Kaplan MCAT General Chemistry Review

“Salting the water makes the pasta cook faster because the salt raises the boiling point. It’s chemistry—it’s a colligative property.” My colleague stared me down, as if the intensity of his gaze gave further credence to his pronouncement. It was late on a Friday afternoon, about 5:00 P.M., and the science of cooking had become the topic of discussion that would carry us through the final hour of the workweek. However, here we were, arguing over the relative merits of culinary and scientific justifications for adding salt to pasta water. We were two opposing camps: one side arguing that adding salt to the water served no real purpose other than to flavor the pasta as it absorbed the water; the other side—the one of my colleague and his compatriots—fighting in the name of science. Finally, we agreed on a plan toward resolution and a lasting peace. We would calculate the actual chemical impact of the salt in the water and answer the question Why add salt to pasta water? once and for all.

Well, you can figure out the details of the calculation if you are so inclined, but suffice it to say that I wouldn’t be telling you this story if I hadn’t been proven correct. Our calculation showed that the amount of salt that most of us would probably consider a reasonably sufficient quantity for a large pot of boiling water had minimal impact on the boiling point temperature of the resulting solution. To be clear, the addition of the salt did raise the boiling point temperature—and even those of us arguing against the “scientific justification” never denied that it would. Nevertheless, the calculated rise in boiling point was exceedingly small, because the solution we imagined had such a low molality. The truth of the matter is this: Adding salt to cooking water in reasonable amounts does not measurably increase the boiling point temperature or decrease the cooking time. The salt merely flavors the food as it cooks in the dilute solution.

Why introduce a book of general chemistry for the MCAT review by telling you a story about food preparation? Am I telling you this simply to showcase an instance in which I won an argument? No, it’s because chemistry is the study of the stuff of life or, to put it more properly, the nature and behavior of matter. Chemistry is the investigation of the atoms and molecules that make up our bodies, our possessions, the world around us, and of course, the food that we eat. There are different branches of chemistry, two of which are tested directly on the MCAT—general inorganic chemistry and organic chemistry—but ultimately all investigations in the realm of chemistry are seeking to answer the questions that confront us in the form (literally, “form”: the shape, structure, mode, and essence) of the physical world that surrounds us.

At this point, you’re probably saying the same thing you say when talking about physics: But I’m premed. Why do I need to know any of this? What good will this do me as a doctor? Do I only need to know this for the MCAT? Let me make it clearer for you: How can you expect to be an effective doctor for your patients—who are made of the organic and inorganic stuff—unless you understand how this stuff makes up and affects the human body?

So, let’s get down to the business of learning and remembering the principles of the physical world that help us understand what all this stuff is, and how it works, and why it behaves the way it does, at both the molecular and macroscopic levels. In the process of reading through these chapters and applying your knowledge to practice questions, you’ll prepare yourself for success not only on the Physical Science section of the MCAT but also in the medical care of your patients and the larger communities you will serve as a trained physician.

MCAT Expertise

The building blocks of the atom are also the building blocks of knowledge for the General Chemistry concepts tested on the MCAT. By understanding these interactions, we will be able to use that knowledge as the “nucleus” of understanding to all of General Chemistry.

This first chapter starts our review of general chemistry with a consideration of the fundamental unit of matter, the atom, and the even smaller particles that constitute the atom: protons, neutrons, and electrons. We will also review the two models of the atom with a particular focus on how the two models are similar and different.

Subatomic Particles