Kaplan MCAT General Chemistry Review

B. Alkaline earth metals are less dense because their nuclei contain fewer neutrons.

C. Alkali metals are less dense because they contain fewer orbitals.

D. Alkali metals are less dense because they have a loosely bound electron in their outer shell.

43. Which of the following is NOT a correct characterization of the properties of halogens?

A. At room temperature, halogens naturally exist only in the gaseous and liquid states.

B. Halogens are highly likely to react with alkali metals.

C. Halogens can form stable ionic crystals with alkaline earth metals.

D. In their neutral form, halogens always have an outer shell of p⁵.

44. Which of the following contributes MOST to the malleability shown by transition elements?

A. Natural softness as compared to other metals

B. High electrical conductivity

C. Loosely held d-electrons

D. High melting points

45. Which of the following BEST explains why scientists closely examine metalloids when trying to find a biologic molecule to replace phosphorus?

A. Phosphorus is a metalloid.

B. Metalloids often behave as semiconductors.

C. Some metalloids exhibit similar bonding capabilities to phosphorus.

D. Metalloids exhibit flexibility in their properties so they can be manipulated easily.

PASSAGE VI (QUESTIONS 46–52)

Aerobic and anaerobic bacteria undergo different types of metabolism, and the properties of their metabolisms are unique. Some anaerobic bacteria are methane-producing bacteria. These bacteria have been studied to determine the relevance of their potential use in generating biological energy or biogas.

These methane-producing bacteria typically feed off of animal manure or other natural waste. In the process of utilizing animal waste, manure is collected from different types of animals including swine and cows. The manure is separated by phase and contains proteins, carbohydrates, and fats; bacteria then break down components into fatty acids.¹

Methanogens are the particular type of anaerobic bacteria that undertake the final steps of breaking down the fatty acids into simple products: methane and carbon dioxide. A common reactant is acetic acid, which breaks down according to the following reaction:

CH₃COOH CH₄ + CO₂

Other fatty acids can be used as substrates for these methane-generating reactions, including propionate and butyrate. Methanogenic bacteria can also convert carbon dioxide and hydrogen gas to form methane and water. At the end of this process, which typically takes place at 95° Celsius, methane can be used to generate energy as an alternative to fossil fuels.

46. What type of reaction is presented in the passage?

A. Combination reaction

B. Single-displacement reaction

C. Decomposition reaction

D. Combustion reaction

47. If the reaction begins with 120 grams of acetic acid, what is the theoretical yield, in grams, of methane?

A. 32.05 grams

B. 64.1 grams

C. 40.92 grams

D. 29.12 grams

48. What piece of evidence would support the passage’s argument that the decomposition of fatty acids can create energy serving as an alternative to fossil fuel?

A. Anaerobic bacteria can break down fatty acids efficiently at room temperature.

B. Methane gas can be compressed and transported.

C. The reaction generates gaseous products.

D. The reaction is exothermic.

49. What formula BEST demonstrates how to calculate the number of grams of acetic acid necessary to produce 88.02 grams of carbon dioxide?

50. One form of acetic acid, which is typically used as a salt, is called acetate. Sodium acetate can react with other chemical compounds in solution, an example of which is demonstrated below.

What is the correct net ionic equation for this reaction?

51. As described in the passage, methanogenic bacteria can utilize hydrogen gas to produce methane. At standard temperature and pressure, if there are 3 liters of hydrogen gas and 2 liters of carbon dioxide available to the bacteria, what would be the theoretical yield, in moles, of methane?

A. 0.134 moles

B. 0.0893 moles

C. 0.0335 moles

D. 0.536 moles

52. What is the percent yield if 8.02 g of methane is formed from the reaction of 50 liters of hydrogen gas, with excess carbon dioxide at standard temperature and pressure?

A. 43.1%

B. 14.4%

C. 89.6%

D. 64.7%

Practice Section 3

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. In 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 1–8)