Bacon and eggs. A bacon, lettuce, and tomato sandwich. Bacon crumbles sprinkled over roasted Brussels sprouts. Even a doughnut topped with maple icing and, you may have guessed, bacon. Hungry yet? These are all food items that have one time or another been on my menu. The common thread, of course, is the crispy, tasty addition of bacon. How does bacon go from its initial properties and appearance to the flavorful, delicious cooked product that many of us love to eat? Continue reading “ChemMatters Infographic: Why Bacon Smells So Good”
To make sense of the endless variety of chemical reactions that can occur, chemists have devised many ways to categorize reactions that seemed similar. One early attempt to explain reactions related to combustion or the burning of various substances involved speculation that a fire-like substance called phlogiston was released. One big problem was the phlogiston could not be detected, and an even bigger problem was that substances that underwent combustion actually gained weight! Continue reading “ChemMatters Infographic: A Quick Guide to Organic Reactions”
The Art of Estimation
When I was in high school, in the days before electronic calculators were available, we learned how to use mechanical slide rules (see ChemMatters, April 2004, p.4) for our calculations. While they were great for getting a good answer to math problems, they didn’t keep track of the decimal place. That had to be done by keeping track of an order of magnitude estimate of the answer. Continue reading “Fermi Questions: Back of the Envelope Calculations”
After a long, dry summer, a rainstorm is often welcomed. The first rain of the season always seems special, and a bit different, especially because they are often accompanied by a unique smell. You’ve probably smelled this type of rain before. It has an earthy and sharp, sweet smell that is unlike any other. And it doesn’t happen with the rainy days that follow. The smell is distinctive enough to have its own name, petrichor, pronounced, peˌtrīkr. The February issue of ChemMatters magazine has a wonderful infographic about petrichor that was developed by an ACS ChemClub member.
This term was coined bin 1964 by two Australian researchers, Isabel Joy Bear and Richard G. Thomas, for an article in the journal Nature. The term comes from the Greek word petra meaning stone, and ichor from Greek mythology, meaning the fluid that flows in the veins of the gods.
It may seem odd that rain would have a smell at all, because rain starts out as pure water, which has no smell. Bear and Thomas reasoned the smell must have something to do with what happens as the raindrops hit the ground. They duplicated this process in their lab by drying samples of clay earth and then subjecting it to varying amounts of moisture. By analyzing the compounds that cause the odor, researchers have identified the source of petrichor.
It turns out that during dry weather, soils collect volatile plant oils (such as terpenes and fatty acids) that are released into the air when the rain lands on them.
Another contributor is the compound named geosmin, which is formed by bacteria in the soil. The human nose is very sensitive to geosmin and can detect it in as little as five parts per million (ppm).
And finally, ozone (O3) and nitric oxide (NO) that occur naturally in the air contribute to the smell of rain, as they are absorbed by the rain as it falls.
It is interesting that in India the perfume industry in the region of Kannauj hasbeen making a perfume by distilling these same elements from the clay soils in the area. it is known asmitti attar orEarths perfume. It has the same smell as petrichor.
While the chemical nature of petrichor has been well understood for several decades, it wasn’t until 2015 that scientists understood the mechanism of how the odor was released into the air. Researchers from the Massachusetts Institute of Technology (MIT) used high speed cameras to film raindrops hitting the ground. They found that when the raindrops hit the ground they form create aerosols in air bubbles inside the drop, like gases in a glass of soda pop. These bubbles burst and escape into the air, making Earth’s own perfume.
This graphic is a winning entry in the inaugural ChemClubInfographic Contest. ACS ChemClubs were challenged to take a chemistry topic and turn it into an original informational graphic. Entries were judged on originality, and the ability to convey accurate science details clearly and creatively. This infographic was conceived by Michelle Prunier from Guilderland High School in Guilderland Center, NY. It appears in the February 2017 issue of ChemMatters.
All of us realize we are surrounded by “stuff” or more precisely, matter. But getting a handle on the various types of matter around us is a different story. It is a little like walking down a shopping mall with stores that have no store signs labeling what kind of goods they sell. All you can do is look through the windows to get an idea of what they offer for sale.
To sort out the kinds of stuff that surround us, chemists look at the physical and chemical properties of matter and classify it in to various groups.
One of the largest distinctions is between pure substances and mixtures. Pure substances (or just substances) are homogeneous (that is, the same throughout) and have a definite composition, which means they have simple whole number ratios (by mass) between elements that make them up. These are the elements (like gold or carbon) and compounds,(like salt or calcium carbonate) that we tend to spend a lot of time studying in chemistry, because they are the building blocks for all the other types of matter we encounter.
Mixtures on the other hand are a bit messier. They are combinations of two or more materials. This means mixtures can usually be separated back into their original materials by physical processes. A good non-chemical example of a mixture is a jar of mixed nuts, or a drawer with miscellaneous kinds of screws, bolts and washers.
Solutions, suspensions and colloids are similar in that they are combinations of smaller amounts of solute in larger amounts of solvent. The main reason for the varying characteristics among them is the particle size of the solutes.
Emulsions are a special case. An emulsion can be made with two liquids that would normally not mix, such as oil and water. In the case of mayonnaise an egg yolk, which contains the emulsifier lecithin, is used to suspend the oil in tiny droplets. The lecithin coats the oil droplets so its “fat loving” side is on the inside with the fat, while the “water loving” side faces the aqueous solvent side.
Although solutions are often introduced with examples such as sugar dissolving in a pitcher of water for Kool-Aid, solute-solvent relationships can involve various phases beyond solids in liquids.
Air is a common example of a gas-gas solution and soda is carbon dioxide gas dissolved in liquid water. Hydrogen gas can dissolve in palladium metal as an example of gas-solid solutions. You might be wearing a solid-solid solution right now in the form of alloy metals used in jewelry. Similar phase combinations occur in suspensions and colloids. A nice challenge would be to come up with other everyday examples of various phases in solutions, suspensions, colloids or other mixtures.
Finding other examples could help sort out the messy mix of mixtures that surround us!
This graphic is a winning entry in the 2015-2016 ACS ChemClubs/ChemMatters Infographic Contest. Students, teachers, and other chem enthusiasts were challenged to take a chemistry topic and turn it into an original informational graphic. Entries were judged on originality, and the ability to convey accurate science details clearly and creatively. This infographic was conceived by Aaron Herrera and Emerald Rawls from Mapleton Expeditionary School of the Arts in Thornton, CO.