MCAT General Chemistry Review
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.
Practice Section 1
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 pKa.
B. HNO3, because it has a lower pKa.
C. H2SO4, because it has a greater pKa.
D. HNO3, because it has a greater pKa.
2. What is the approximate concentration of H+ in normal rain due to the reaction between CO2(g) and H2O(l)?
A. 8 × 10-3 M
B. 6 × 10-5 M
C. 7 × 10-6 M
D. 2 × 10-7 M
3. Under which of the following classifications of “acid” does H2SO4 fall?
A. I only
B. II only
C. II and III only
D. I, II, and III
4. Suppose a few drops of acid rain fell on an open cut in the student’s hand. Would the bicarbonate (HCO3-) that exists in blood have any effect?
A. Yes, bicarbonate will buffer by accepting a H+ ion.
B. Yes, bicarbonate will buffer by donating a H+ ion.
C. No, bicarbonate does not act as a buffer.
D. There is not enough information in the passage to determine the correct answer.
5. If the rainwater that mixed with the pure water had original concentrations of [H2SO4] = 2 × 10-3 M, [HNO3] = 3.2 × 10-3 M, what is the approximate final pH of the glass of water?
6. Which of the following is an INCORRECT pair of an acid and its conjugate base?
A. H2SO4 : HSO4-
B. CH3COOH : CH3COO-
C. H3O+ : H2O
D. H2CO3 : CO2
7. With which of the following statements would the student most likely NOT agree?
A. Acid rain has increased in frequency and intensity over the past 150 years.
B. Radicals play an integral role in the development of acid rain.
C. Acid rain lessens the conductive capabilities of water.
D. Acid rain is dangerous to the environment even though rain is naturally acidic.
QUESTIONS 8–9 ARE BASED ON THE FOLLOWING TITRATION CURVE:
8. What is the approximate ratio of pKa1:pKa2 for H2CO3?
9. What is the approximate ratio of equivalence points for H2CO3?
PASSAGE II (QUESTIONS 10–17)
The specific heat of a substance, c, measures the amount of heat required to raise the temperature of the mass of substance by a specific number of degrees. In certain cases, the chemical literature reports specific heat in terms of moles. Specific heat differs from heat capacity, a measurement of the amount of heat required to change the temperature of an object by a specific number of degrees.
In SI units, specific heat indicates the number of joules of heat needed to raise the temperature of 1 gram of the substance by 1 Kelvin. The specific heat of water reported in the chemical literature is 4.184 Jg-1K-1. Specific heat can be measured by a calorimeter, a device that insulates a sample from atmospheric conditions in order to measure the change in the sample material’s temperature over a set interval.
A student used a coffee cup calorimeter to compare the specific heat of water to the specific heat of a commercial fruit punch. The punch is made from a mixture of sugar water and powder flavoring. The student’s coffee cup calorimeter used a stack of two foam coffee cups and a thermometer, which the student stuck through a hole in a plastic lid covering the top cup in the stack. Such calorimeters are inexpensive and accurate experimental substitutes for industrial bomb calorimeters, which hold samples at constant volume to measure water temperature changes under high-pressure conditions.
To calibrate the calorimeter, the student combined known quantities of hot and cold water in the coffee cup until the thermometer read a steady temperature, as described in Table 1.
Table 2 summarizes the specific heat data the student collected for the water and the fruit punch using the calibrated coffee cup setup.
10. Which of the following values reports the molar specific heat of water from the chemical literature?
A. 4.184 Jmol-1K-1
B. 75.31 Jmol-1K-1
C. 4184 Jmol-1K-1
D. 75310 Jmol-1K-1
11. What measurement is also an intrinsic property of fruit punch?
12. What is the heat capacity of the student’s coffee cup calorimeter?
A. 4.184 J/°C
B. 24.6 J/°C
C. 861 J/°C
D. 0.0246 J/°C
13. Suppose the student breaks his glass alcohol thermometer in the lab. The lab instructor’s only available replacement is a mercury thermometer. How would this change to the experimental setup affect the student’s measurements?
A. The calorimeter would measure a higher specific heat.
B. The calorimeter would measure a lower specific heat.
C. The thermometer would give a less precise specific heat measurement.
D. There would be no change to the specific heat measurement.
14. Which of the following rationales BEST explains why the student calibrated the coffee cup calorimeter before the experiment?
A. The coffee cup calorimeter can absorb heat.
B. The coffee cup calorimeter does not dry between uses.
C. The coffee cup calorimeter’s thermometer does not produce precise values.
D. The coffee cup calorimeter contents do not always reach equilibrium.
15. Suppose the student decided to compare his sugar water measurements to those from a salt water sample, in which 16 g NaCl replace the 16 g table sugar in Trial 2. How would the specific heat of this salt water differ from that of sugar water?
A. The calorimeter would measure a lower specific heat.
B. The calorimeter would measure a higher specific heat.
C. The calorimeter would measure the same specific heat.
D. The calorimeter would decompose.
16. Which of the following experimental quantities MUST remain constant in Trial 1 in order for the student to obtain a specific heat for water close to the literature value?
A. I only
B. I and III only
C. II and III only
D. I, II, and III
17. For which of the following laboratory measurements would a bomb calorimeter be more useful than a coffee cup calorimeter?
A. To measure the specific heat of salt water
B. To measure the specific heat of ethanol
C. To measure the specific heat of water vapor
D. To measure the specific heat of copper
QUESTIONS 18–21 ARE NOT BASED ON A DESCRIPTIVE PASSAGE.
18. Given the balanced equation, Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g), how many liters of hydrogen gas are produced at STP if 3 moles HCl are reacted with excess magnesium?
A. 1.2 L
B. 33.6 L
C. 2.4 L
D. 44.8 L
19. Increasing the temperature of a system at equilibrium favors the
A. exothermic reaction, decreasing its rate.
B. exothermic reaction, increasing its rate.
C. endothermic reaction, increasing its rate.
D. endothermic reaction, decreasing its rate.
20. Which type of radiation has neither mass nor charge?
21. Iron rusts more easily than aluminum or zinc because the latter two
A. form self-protective oxides.
B. form extremely reactive oxides.
C. are better reducing agents.
D. are good oxidizing agents.
PASSAGE III (QUESTIONS 22–29)
Product BD can be prepared by the following reaction mechanism, which is known to exhibit first-order kinetics with respect to each of the reactants:
1. AB(g) + C(g) A(g) + BC(aq) (fast)
2. BC(aq) + D(aq) + heat BCD(aq) (slow)
3. BCD(aq) + heat C(aq) + BD(aq) + heat (fast)
To determine the effect of heat on the overall reaction, a scientist mixed one equivalent each of compounds AB, C, and D with excess water in identical reaction flasks at five different temperatures. The scientist then recorded the rate of formation of the product at each temperature, as well as the final concentration of that product when the reaction reached equilibrium, shown in Table 1:
Rate of Formation of BD
[BD] at Equilibrium
The scientist ran a second experiment in which she omitted the equivalent of compound C from the reaction mixture. The results of this second experiment are shown in Table 2:
Rate of Formation of BD
[BD] at Equilibrium
22. Compound C’s most likely role in this reaction is to
A. donate an electron to compound B.
B. accept an electron from compound B.
C. decrease the amount of energy required for compound D to bind with compound B.
D. decrease the amount of energy required for compound A to dissociate from compound B.
23. Which of the following compounds could the scientist add to the initial reaction mixture to increase the yield of product BD?
A. Compound A
B. Compound B
C. Compound C
D. Compound D
24. Which of the following graphs best demonstrates the effect of temperature on the equilibrium constant of the reaction in the passage?
25. The scientist runs a third experiment in which she adds two equivalents of compound AB to one equivalent each of compound C and compound D at 80 °C. What is the expected rate of formation of product BD under these conditions?
A. 9.1 mmol/hr
B. 18.1 mmol/hr
C. 36.2 mmol/hr
D. 54.3 mmol/hr
26. If no catalyst is present, what is the approximate minimum temperature range in which the reaction in the passage would immediately reach its activation energy?
27. What reaction type best describes step 1 of the reaction mechanism in the passage?
A. Double replacement
B. Single replacement
28. What step of the reaction mechanism from the passage would be affected most by a change in pressure?
A. Step 1
B. Step 2
C. Step 3
D. All steps to a roughly equal extent
29. Which of the following statements must be TRUE for the overall reaction in the passage?
I. H > 0
II. G > 0
III. S < 0
A. I only
B. III only
C. I and II only
D. I, II, and III
PASSAGE IV (QUESTIONS 30–36)
A few years before Dmitri Mendeleev published the first rendition of the modern periodic table, the English chemist John Newlands suggested the concept of periodicity when he arranged all of the then-known elements by increasing atomic weights and found that every eighth element exhibited similar properties. He dubbed his principle the “Law of Octaves” and created a chart in which the elements would be organized into groups of seven. In this chart (below), the eighth element would appear immediately to the right of the previous element that shares its properties:
Newlands’ discovery was initially dismissed as a coincidence. Soon afterward, Mendeleev created a more elaborate table that was eventually refined into the version that is common today. This table also arranged the elements by molecular weight, but refuted the idea of octaves. It was capable of accommodating the s-block (groups 1A and 2A), the p-block (groups 3A to 8A), the d-block (transition metals), and the f-block (lanthanoids and actinoids). In anticipation of the discovery of more elements, Mendeleev left several empty spaces in the table; for instance, he predicted the discovery of two elements with mass between 65 and 75 amu and a third element with mass between 40 and 50 amu.
30. Several of the atomic mass calculations were inaccurate during the time that periodicity was first discovered. Which of the following pairs of elements were NOT arranged correctly by mass on Newlands’s table?
A. Gold and platinum
B. Manganese and iron
C. Yttrium and indium
D. Tantalum and tungsten
31. Which of the following most strongly discredits the accuracy of the law of octaves?
A. The discovery of all of the naturally occurring elements in the s-block and the p-block.
B. The discovery of most of the naturally occurring elements in the d-block and the f-block.
C. J. J. Thomson’s discovery of the electron.
D. Ernest Rutherford’s discovery of the nucleus.
32. Mendeleev’s table was modified several times after its initial publication. Which of the following findings did NOT require modification of the existing entries in the table?
I. A unique element is characterized by a specific number of protons.
II. Electrons are arranged in orbitals and energy levels.
III. The atomic mass of gallium is approximately 70 amu.
A. II only
B. III only
C. II and III only
D. I, II, and III
33. Assuming that all known elements at the time were accounted for in Newlands table of elements, which of the following had NOT been discovered when Newlands published his table?
A. f-block elements
D. Noble gases
34. Mendeleev predicted the existence of an element with atomic mass of 44. If his prediction were correct, which of the following properties would it exhibit?
A. Its atomic radius would be larger than calcium’s atomic radius.
B. Its ionic radius would be larger than calcium’s atomic radius.
C. It would lose an electron less readily than calcium would.
D. It would accept an electron less readily than calcium would.
35. What element on Newlands’ table had the largest atomic radius?
36. Which of the following, if true, would MOST strengthen the claim that Newlands should be credited as the inventor of the modern periodic table?
A. Although most scientists dismissed Newlands’ theory, it was widely accepted within his home country of England.
B. Mendeleev approved of Newlands’ work upon reading about it a few years after he formulated his own periodic table.
C. Mendeleev created his version of the periodic table in an attempt to refute Newlands’ theory.
D. Newlands created a refined version of his system that was similar to Mendeleev’s table, but failed to publish it before Mendeleev.
PASSAGE V (QUESTIONS 37–44)
A student inserts a sliding divider into a simple cylinder to perform a series of three experiments with an unknown gas. The gas exhibits ideal behavior. Before each experiment, the divider is reset so that V1 = V2 and the contents are at STP. The total volume of the cylinder is 2 L. The student’s cylinder apparatus is illustrated below:
The student increases the temperature of the gas in V1 to 45°C while keeping the temperature of V2 constant.
The student uses mechanical force to move the central divider in the cylinder such that 3 V1 = V2. The temperature of the gas and the cylinder remains constant throughout this experiment.
The student releases half of the molar contents of V2, and does not change the molar contents of V1.
While these experiments are being performed in near-ideal conditions (can be assumed to be ideal), an equation was derived in 1873 by Johannes van der Waals to account for the nonideal behavior of gases:
37. In Experiment 1, what is the final volume of 1 mol of gas in V1?
A. 164R L
B. 318R L
C. 358R L
D. 403R L
38. Which of the following graphs MOST accurately illustrates the relationship between volume (V) and temperature (T) in experiment 1, assuming isobaric conditions?
39. In experiment 2, what is the final pressure of the gas with volume V1?
A. 0.5 atm
B. 1.5 atm
C. 2 atm
D. 3 atm
40. In the van der Waals equation for nonideal gas behavior, a corrects for
A. intermolecular repulsive forces.
B. the volume of the molecules themselves.
C. minute changes in atmospheric pressures.
D. intermolecular attractive forces.
41. What is the temperature of 64 g of pure O2 gas in a 3 atm, 2 L environment?
A. 1.5/R K
B. 2/R K
C. 3/R K
D. 6/R K
42. The student removes the partition, creating a cylinder with V = 2 L. If there are 0.5 mol CO2(g), 1.5 mol NO(g), and 1 mol Cl2(g), in the cylinder, what is the partial pressure of the NO(g) at 300 K?
A. 115R atm
B. 225R atm
C. 375R atm
D. 450R atm
43. Under which of the following conditions do the contents of V1 behave most like an ideal gas?
A. High temperature, low pressure
B. Low volume, high pressure
C. Low temperature, high volume
D. Low temperature, high pressure
44. Which of the following is the most likely result of experiment 3 after re-equilibration with the new molar concentrations?
A. V1 will expand and V2 will shrink.
B. P2 will be greater than P1.
C. Neither V nor P will change because they are unrelated to molar concentration.
D. P1 will be greater than P2.
PASSAGE VI (QUESTIONS 45–52)
Patients often use antacids to counteract potential adverse effects caused by an excess of stomach acid. Most antacids are weak bases whose primary function is to neutralize the hydrochloric acid in the stomach. Because of their simplicity, a wide variety of such drugs is available on the market; however, some are more effective than others. The drug typically reacts with the antacid to produce a conjugate acid and a conjugate base, as in the following examples:
Mg(OH)2(s) + HCl(aq) MgCl2(aq) + H2O(1)
Al2(CO3)3(s) + 6HCl(aq) 2AlCl3(aq) + 3H2CO3 (aq)
A student attempted to test the efficacy of various antacids by adding 1 gram of each drug to a beaker containing 100 mL of 0.1 M HCl. He noticed that stronger antacids tend to leave larger precipitates, so he determined that the strength of an antacid could be estimated by measuring the mass of the precipitate after complete neutralization and comparing it with the molecular weight of the reactant. His results were fairly accurate for magnesium salts, aluminum salts, and calcium salts (Group A); however, they disagreed with published results for sodium salts and potassium salts (Group B).
After inspecting the student’s experimental setup, the professor pointed out a flaw in the student’s reasoning. The student then decided to redesign his experiment; in the second setup, he chemically combined various quantities of antacid along with a standard amount of HCl and measured the pH of the resulting solutions. This time, he determined that an HCl sample was completely neutralized when its pH was equal to 7. The “overall efficacy” of each antacid was quantified as the number of moles of HCl that can be neutralized by one gram of antacid.
45. Which of the following does NOT describe reaction 1?
A. Double-displacement reaction
B. Neutralization reaction
C. Oxidation-reduction reaction
D. Acid-base reaction
46. What is the approximate percent composition of the cation in the conjugate base of the acid from reaction 1?
A. 10% B. 25% C. 75% D. 90%
47. If the student tested each of the following antacids, which would yield the greatest overall efficacy?
48. Which of the following is TRUE about NaHCO3 in the following reaction?
NaHCO3(s) + HCl(aq) NaCl(aq) + H2CO3(aq)
A. Because one of the products of the reaction is an acid, NaHCO3 does not function as an antacid.
B. Because one of the products of the reaction is a weaker acid than HCl, NaHCO3 is capable of raising the pH of the stomach but cannot neutralize the acid completely.
C. Because H2CO3 decomposes into H2O(1) and CO2(g), NaHCO3 is an effective antacid.
D. Because H2CO3 decomposes into H2O(1) and CO2(g), NaHCO3 is capable of raising the pH of the stomach but cannot neutralize the acid completely.
49. Antacid AX reacts with HCl to yield a mixture with a pH of 5.4 according to the equation below. What is the limiting reagent?
AX(s) + HCl(aq) ACl(aq) + HX(aq)
C. Conjugate base of HCl
D. Conjugate acid of antacid
50. When the student tested magnesium hydroxide with his first experimental setup, approximately how much antacid remained at the end of the reaction?
A. 750 mg
B. 500 mg
C. 200 mg
D. 300 mg
51. The student noticed that stronger antacids often leave larger precipitates when they are present as an excess reagent because a stronger antacid
A. neutralizes more acid, which subsequently produces a larger precipitate.
B. produces more product, which subsequently appears in the precipitate.
C. requires more of the reactant, so higher quantities of unreacted material are usually present in the precipitate.
D. requires less of the reactant, so higher quantities of unreacted material are usually present in the precipitate.
52. Which of the following BEST explains why the student’s initial results were correct for group A but incorrect for group B?
A. Group A contains very strong bases, while group B contains slightly weaker bases.
B. Group A contains compounds that dissociate into multiple ions, while group B contains compounds that dissociate into only two ions.
C. Group A contains compounds with insignificant solubility, while group B contains compounds with considerable solubility.
D. Group A contains cations with a + 2 or +3 oxidation state, while group B contains cations with a +1 oxidation state.