Study Guide
Field 104: Chemistry
Sample Selected-Response Questions
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General Test Directions
This test contains two sections: (1) a section with selected-response questions and (2) a constructed-response section. The directions for the constructed-response assignment appear before that section.
Each question in the first section is a selected-response question with four answer choices. Read each question and answer choice carefully and choose the start uppercase ONE end uppercase best answer. Try to answer all questions. In general, if you have some knowledge about a question, it is better to try to answer it. You will start uppercase NOT end uppercase be penalized for guessing.
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You may work on and complete the selected-response questions and the constructed-response assignment in any order that you choose. Be sure to allocate your time carefully so that you are able to complete the entire test within the testing session.
Use of any other type of calculator or outside reference materials during the testing session is prohibited.
Sample Selected-Response Questions
Competency 0001
Understand the structure of the atom.
1. Use the table of isotope masses below to answer the question that follows.
| Isotope | Relative atomic mass |
|---|---|
| chlorine-35 | 35.0 A M U |
| chlorine-37 | 37.0 A M U |
Elemental chlorine has an average atomic mass of 35.5 A M U. It is made up of two chlorine isotopes shown in the table. What is the approximate natural abundance of chlorine-35?
- 25.0%
- 50.0%
- 75.0%
- 100.0%
Correct Response: C. This question requires the examinee to demonstrate the ability to estimate the percent abundance of an isotope of an element by analyzing the relative atomic mass of the isotopes of a sample of that element and the average atomic mass of the element. Since there are only two isotopes present in this sample of chlorine, C L 35 and C L 37, and the average atomic mass of this chlorine sample is 35.5 A M U, the approximate natural abundance of C L 35 would have to be closest to 75% out of the answer choices provided. If the answer was 50% then the average mass would be 36.0 A M U, and if it were 100% it would be 35.0 A M U. So, the only answer choice that would put the average atomic mass between 35.0 and 36.0 A M U would be 75%.
Competency 0002
Understand the properties of substances and the patterns in those properties.
2. Isopropyl alcohol, C 3 H 8 O, has been used to reduce fevers by applying it to skin. This is no longer recommended due to the risk of skin or lung irritation. Which of the following reasons best explains why isopropyl alcohol can cool skin more quickly than water of the same temperature?
- Isopropyl alcohol's hydrogen bonds are weaker than water's, making it easier for the alcohol to evaporate from the skin.
- Isopropyl alcohol's dispersion forces are stronger, and, due to this, heat can be wicked away more easily.
- Water has a higher surface tension due to stronger IMFs, so it beads up more on the skin.
- Water can create ion dipole attraction with ions present on the skin's surface.
Correct Response: A. This question requires the examinee to demonstrate the ability to identify the types and strengths of intermolecular forces between molecules. The strongest intermolecular force that both isopropyl alcohol and water have between their molecules is hydrogen bonding. Since water has two hydrogens attached to a very polar oxygen atom, while isopropyl alcohol only has one, water has the ability to form hydrogen bonds in more places than isopropyl alcohol. This makes isopropyl alcohol's ability to hydrogen bond weaker than water's, and the weaker the intermolecular force, the easier it is for evaporation to occur. Evaporation is a cooling process and will wick heat away from the skin.
Competency 0003
Understand the formation and characteristics of chemical compounds.
3. Which of the following molecules is nonpolar?
- carbon monoxide
- nitrogen trifluoride
- phosphorus pentachloride
- sulfur dioxide
Correct Response: C. This question requires the examinee to demonstrate the ability to draw Lewis structures to identify molecular polarity based off a molecule's name. Phosphorus pentachloride has trigonal bipyramidal geometry with electrons being pulled 180 degrees in the axial position and 120 degrees in the equatorial position, causing dipoles to cancel. When dipoles cancel, the molecule is considered nonpolar.
Competency 0004
Understand the compositions and characteristics of elements, compounds, and mixtures.
4. Which of the following statements correctly identifies why calcium chloride is considered a compound?
- Calcium chloride is composed of atoms.
- Calcium chloride dissolves in water.
- Calcium chloride has a high melting point.
- Calcium chloride is made up of two different chemically bound elements.
Correct Response: D. This question requires the examinee to demonstrate the ability to identify compounds correctly. A compound is a substance that is made up of two or more different elements bonded together in simple whole number ratios. Calcium and chlorine are two different elements that are bonded in a 1:2 ratio. Physical properties do not distinguish between elements and compounds.
Competency 0005
Understand the formation and properties of various states of matter.
5. Use the table of isotope masses below to answer the question that follows.
Boiling Points of Hydrogen-Containing Compounds at 1 atmosphere Pressure
| Compound | Central Atom Period | Central Atom Group | Central Atom Atomic Number | Boiling Point (K) |
|---|---|---|---|---|
| C H 4 | 2 | 14 | 6 | 112 |
| N H 3 | 2 | 15 | 7 | 240 |
| H 2 O | 2 | 16 | 8 | 273 |
| H F | 2 | 17 | 9 | 293 |
| S I H 4 | 3 | 14 | 14 | 161 |
| P H 3 | 3 | 15 | 15 | 186 |
| H 2 S | 3 | 16 | 16 | 213 |
| H C L | 3 | 17 | 17 | 188 |
The boiling point of methane (C H 4) is lower than would be predicted by comparison to the other values in the table because:
- for groups 15to17, the period 2 compounds all have hydrogen bonding intermolecular forces, which are much stronger than the dipole-dipole or induced dipole-dipole interactions present in all the other compounds.
- for groups 15to17, the period 3 compounds all have hydrogen bonding intermolecular forces, which are much weaker than the dipole-dipole or induced dipole-dipole interactions present in all the other compounds.
- the molecules for the period 3 elements are larger for groups 15to17 than they are for period 2 elements, making the electron distance between molecules farther apart and the interactions weaker.
- the molecules for the period 3 elements are smaller for groups 15to17 than they are for period 2 elements, making the electron distance between molecules farther apart and the interactions weaker.
Correct Response: A. This question requires the examinee to demonstrate the ability to identify the types and strengths of the intermolecular forces that exist between the hydrogen-containing molecules in groups 15 to 17. Here, the examinee will analyze a data table for element location in the periodic table and each molecule’s boiling point. Methane is a nonpolar molecule that only contains London dispersion forces between its molecules, while the elements in groups 15 to 17 and period 2 create polar molecules with hydrogen that have the ability to hydrogen bond. None of the other molecules present in the data table have the ability to hydrogen bond, so they all have lower boiling points than those that can.
Competency 0006
Understand the characteristics of chemical reactions.
6. Which of the following chemical reactions will not take place?
- solid C U O H 2 plus 2 aqueous H C L produces aqueous C U C L 2 plus 2 liquid H 2 O
- solid C U C O 3 plus 2 aqueous H C L produces aqueous C U C L 2 plus 2 liquid H 2 O plus gaseous C O 2
- solid C U plus 2 aqueous H C L produces aqueous C U C L 2 plus gaseous H 2
- solid C U O plus 2 aqueous N H 4 C L produces aqueous C U C L 2 plus 2 gaseous N H 3 plus liquid H 2 O
Correct Response: C. This question requires the examinee to compare the relative activities of elements. Hydrogen is typically included in listed activity series of metals, even though it is a nonmetal. It falls roughly in the middle of the list. Copper is a very inactive metal, falling toward the bottom of the list. Given those relative positions, copper will not replace hydrogen as a cation in response C. In responses A and B, the copper compound acts as a base in a reaction with an acid. In response D, copper 2 oxide acts as a base to ammonium chloride's acid as they react.
Competency 0007
Understand the use of mass and particle number relationships to describe chemical reactions.
7. During a gravimetric analysis lab, one group of students calculated the theoretical yield of a precipitate as 5.0 grams. After performing the experiment, the group's actual yield was only 2.5 grams. Which of the following reasons most likely explains the group's 50% yield?
- They forgot to rinse the precipitate off their stirring rod and onto their filter paper before weighing.
- They allowed their precipitate to become contaminated by another insoluble solid in the lab.
- They massed their precipitate on the filter paper and forgot to subtract the weight of the filter paper.
- They massed their precipitate while it was still wet.
Correct Response: A. This question requires the examinee to demonstrate the ability to identify a common lab error that occurs during gravimetric analysis that would cause the yield of the precipitate to be less than expected. As precipitation occurs, students are usually asked to stir their mixture to speed up precipitation. Some students forget to rinse the precipitate formed off of their stirring rods and onto their filter paper, which would reduce the actual yield of their precipitate. Each of the other answer choices are errors that could occur during this lab, but each of those errors would result in a higher actual yield than their theoretical yield.
Competency 0008
Understand the kinetics of chemical reactions.
8. Hydrogen peroxide in a 3 percent aqueous solution is normally stored in a dark or opaque container to prevent ultraviolet light (U V) absorption. U V absorption accelerates the decomposition of hydrogen peroxide into oxygen and water according to the following equation.
2 H 2 O 2 yields 2 H 2 O plus O 2 in the presence of U V light
Which of the following statements best describes how UV absorption accelerates this decomposition?
- The U V light absorption causes the hydrogen peroxide molecules to coalesce, effectively increasing their concentration and therefore increasing the decomposition rate.
- The U V light absorbed by hydrogen peroxide is of sufficient energy to overcome the activation energy of the decomposition, increasing the rate of the decomposition reaction.
- The U V light absorbed by hydrogen peroxide catalyzes the decomposition reaction by reducing the activation energy and increasing the rate of decomposition.
- The U V absorption by the hydrogen peroxide causes the activation energy of the reaction to increase, resulting in an increased decomposition rate.
Correct Response: B. This question requires the examinee to demonstrate the ability to identify how radiation can speed up chemical reactions. U V light gives the reacting molecules additional energy to collide, causing successful collisions more quickly and speeding up the chemical reaction. Although U V light does speed up the decomposition of hydrogen peroxide by providing additional energy, it does not lower the activation energy open parens or give the molecule an alternate path of lower energy close parens.
Competency 0010
Understand energy changes in physical, chemical, and nuclear processes.
9. In a rigid isolated container, 1.0 mole of O 2 gas that is at 25degrees Celsius is mixed with 1.0 mole of N E gas that is at 10degrees Celsius. Which of the following statements correctly describes the change in the system?
- The average kinetic energy of the oxygen molecules increases with the addition of neon atoms.
- The final temperature of the system is bigger than 25degrees Celsius when the thermal equilibrium is established.
- The most probable speed of neon atoms increases as the system reaches thermal equilibrium.
- The direction of the heat flow is from neon atoms to oxygen molecules.
Correct Response: C. This question requires the examinee to demonstrate the ability to identify the direction of heat flow when substances at different temperatures are mixed, and associate thermal energy with the speed of gaseous atoms and molecules. When oxygen gas at 25 degrees Celsius is mixed with neon gas at 10 degrees Celsius, heat will travel from the warmer substance open parens oxygen close parens to the cooler substance open parens neon close parens. Neon's thermal energy will increase as the mixture reaches thermal equilibrium, increasing the speed of the neon atoms in the mixture.
Competency 0011
Understand the thermodynamics of physical and chemical processes.
10. Use the chemical equation below to answer the question that follows.
2 gaseous X Y plus gaseous Y 2 produces 2 gaseous X Y 2. Delta H equals positive 114 kilojoules.
Based on the thermodynamics of the reaction shown, the reaction can be said to be:
- spontaneous at all temperatures.
- spontaneous only at low temperatures.
- spontaneous only at high temperatures.
- nonspontaneous at all temperatures.
Correct Response: D. This question requires the examinee to demonstrate the ability to identify the spontaneity of a chemical reaction based off the entropy change, enthalpy change, and temperature during the reaction. In this synthesis reaction, 3 moles of gas are converted into 2 moles of gas, which indicates a decrease in the entropy of the reaction as it progresses. The enthalpy change, indicated by the value of delta H, is positive. This means that the reaction is endothermic. When entropy decreases and the reaction is endothermic, the reaction will be nonspontaneous at all temperatures. Examinees could use the Gibbs free energy equation, delta G equals delta H minus the product of T and delta S, to see that the change in Gibbs free energy will never be negative under these conditions.