Kaplan MCAT General Chemistry Review

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:

Reaction 1

Mg(OH)₂(s) + HCl(aq) MgCl₂(aq) + H₂O(1)

Reaction 2

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?

A. Al₂(CO₃)₃

B. Al(OH)₃

C. Al(HCO₃)₃

D. AlPO₄

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)

A. HCl

B. Antacid

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.