Breaking Down MCAT Chemistry Discrete Questions

Session 36

My name is Dr. Ryan Gray and I am joined again by Blueprint MCAT (formerly Next Step Test Prep)‘s MCAT guru, Bryan, as we look at a few general chemistry discrete questions and break them down to help you on your MCAT journey.

[01:46] General Chemistry MCATQuestion #15:

Which of the following particles is expected to have the least mass:

(A) Alpha particle

(B) Beta particle

(D) Gamma particle

Bryan’s Insights:

A gamma particle is such a high energy photon, it has no mass. The physicists would insist that it has no rest mass. But the MCAT is not that picky. Hence, the right answer is (D) Gamma particle since it has no mass at all.

An alpha particle is two protons and two neutrons. Sometimes called the helium nucleus, the alpha particle is the heaviest. Beta particles and positrons have just a little bit of mass because their electrons are antielectrons.

An alpha particle is two protons and two neutrons.Click To Tweet

Pilots up in the air have got less atmosphere protecting them, so they’re exposed to more radiation. It’s funny how the general population doesn’t know much about radiation so they freak out whenever they hear the word because radiation is always out there and we’re dealing with it.

[03:44] General Chemistry MCAT Question #31:

Which of the following is a weak acid in aqueous solution?

(A) HF

(B) HCl

(D) HI

Bryan’s Insights:

This is one where the MCAT is going to expect you to know your classic strong acids. Hydrochloric acid, hydrobromic acid, and hydroiodic acid are all strong acids. Some other strong acids the MCAT is also going to expect you to know are sulfuric acid, nitric acid, and perchloric acid, the classic oxygen-containing acids.

The MCAT expects you to know your strong acids.Click To Tweet

But remember that among the halogens, HF is weird because it’s actually a weak acid. In this case, the fluorine is so strongly electronegative that it’s not willing to give up its proton so it doesn’t act as an acid in water.

[04:47] General Chemistry MCAT Question #45:

Which of the following electronic transitions for hydrogen would result in the emission of a quantized amount of energy?

(A) n=1 – n=2

(B) n=2 – n=3

(D) n=4 – n=6

Bryan’s Insights:

The way to answer this question is by playing the classic MCAT game of which of these is not like other or which one of these does not belong. Forget any of your science because you just have to look structurally which answer choice is different.

In this case, the answer choice that stands out is (C) because all the rest have numbers going up. Hence, C is the right answer.

If the electron is in a high energy state 5 drops down to a principal quantum number 4, it releases energy. That energy has got to go somewhere as per the law of conservation of energy, and it gets released as a photon.

[06:00] General Chemistry MCAT Question #47:

Phosphorous acid, a common ingredient used for potable water treatment has a molecular formula of:

(A) H3PO5

(B) H3PO4

(D) H3PO2

Bryan’s Insights:

The MCAT is going to expect you to know your general chemistry nomenclature. Just to give you a review of this topic, which we’ve previously talked about, phosphorous acid would be H3PO3.

Know your general chemistry nomenclature for the MCAT.Click To Tweet

The molecule that you absolutely have to know as you walk into the MCAT is H3PO4 which is phosphoric acid. So phosphorous acid has one less oxygen. H3PO2 is hypophosphorous acid, with one less oxygen again, its hypo-. H3PO5 is perphosphoric acid. So the one with most oxygens has the prefix “per-” and the suffix “-ic.”

The nomenclature doesn’t specifically relate to the number each time because it can change depending on the number of the molecule. For instance, perchloric acid is HClO4, chloric acid is HClO3, chlorous acid is HClO2, and hypochlorous acid is HClO. It’s about the relationships between them rather than the total number of oxygens.

[08:47] Blueprint MCAT (formerly Next Step Test Prep)

Practice tests are a huge part of preparing for the MCAT. Blueprint MCAT (formerly Next Step Test Prep) has ten full-length practice tests that you can take and learn from. Next Step simulates the real AAMC MCAT test and that is critical to practicing for the MCAT.