts water and one end that does not. A surfactant is active at the surface between oil and water and keeps droplets from coming together.

Thiol An organic (carbon-containing) molecule that contains a sulfur atom bound to a hydrogen atom. Thiols often have strong odors. The odor of garlic is due to thiols. Thiols are added to the gas used for cooking so that humans can detect the odor if there is a gas leak.

Voltage The pressure on electrons that make them flow. A 9 volt battery pushes electrons harder than a 1.5 volt battery.