Tag Archives: Molecules

The Coolest Molecules

CAUTION: This experiment uses dry ice (-109˚F) and liquid nitrogen (-321˚F). Proper safety equipment should always be used when handling these substances.

Physics tells us that pressure, volume and temperature are all linked when talking about gases. So what does this have to do with solid carbon dioxide (dry ice) and liquid nitrogen? When dry ice is placed into a balloon at room temperature, which is then tied off, it will start to warm up.

molecules

Since the ambient air temperature is roughly 65˚F, the air that surrounds the balloon is more than 150 degrees warmer than the dry ice! This hug difference adds energy to the dry ice turning it into gaseous carbon dioxide through the process of sublimation. Sublimation is the phase transition of a substance directly from the solid to the gas phase without passing through the intermediate liquid phase.

molecules cool

Now that there is a balloon full of carbon dioxide gas we can cool it down with something colder than dry ice. This is where liquid nitrogen comes in. The balloon gets dunked into a bowl full of the -321˚F liquid! Cooling the gas in the balloon down means that it loses energy making the molecules start to clump, making the balloon lose volume. It will turn the carbon dioxide gas back into a solid through the process of deposition. Deposition is basically the opposite of sublimation, turning the gas directly into a solid.

molecules done

This process of cooling and warming to change the balloon’s volume can be repeated over and over again. Or, with the inflated balloon, dunk it in the bowl of liquid nitrogen, take it out, and before it can expand again, rip it open to see the solid carbon dioxide for yourself!

Written By: Mimi Garai

 

Is it a Microwave or a Shrink Ray?

I’ll be honest: This one blew me away the first time I saw it! What is going on here? It all has to do with polymers, which are basically long chains of repeated molecules, which you can learn more about here.

Just to re-iterate: This is not dangerous to you, but it is dangerous to the microwave!

Microwave Magic

These polymers have some interesting properties that we need to understand, and then this will become much simpler. As we have seen before, temperature can be an important part of chemistry. That is also important here! Let’s start by talking about something a more familiar polymer: protein!

We all have lots of protein in our bodies which perform many different functions. These functions are determined by their shapes, which are in turn determined by the specific molecules that make them up. However, if proteins are exposed to high temperatures or acidic conditions, they lose their shape and just uncoil into a big mess. This is called denaturation, is actually a good thing for us. Human stomachs are highly acidic, and when you eat food with protein in it, this allows the protein to be broken down so that it can be used.

image002

A similar thing happens with the polymers in the bag*. When these huge chains are hot, they become very flexible. Left to their own devices, they will tangle up and clump into a polymer mess. Alternatively, in this flexible state they can be easily manipulated a different shape. When they are cooled down, they maintain this shape.

This gives us all the tools we need to understand the behavior of these bags in the microwave. These bags contain a polymer skeleton surrounded with foil and paint. When the bags are manufactured, they are heated up and stretched out before being cooled off. The result is that the long polymers in the bag are locked into long straight lines forming the structure of the bag.

In the microwave, they get HOT. Without anything to hold them in position, they collapse into their natural shape: a big clump. As the bag’s polymer skeleton collapses, the bag itself shrinks dramatically. The results are astounding!

Written By: Scott Alton

Microwave Magic Display

*Note: If you are reading carefully, it may seem like this is the exact opposite of the protein. This is because proteins are heated up to the point where they collapse to the appropriate shape at body temperature, whereas for these polymers that temperature is much higher. If these polymers were to get even hotter, they would exhibit similar denaturation behavior. Similarly, cooling the protein well below body temperature would lock them into their current shape. The same thing is happening, it is just on different temperature scales.

10 Things You Didn’t Know About Nylon

Nylon was patented on February 16, 1937 by Wallace Carothers. Almost exactly one year later, it hit the shelves in the form of toothbrush bristles. In the intervening years, it has been used for packaging food, building car engines, clothing, fishing line, 3D printing… it even went to the moon! But just what is this multipurpose material?

moonflag

Buzz Aldrin and the Nylon flag that they brought to the moon on Apollo 11. Note the rigid support rod at the top to support the flag in the near vacuum conditions. Credit NASA.

This is a model of Nylon 6,6; the most common industrial form. Each molecule is relatively small and simple, but they bind together into long chains when the negative nitrogen bonds to the positively charged carbon at the base of another chain, similar to metallic links in a traditional chain. These long chains in chemistry are called polymers, and nylon is the name used for a large family of slight variations on this idea.

Polymerization

Caption: Models of Nylon 6,6 chaining together. Red is oxygen, blue is nitrogen, black is hydrogen, and the carbon chain backbone is white. This process happens through a chemical reaction called condensation polymerization, because a molecule of water is produced when the two connect.

One reason that nylon is so useful is that it is a thermoplastic. Around 500oF it begins to liquify. This allows it to be drawn out into long very thin strings. Nylon fabric is just like normal fabric, except that it is made of these tiny thermoplastic fibers. As a synthetic material, it doesn’t mold. It is also waterproof and quick drying, making it ideal for a lot of lightweight outdoor clothing. With all of the rain we are supposed to get this year, this is a good time for appreciating nylon!

Nylon Print

This nylon molecule model is made out of…Nylon!

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