Kaplan MCAT General Chemistry Review

4) Plug the concentrations into the K_spexpression and solve.

K_sp = [Ca²⁺][F^-]²

K_sp = (10^-8)(10^-2)² = 10^-12

The “actual” value for the K_sp is 3.9 × 10^-11, so we are quite close.

Art Credits for General Chemistry

Figure 1.1—Image credited to Slim Films. From The Coming Revolutions in Particle Physics by Chris Quigg. Copyright © 2008 by Scientific American, Inc. All rights reserved.

Figure 1.2—Image credited to Jared Schneidman Designs. From The Earth’s Elements by Robert P. Kirshner. Copyright © 1994 by Scientific American, Inc. All rights reserved.

Figure 6.1 (Intact egg)—Image credited to Richard Drury/Getty Images. From The Cosmic Origins of Time’s Arrow by Sean M. Carroll. Copyright © 2008 by Scientific American, Inc. All rights reserved.

Figure 6.1 (Slightly cracked egg)—Image credited to Graeme Montgomery/Getty Images. From The Cosmic Origins of Time’s Arrow by Sean M. Carroll. Copyright © 2008 by Scientific American, Inc. All rights reserved.

Figure 6.1 (Egg cracked in half)—Image credited to Jan Stromme/Getty Images. From The Cosmic Origins of Time’s Arrow by Sean M. Carroll. Copyright © 2008 by Scientific American, Inc. All rights reserved.

Figure 6.1 (Egg half with yolk)—Image credited to Michael Rosenfeld/Getty Images. From The Cosmic Origins of Time’s Arrow by Sean M. Carroll. Copyright © 2008 by Scientific American, Inc. All rights reserved.

Figure 6.1 (Smashed egg with seeping yolk)—Image credited to Jonathan Kantor/Getty Images. From The Cosmic Origins of Time’s Arrow by Sean M. Carroll. Copyright © 2008 by Scientific American, Inc. All rights reserved.

Figure 6.1 (Over easy egg)—Image credited to Diamond Sky Images/Getty Images. From The Cosmic Origins of Time’s Arrow by Sean M. Carroll. Copyright © 2008 by Scientific American, Inc. All rights reserved.

Figure 8.1—Image credited to Don Foley. From The Ice of Life by David F. Blake and Peter Jenniskens. Copyright © 2001 by Scientific American, Inc. All rights reserved.

Figure 8.6—Image credited to Daniels and Daniels. From The Amateur Scientist: Tackling the Triple Point by Shawn Carlson. Copyright © 1999 by Scientific American, Inc. All rights reserved.

Part II

Practice Sections

INSTRUCTIONS FOR TAKING THE PRACTICE SECTIONS

Before taking each Practice Section, find a quiet place where you can work uninterrupted. Take a maximum of 70 minutes per section (52 questions) to get accustomed to the length and scope.

Keep in mind that the actual MCAT will not feature a section made up of General Chemistry questions alone, but rather a Physical Sciences section made up of both General Chemistry and Physics questions. Use the following three sections to hone your General Chemistry skills.

Good luck!

Practice Section 1

Time—70 minutes

QUESTIONS 1–52

Directions: Most of the questions in the following General Chemistry Practice Section are organized into groups, with a descriptive passage preceding each group of questions. Study the passage, then select the single best answer to the question in each group. Some of the questions are not based on a descriptive passage; you must also select the best answer to these questions. If you are unsure of the best answer, eliminate the choices that you know are incorrect, then select an answer from the choices that remain.

PASSAGE I (QUESTIONS 1–9)

Acid rain is a meteorological phenomenon that is defined as any type of precipitation that is unusually acidic. Rain is naturally slightly acidic (pH = 5.2) due to the reaction of water with environmental CO₂ gas to produce carbonic acid. Experts agree that it is mainly a result of pollution, particularly sulfur and nitrogen compounds that react in the atmosphere to produce acids. These reactions are shown below:

SO₂ + OH· HOSO₂·

HOSO₂· + O₂ HO₂· + SO₃

SO₃ + H₂O H₂SO₄

NO₂ + OH· HNO₃

A college chemistry student was studying outside one day, sipping on a glass of purified water with a pH of 7, when a sudden rainstorm occurred. Wanting to protect his books, he ran inside with them, leaving the glass out on the ledge of his deck. While studying inside, he reviewed the section on acids and bases and decided to run some tests on the glass of water outside, which had collected approximately 100 mL of rainwater mixed with 300 mL of purified water.

1. The acidity of rain is based on the acidity of the contaminating pollutants. Would H₂SO₄ or HNO₃ produce a more acidic rain?

A. H₂SO₄, because it has a lower pK_a.

B. HNO₃, because it has a lower pK_a.

C. H₂SO₄, because it has a greater pK_a.

D. HNO₃, because it has a greater pK_a.

2. What is the approximate concentration of H⁺ in normal rain due to the reaction between CO_2(g) and H₂O_(l)?

A. 8 × 10^-3 M

B. 6 × 10^-5 M

C. 7 × 10^-6 M

D. 2 × 10^-7 M