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The FDA recently chose not to impose new regulations on bisphenol-A, which has sometimes been used in food packaging. Let’s look at what bisphenol-A is, how it’s used to make materials, and why it can be harmful if people ingest it. Bisphenol-A is shown above. Like many chemicals, its name can tell you how it looks: 

• Bis (two)
• phenol (the red circle on the left: a benzene ring attached to an OH)
• A (acetone, where the 3 carbons in the middle come from)

So bisphenol-A is made by reacting 2 parts phenol with one part acetone. These are all common chemicals that don’t cost a lot, so bisphenol-A isn’t too expensive to make.

What makes it useful is the OH on each side. This makes it like a building block that can attach to something on each side. In other words, it can do something in two places or is bi-functional. 

Building blocks that can attach on both sides can be used to make long chains. And polycarbonate (sometimes called Lexan) is a long molecular chain mostly made of bisphenol-A. Many things, like jet canopies, are made of polycarbonate. Unfortunately it’s also been used in food containers. We’ll talk about that next.

We described how adding salt (or anything) to water increases the boiling temperature. For a similar reason, it also lowers the freezing temperature. By adding salt, the liquid water in equilibrium with ice is not allowed to re-freeze, and eventually all of the ice is melted. The amount of salt used is important, as is the ambient temperature. If it is too cold the salt trick won’t work anymore.

Consider the curve we drew before, focusing on the region near 0 °C. In the zoomed-in version on the right, the vapor pressure of ice is shown along with that of 1) pure water and 2) water with some salt added (a solution). The H2O in question will exist in whichever state has a lower vapor pressure at a given temperature. The point where the curves intersect is the freezing point, and you can see how lowering the liquid curve with salt lowers the freezing point.

We use salt because it’s pretty cheap and safe and for other reasons like that. Other solutes like sugar or alcohol would work, too.

We want to know why throwing salt on an icy sidewalk melts the ice. The first thing to point out is that at any temperature close to the melting/freezing point, there is constantly water freezing and un-freezing at the ice surface. This is called an equilibrium. The trick is to do something that doesn’t allow the water to re-freeze anytime it assumes the liquid state. That’s where the salt comes in.

Anytime you dissolve something in a liquid, you cause two things to happen:

• the freezing point of the liquid decreases
• the boiling point of the liquid increases

Think of all the temperatures where the substance is a liquid as being a range—go below that range and you get a solid, go above and you get a gas. Adding another dissolved substance (i.e. a solute, making a solution) widens this range in both directions.

Let’s consider the boiling point because that might be easier to understand. The vapor pressure over a liquid is exactly what it sounds like: the pressure of the vapor trying to evaporate out of the liquid. It increases with temperature, and when it reaches 1 atmosphere, the liquid evaporates. Adding a solute, like salt or NaCl, lowers the vapor pressure (see the figure). So boiling requires a bit higher temperature.

The reason moles are important can be illustrated this way: what if you had some carbon and some hydrogen? You might want each carbon atom to buddy up with one hydrogen molecule.

How do you make sure each carbon atom and each hydrogen molecule is paired and no one is left out? You can’t just put together equal mass of each one, because they weigh different amounts. What you want to do is add equal moles of each. A mole is 6.022 × 10^23 of the basic chemical entities that make up each. 

Add 12 grams of carbon and 2 grams of hydrogen and you will have equal numbers of each: 1 mole.

A mole is more or less just a number for counting something. The Clear Science staff like to compare it to a dozen. You know that a dozen of something means there are 12 of that thing—for example a dozen doughnuts.

A mole of something is 6.022 × 10^23 of that thing. This is called Avogadro’s number, and if you write it out not in scientific notation, it is:

• 602,214,179,000,000,000,000,000

The standard used to define a mole is the number of carbon atoms in 12 grams of carbon-12. This excellent website has pictures showing moles of various substances, including carbon, which we have borrowed for the graphic above.

You calculate how many moles you have as shown, with the number of grams per mole you read off the periodic table. (Atomic mass, which is the number with decimal points in it.)

We talked about fossil fuels and said that the energy we get from them comes from their chemical bonds. The largest source of energy in the U.S. (and the world) is fossil fuels, a lot of that going toward electricity generation.

We get the energy from fossil fuels through combustion, which is the scientific term for burning. Combustion requires two things: a fuel and an oxidant. In our example the fuel is the fossil fuel octane. The oxidant is oxygen, which comes from the air. Our cars have a fuel tank, but if we were on the moon we would need a fuel tank and an oxidant tank. On Earth we’re spoiled because there’s an oxidant everywhere. (Other substances like chlorine and fluorine are also oxidants.)

Octane and oxygen have more energy in their chemical bonds than the products of combustion, which are carbon dioxide and water. That energy has to go somewhere, so it is released as heat. This is an exothermic reaction. In reality, combustion is rarely perfect, so ash and light and other things are formed, too.

This is why we like fossil fuels: you dig them up out of the ground and they have energy in them ready for the taking. That’s so easy! And easy = inexpensive.

Fossil fuels are a huge fraction of where we get energy. Some of these are used at power plants to make electricity (mainly coal and natural gas) or to power something like a car directly (mainly petroleum). Where does the energy come from in fossil fuels, and why do we use them so much?

Petroleum is a mixture of organic compounds, which are molecules based on carbon. Take octane as an example, shown above. Oct means eight, and octane is a molecule with 8 carbons. (Sometimes people get tired of drawing all the hydrogens in organic molecules, so they draw them as simple stick figures, with corners signifying carbons and the hydrogens implied but not drawn.) Coal (a solid) is mostly longer molecules, and natural gas is shorter molecules.

The energy in fossil fuels is stored in the bonds between the atoms. If you break these bonds, energy comes out. So we break them, and this is how the internal combustion engines in our cars run, as well as the external combustion engines in our power plants.

fyeahchemistry:

Reblogged from goalkeeper007

Happy New Year, Clear Scientists. May all your chemical investigations go swimmingly in 2011.

-The Clear Science staff

The most typical high explosive materials contain nitrogen groups in some form. TNT or tri-nitro-toluene is one most people have heard of. (The benzene ring with a methyl group on top is called “toluene.” It’s “tri-nitro” because it has three NO2 groups on it.) DNT is dinitrotoluene. RDX—a very powerful material—stands for research department explosive, and is actually called cyclotrimethylenetrinitramine.

TATP is showing up in terrorist attacks for two reasons. The first is that it is relatively easy to make using acetone and hydrogen peroxide. Accused terrorist Najibullah Zazi was videotaped shopping at Beauty Supply Warehouse: hydrogen peroxide is used to bleach hair, but it can also make TATP.

The second reason is that many security tests used to detect explosives actually sense the nitro or nitrogen-containing parts of the molecules. TATP, having no nitrogen, can slip through these tests. Scientists are at work developing portable, inexpensive tests to sniff out TATP and explosives like it.  

Triacetone triperoxide or TATP is an explosive material that is recently in the news a lot (even if the name isn’t always mentioned). This material has three peroxide bonds in it. A peroxide bond is an oxygen (O) single-bonded to another oxygen. Peroxides are relatively unstable bonds, and therefore peroxides are prone to detonation. Macroscopically, TATP looks like white crystals.

When a material detonates, a shock wave moving at supersonic speed is created. (This causes the sound of an explosion.) Like many primary explosives, TATP can detonate due to shock, friction, or heat.

TATP was the explosive Richard Reid “the shoe bomber” had in his shoes. It was also the explosive used for the attempted Christmas Day bombing in 2009 on a plane bound for Detroit, and during the 7/7 London Tube bombings in 2005. When we have our shoes x-rayed in the US when we fly, it is TATP they are looking for.