Pre test Chem

COMPETENCY 010 23 23. Of the following solutions, which has the lowest freezing point? A. 0.5 m CaCl2(aq) B. 0.5 m NaCl(aq) C. 0.5 m NaNO3(aq) D. 0.5 m HCl(aq

Option A is correct because 0.50 m CaCl2 dissociates into 3 ions in solution (CaCl2 →Ca2+ + 2 Cl− ), and the number of particles in solution is proportional to the freezing point depression. Option B is incorrect because 0.50 m NaCl dissociates into 2 ions in solution (NaCl → Na+ + Cl− ) and has fewer particles in solution than 0.50 m CaCl2. Hence, its freezing point depression is less than that of 0.50 m CaCl2. Option C is incorrect because 0.50 m NaNO3 dissociates into 2 ions in solution (NaNO3 → Na+ + NO3 − ) and has fewer particles in solution than does 0.50 m CaCl2. Hence, its freezing point depression is less than that of 0.50 m CaCl2. Option D is incorrect because 0.50 m HCl dissociates into 2 ions in solution (HCl → H+ + Cl−) and has fewer particles in solution than does 0.50 m CaCl2. Hence, its freezing point depression is less than that of 0.50 m CaCl2.

COMPETENCY 012 27 A + 2 B → 2 C 27. For the reaction represented above, the initial reaction rate is determined using initial concentrations: [A] = 1 M, [B] = 1 M, and [C] = 0. When the reaction is run again using initial concentrations: [A] = 1 M, [B] = 2 M, and [C] = 0, the initial reaction rate was found to have doubled. Based on the data, which of the following could be the initial rate law? A. Rate = [A][B] B. Rate = [A][B]2 C. Rate = [A]2[B]2 D.

Option A is correct because for the initial rate law Rate = [A][B], the initial reaction rate doubles when [B] doubles, calculated as follows: 2 2 1 1 Rate 2 [A] [B] (1 M) (2 M) × ×2 Rate 1 [A] [B] (1 M) (1 M) = = = . Option B is incorrect because for the initial rate law Rate = [A][B]2, the initial reaction rate increases fourfold when [B] doubles, calculated as follows: 2 2 2 2 2 2 1 1 Rate 2 [A] [B] (1 M) (2 M) × ×4 Rate 1 [A] [B] (1 M) (1 M) = = = . Option C is incorrect because for the initial rate law Rate = [A]2[B]2, the initial reaction rate increases fourfold when [B] doubles, calculated as follows: 2 2 2 2 2 2 22 2 2 1 1 Rate 2 [A] [B] (1 M) (2 M) × ×4 Rate 1 [A] [B] (1 M) (1 M) = = = . Option D is incorrect because for the initial rate law Rate = 2 2 [A][B] [C] , again the initial reaction rate increases fourfold when [B] doubles, due to the [B]2 term in the rate law

COMPETENCY 005 10 10. Of the following, which is an example of a physical change only? A. Snow sublimating in the Arctic B. An iron nail rusting C. A candle burning D. A lead storage battery recharging

Option A is correct because snow (H2O) changes state from solid to gas, which is a physical change, and no chemical changes occur. Option B is incorrect because Fe in the iron nail reacts with O2 to form FeO2, which is a chemical change. Option C is incorrect because a candlewick reacts with oxygen in the flame, and a combustion reaction occurs, which is a chemical change. Option D is incorrect because recharging a lead storage battery involves an electrochemical reaction.

COMPETENCY 012 29 A2(g) + 2 B2(g) 2 B2A(g) 29. Which of the following is the expression for the equilibrium constant, in terms of concentration, for the equilibrium represented above? A. = 2 2 2 22 [B A] [A ][B ]cK B. = 2 22 2 2 [A ][B ] [B A]cK C. = 2 2 2 22 [2 B A] [A ][2 B ]cK D. = 2 22 2 2 [A ][2 B ] [2 B A

Option A is correct because the equilibrium constant expression should have the concentration of the product in the numerator, raised to the power that corresponds to the coefficient for the product in the balanced equation (in this case the coefficient is 2). And the concentrations of the reactants should be in the denominator, each raised to the power that corresponds to the coefficient for that reactant in the balanced equation (in this case the coefficients are 1 for A2 and 2 for B2. Options B, C, and D are incorrect.

COMPETENCY 014 34 34. If 5.00 amperes are provided for 10.0 hours in an electroplating experiment, which of the following is the maximum amount of Cu2+ that can be plated out of 3.00 L of a 2.00 M CuSO4 solution? (Assume F = 96,500 C/mol.) A. 0.933 mol Cu B. 1.87 mol Cu C. 3.73 mol Cu D. 6.00 mol Cu

Option A is correct because the maximum amount of copper that can be plated out, based on the current provided, is 0.933 mol Cu, calculated as follows: 5 amperes = 5 Coulombs/second 5 C/s = and 5 C 60 min 60 s 10 hr 180,000 C s 1 hr 1 min ×× × = and 1 mol e 180,000 C 1.865 mol e 96,500 C − − × = and 2 1 mol Cu 1.865 mol e 0.933 mol Cu 2 mol e + − − × = . Option B is incorrect because 1.87 mol of Cu is twice the amount that is produced and does not account for the fact that 2 moles of electrons are needed to plate out 1 mole of Cu. Option C is incorrect because 3.73 mol is four times the amount that is produced. Option D is incorrect because 6.00 mol of Cu is far larger than the amount that can be produced and is equal to all of the Cu that is contained in the 3.00 L solution.

37. Which of the following activities is most appropriate after a short lesson on the significance of oxidation numbers? A. The students attempt to balance a simple redox reaction B. The teacher presents a demonstration involving a combustion reaction C. The students perform an acid-base titration in the lab D. The students determine the number of neutrons in one atom of iodine-131 based on information from the periodic table

Option A is correct because the oxidation number of the elements in the various species in the reaction must be known in order to correctly balance a redox (oxidation-reduction) reaction. In addition to trying to balance the number of atoms on both sides of the equation, the students must also balance the increase and decrease in oxidation numbers that take place, and various species gain or lose electrons. Option B is incorrect because although a combustion reaction may involve an oxidation and reduction, the demonstration would not illustrate the use of oxidation numbers. Option C is incorrect because an acid-base titration may or may not involve an oxidation-reduction, but the titration would not illustrate the use of oxidation numbers. Option D is incorrect because the number of neutrons in iodine-131 can be deduced by finding the atomic number of iodine on the periodic table. The oxidation state of iodine is not related to this determination.

COMPETENCY 009 20 20. Which of the following is the balanced equation for the displacement reaction of potassium with aluminum nitrate? A. 3 K + Al(NO3)3 → 3 KNO3 + Al B. K + AlNO3 → KNO3 + Al C. 3 K + AlNO3 → K3N + AlO3 D. K + AlN → KN + A

Option A is correct because the reaction of potassium with aluminum nitrate forms KNO3 and Al, the formula for aluminum nitrate is Al(NO3)3, the formula for potassium nitrate is KNO3 and the equation is balanced with an equal number of each type of atom on the right and left sides of the equation (i.e., three K atoms, one Al atom, three N atoms, and nine O atoms). Option B is incorrect because the formula for aluminum nitrate is not correctly represented. Option C is incorrect because the incorrect products are formed, and the formula for aluminum nitrate is not correctly represented. Option D is incorrect because the incorrect products are formed, and the compound formulas are not correctly represented.

COMPETENCY 003 6 6. Which of the following is an example of a model? A. The equation PV = nRT. B. A liquid has a green color. C. Chemistry is a vital part of biology. D. When 12 g of carbon completely reacted with oxygen, it formed 44 grams of carbon dioxide.

Option A is correct because the equation represents a mathematical model of the behavior of an ideal gas in which intermolecular attractions and gas particle volume are accounted for. Option B is incorrect because the color of the liquid is an observation. Option C is incorrect because although chemistry is very much a part of biology, this fact does not represent a model. Option D is incorrect because the quantitative analysis of the carbon reaction is an observation based on analysis of data and does not represent a model.

16. A gas sample at 300.0 K and 1.0 atm is allowed to expand into an adjoining vessel until the volume is doubled. The gas is then heated, causing the temperature to increase to 900.0 K. What is the final pressure of the gas sample? A. 1.0 atm 1.0 atmosphere B. 1.5 atm 1.5 atmospheres C. 2.0 atm 2.0 atmospheres D. 6.0 atm 6.0 atmospheres

Option B is correct because pressure of a fixed number of moles of gas is inversely proportional to volume and directly proportional to temperature. =× × 1 2 2 1 2 1 V T P P V T . Hence,P2 = 1.5 atm, calculated as follows: = ×× = 2 1 900 K 1 atm 1.5 atm 2 300 K P . Option A is incorrect because pressure is not 1.0 atm. Option C is incorrect because pressure is not 2.0 atm. Option D is incorrect because pressure is not 6.0 atm.

COMPETENCY 004 9 9. Which of the following scientists is particularly noted for his or her contribution to radiochemistry? A. Robert Boyle B. Marie Curie C. Dmitri Mendeleev D. John Dalto

Option B is correct because Marie Curie did extensive work in isolating radioactive isotopes, and she discovered two radioactive elements. Option A is incorrect because Robert Boyle is most known for his discovery, Boyle's law, which indicates that the volume of a gas is inversely proportional to the absolute pressure of the gas if the temperature is kept constant in a closed system. Option C is incorrect because Dmitri Mendeleev is most known for the development of a periodic table. Option D is incorrect because John Dalton is most known for his atomic theory, which describes some basic principles of atoms and how they combine to form compounds, but it does not involve radioactivity.

COMPETENCY 004 8 8. Of the following, which contributes the most to water pollution in streams near mountains? A. Nuclear power plants B. Mine drainage C. Carbon dioxide emissions from gas-powered automobiles D. Oil-well drilling

Option B is correct because acid and metal ion mine-drainage from abandoned coal mines has a significant impact on many streams in mountainous coal-mining regions. Option A is incorrect because although nuclear power plants can contribute to thermal pollution, plants are typically located near rivers or oceans, not in mountain regions near streams. Radioactive emissions are not common and are not the major source of water pollution in mountain streams. Option C is incorrect because carbon dioxide emissions can lead to a minor amount of dissolved carbon dioxide (carbonic acid), but the level is not considered significant. Option D is incorrect because oilwell drilling is not typically done in areas that could affect streams in mountainous regions.

COMPETENCY 001 2 2. Which of the following is safety equipment that can be found in a high school chemistry lab? A. Bunsen burner B. Eyewash station C. Barometer D. Glass mercury thermometer

Option B is correct because an eyewash station is used to flush the eyes when liquids have been splashed or sprayed into a person's eyes. Option A is incorrect because a Bunsen burner is used to heat some materials in the lab and must be used with care. Option C is incorrect because a barometer is used to measure atmospheric pressure. Option D is incorrect because a glass mercury thermometer can pose a significant hazard due to possible broken glass and mercury exposure.

COMPETENCY 011 26 26. A 50.0 gram sample of a metal at 100.0°C is dropped into a beaker of 25.0°C water. The water warms up and the metal cools down. After thermal equilibrium was reached at 30.0°C, it was determined that 4,000.0 J of energy was absorbed by the water. What is the specific heat capacity of the metal? A. 1.75 J g-1 °C-1 B. 1.14 J g-1 °C-1 C. 0.875 J g-1 °C-1 D. 0.570 J g-1 °C-1

Option B is correct because the specific heat capacity of the metal is 1.14 J g-1 °C-1. The heat lost by the cooling metal is equal to the heat absorbed by the water and is found from − − = ° ° 4000 J 1 1 1.14 J g C . (50.0 g)(70.0 C) Options A, B, and C are incorrect.

7. A linear measurement of 156.020 mm is made. Which of the following is the best representation in scientific notation that indicates the correct number of significant figures? A. 1.56020 × 105 mm B. 1.56020 × 102 mm C. 1.5602 × 102 mm D. 1.56 × 102 mm

Option B is correct because the number 156.020 is represented by two powers of ten ( 2 10 ) and indicates six significant figures. Option A is incorrect because it incorrectly indicates five powers of ten ( 5 10 ), even though it does include all six significant figures. Option C is incorrect because although it correctly indicates two powers of ten ( 2 10 ), it does not include all six significant figures; it includes only five. Option D is incorrect because although it correctly indicates two powers of ten ( 2 10 ), it does not include all six significant figures; it includes only three

COMPETENCY 008 18 18. Which of the following molecules has trigonal planar geometry? A. NH3 B. H2O C. BH3 D. CO2

Option C is correct because the molecule BH3 has trigonal planar geometry due to having three bonding pairs but no electron pairs around the central atom (boron). Based on valence-shell-electron-pairrepulsion (VSEPR) theory, this configuration has the minimum repulsion. Option A is incorrect because the NH3 molecule has trigonal pyramidal geometry. Option B is incorrect because the molecule H2O has bent geometry. Option D is incorrect because the molecule CO2 has linear geometry.

COMPETENCY 013 32 32. A 1 M aqueous solution of an acid HA with pH = 6.0 is titrated with a 0.1 M NaOH solution. If the pH = 10.0 at the equivalence point, which of the following is most likely true about the acid HA? A. HA is a strong acid B. HA is a weak acid C. HA is a strong electrolyte D. HA is chemically inert

Option B is correct because when a weak acid is titrated by a strong base such as NaOH, the equivalence point is not at pH = 7.0, but instead will be in the basic range (in this case, pH = 10.0). This is explained by the hydrolysis of the salt that forms, NaA. Because A− is a conjugate base of a weak acid, it will react with water to form some HA and OH− (A− + H2O HA + OH−). The pH at the equivalence point will be related to the Ka of the acid. Option A is incorrect because HA is not a strong acid, as indicated by the pH at the equivalence point. Option C is incorrect because HA is a weak acid, as indicated by the pH at the equivalence point. Hence, it cannot be a strong electrolyte because weak acids are those that do not dissociate completely in water. Strong electrolytes are compounds that completely dissociate into ions in solution. Option D is incorrect because HA is reacting with the NaOH during the titration, as evidenced by the change in pH from 6.0 to 10.0. Hence, it is not chemically inert.

COMPETENCY 002 5 5. Students conducted an activity to determine the acidity of several liquid products commonly used in homes. They added several drops of red cabbage juice to samples of the substances and recorded the resulting colors. The activity is best described as which of the following? A. Statistical analysis B. Forensic analysis C. Descriptive study D. Synthesis experiment

Option C is correct because a descriptive study indicates characteristics, not causes. Option A is incorrect because no numerical data were collected. Option B is incorrect because only observations were recorded and no analysis was done. Option D is incorrect because no synthesis reactions took place

COMPETENCY 015 35 35. Which of the following nuclear processes is an example of an alpha emission? A. 215Bi → 215Po B. 240U → 240Np C. 222Rn → 218Po D. 40K → 40Ar

Option C is correct because an alpha particle is emitted in the process: 222Rn → 218Po. ( ) 222 218 4 86Rn Po He → + 84 2 Option A is incorrect because a negative beta emission is taking place in which an electron is emitted in the process: 215Bi → 215Po. ( ) 215 215 0 83Bi Po → + 84 −1e Option B is incorrect because a negative beta emission is taking place in which an electron is emitted in the process: 240U → 240Np. ( ) 240 240 0 92U Np → + 93 −1e Option D is incorrect because a positive beta emission is taking place in which a positron is emitted in the process: 40K → 40Ar. ( )

COMPETENCY 010 25 25

Option C is correct because energy is released (exothermic) when the gaseous water molecules come together to form solid H2O in a crystal structure (frost). The potential energy is higher when the molecules are far apart in the gaseous state, and the potential energy is reduced when the molecules are close together in the solid state. Option A is incorrect because the input of energy is required (endothermic) to break a bond between carbon atoms. Option B is incorrect because the input of energy is required (endothermic) to change liquid water to gaseous water in which the molecules are much farther apart (higher potential energy). Option D is incorrect because the removal of an electron from sodium to form an ion requires the input of energy (endothermic).

17. Which of the following compounds has predominately covalent bonding? A. CaCl2 B. AlCl3 C. CH2Cl2 D. Na2O

Option C is correct because in CH2Cl2 molecules both the C- H and the C- Cl bonds are covalent. Option A is incorrect because the compound CaCl2 has ionic bonding between metallic Ca2+ ions and nonmetallic Cl− ions. Option B is incorrect because the compound AlCl3 has ionic bonding between metallic Al3+ ions and nonmetallic Cl− ions. Option D is incorrect because the compound Na2O has ionic bonding between metallic Na+ ions and nonmetallic O2− ions

COMPETENCY 016 38 38. Which of the following is an element of inquiry-based science instruction? A. A teacher-led question and answer session B. A video presentation of science principles to be included in a unit of study C. A student forming a hypothesis prior to a lab activity D. A student writing a report after researching information on the Interne

Option C is correct because inquirybased learning does involve students proposing a hypothesis prior to designing an experiment to test the hypothesis. Option A is incorrect because a teacher asking questions is important, but it is not an element of inquiry-based science instruction. Option B is incorrect because videos can be helpful, but they are not elements of inquiry-based learning. Option D is incorrect because writing reports can have value, but it is not an element of inquiry-based learning.

COMPETENCY 006 13. 13 Which of the following is the ground-state electron configuration for Se? A. 1s2 2s22p6 3s23p6 4s24p4 B. 1s2 2s22p6 3s23p6 4s24p6 5s25p6 C. 1s2 2s22p6 3s23p63d10 4s24p4 D. 1s2 2s22p6 3s23p6 4s24p44d1

Option C is correct because it contains the correct number of electrons and correctly indicates the electron configuration according to the Aufbau principle. Option A is incorrect because it contains 24 electrons, whereas Se has 34 electrons. Option B is incorrect because it contains the correct number of electrons, but it is missing the 3d electrons. Option D is incorrect because it contains the correct number of electrons, but it has 4d electrons, not 3d electrons.

COMPETENCY 009 21 2 C2H6(g) + 7 O2(g) → 4 CO2(g) + 6 H2O(g) 21. According to the balanced equation above, what is the maximum mass of CO2 that can be produced if 3.00 mol of C2H6(g) and 160.0 g of oxygen are available? A. 2.86 g B. 6.00 g C. 126 g D. 264 g

Option C is correct because the mass that is produced is 126 g. The oxygen is the limiting reagent. 160 g oxygen is 5 moles of O2. Based on the balanced equation, 5 moles of O2 can completely react with 1.42 moles of C2H6. 2 6 2 2 6 2 2 C H 5 O 1.42 mol C H 7 O × = . So the 3 moles of C2H6 is in excess. Hence, the maximum mass of CO2 that can be produced is 126 g (to three significant figures), calculated as follows: 2 2 2 2 2 2 4 mol CO 44 g CO 5 mol O 126 g CO 7 mol O 1 mol CO × ×= . Option A is incorrect because 2.86 is the number of moles of CO2 produced, not the mass produced. Option B is incorrect because 6.0 is neither the number of moles nor the mass of the product produced. Option D is incorrect because 264 is the mass of CO2 that would be produced if all the C2H6 was consumed, but there is insufficient oxygen to do that

. COMPETENCY 001 1 1. The volume of a liquid sample can be measured and reported as 18.00 mL by using which of the following pieces of glassware? A. 25 mL graduated cylinder B. 25 mL beaker C. 50 mL buret D. 50 mL Erlenmeyer flask

Option C is correct because the smallest divisions on a scale of a 50 mL buret are typically 0.1 mL. Thus, the volume of the sample can be estimated to two decimal places: 18.00 ± 0.01 mL. Option A is incorrect because the smallest divisions on a scale of a 25 mL graduated cylinder are typically 1 mL. Thus, the volume of the sample can be estimated to one decimal place only: 18.0 ± 0.1 mL. Option B is incorrect because the smallest divisions on a scale of a 25 mL beaker are 5 mL or greater. Thus, the volume of the sample can be estimated to be between 15 and 20 mL. Option D is incorrect because the smallest divisions on a scale of a 50 mL Erlenmeyer flask are typically 10 mL. Thus, the volume of the sample can be estimated to be between 10 and 20 mL.

COMPETENCY 006 12 12. Based on the periodic table, which of the following atoms has the highest first ionization energy? A. Ca B. Ni C. Br D. I

Option C is correct because, based on periodic trends, the first-ionization energy increases from left to right in a row on the periodic table and decreases from top to bottom of a column. Br is farther to the right than Ni and Ca in a row and is above I in a column. Option A is incorrect because on the periodic table Ca is farther to the left on a row than Br. Option B is incorrect because on the periodic table Ni is farther to the left on a row than Br. Option D is incorrect because on the periodic table I is below Br in a column.

COMPETENCY 010 22 22. If 23.8 g of MgCl2 is completely dissolved in water, forming a 500.0 mL solution, which of the following is the concentration of Cl− in the solution? (Assume molar mass of MgCl2 is 95.2 g.) A. 0.050 M B. 0.250 M C. 0.500 M D. 1.00 M

Option D is correct because concentration of Cl− is 1.0 M, calculated as follows: Since 500 mL = 0.5 L, then 2 2 2 2 23.8 g MgCl 1 mol MgCl 2 Cl 1.0 M 0.5 L 95.2 g MgCl 1 MgCl − × ×= the fraction. Option A is incorrect because 0.050 does not correctly give the concentration of Cl− expressed in mol/L; it is the approximate concentration of MgCl2 expressed in g/mL. Option B is incorrect because 0.250 does not correctly give the concentration of Cl− expressed in mol/L; it is the total number of moles of MgCl2 dissolved. Option C is incorrect because 0.500 does not correctly give the concentration of Cl− expressed in mol/L; it is the number of moles of MgCl2 per liter

COMPETENCY 010 24 24. Which of the following actions will change the solubility of a solid compound in water? A. Stirring the water vigorously B. Using a powder solid rather than a chunk solid C. Adding more water D. Changing the temperature of the water

Option D is correct because solubility is defined as the maximum mass of a solid that can dissolve in 100 mL of a solution at a particular temperature. Changing the temperature will increase or decrease the solubility (maximum mass that can dissolve in 100 mL). Option A is incorrect because stirring only increases the rate of dissolving and has no effect on the solubility (maximum mass that can dissolve in 100 mL). Option B is incorrect because using powder instead of chunks only increases the rate of dissolving and has no effect on the solubility (maximum mass that can dissolve in 100 mL). Option C is incorrect because adding water can increase the total mass that dissolves, but it has no effect on the solubility (maximum mass that can dissolve in 100 mL). The maximum possible concentration of the solution is the same.

COMPETENCY 012 28 aE RTk Ae − = 28. For some chemical reactions, the rate constant follows the Arrhenius expression, given above. What does the Ea term represent in the Arrhenius expression? A. The change in enthalpy for the reaction B. The change in Gibbs energy for the reaction C. The change in entropy for the reaction D. The activation energy for the reaction

Option D is correct because Ea represents the activation energy. Option A is incorrect because Ea does not represent the change in enthalpy for the reaction rxn ( ) ∆H . Option B is incorrect because Ea does not represent the change in Gibbs energy for the reaction rxn ( ) ∆G . Option C is incorrect because Ea does not represent the change in entropy for the reaction rxn ( ) ∆S .

COMPETENCY 013 30 30. Which of the following mixtures will form a buffer solution? A. 50 mL of 0.01 M KCl(aq) and 50 mL of 0.01 M KOH(aq) B. 50 mL of 0.01 M KCl(aq) and 50 mL of 0.01 M HCl(aq) C. 50 mL of 0.01 M KOH(aq) and 50 mL of 0.01 M HCl(aq)l D. 50 mL of 0.01 M CH3COOH(aq) and 50 mL of 0.01 M CH3COOK(aq)

Option D is correct because a 1:1 mixture of a weak acid (CH3COOH) and the salt of a weak acid (CH3COOK) will form a buffer solution. There is an equilibrium involving the CH3COOH and the CH3COO−. Small additions of either acid or base will not result in a pH change based on the equilibrium. Option A is incorrect because a mixture of a neutral salt (KCl) and a strong base (KOH) will not form a buffer solution. Option B is incorrect because a mixture of a neutral salt (KCl) and a strong acid (HCl) will not form a buffer solution. Option C is incorrect because a mixture of a strong base (KOH) and a strong acid (HCl) will not form a buffer solution.

COMPETENCY 002 4 4. Of the following, which is most appropriate to do after forming a hypothesis? A. Organize data B. Draw conclusions C. Propose a theory D. Test the hypothesis

Option D is correct because a hypothesis must be tested in order to support or disprove it. Option A is incorrect because the testing data have not yet been produced, and any preliminary observational data available should have been organized and analyzed in the process of developing a hypothesis. Option B is incorrect because the hypothesis has not yet been tested, so there are not sufficient data for analyzing and drawing conclusions. Option C is incorrect because a theory cannot be developed until enough testing has been done to produce data that support the hypothesis.

COMPETENCY 017 39 39. Of the following, which is the most appropriate way to assess a student's understanding of preparing a 1 M HCl solution from a 6 M HCl solution? A. Short quiz B. Lab report C. Summative assessment D. Performance assessment

Option D is correct because an assessment of the students preparing the solution in the lab is the best way to assess their understanding of the theory, their implementation of the theory and their technique. This approach is called a performance assessment. Option A is incorrect because a short quiz would assess only some theoretical understanding of how to prepare solutions by dilution, but it will not assess the students' ability to implement the theory or their technique. Option B is incorrect because a report can assess only how well students explain what should be done, but it will not assess their ability to implement the theory or their technique. Option C is incorrect because a summative assessment will assess only some theoretical understanding of how to prepare solutions by dilution, but it will not assess students' ability to implement the theory or their technique.

COMPETENCY 007 15 15. When the temperature increases in a sample of gas molecules in a closed container of fixed volume, which of the following changes takes place? A. A decrease in the frequency of collisions between molecules B. An increase in the volume of each molecule C. An increase in the average attractive forces between molecules D. An increase in the average speed of the molecules

Option D is correct because as temperature increases, the average speed of the molecules in the sample will increase. Option A is incorrect because the frequency of collisions will increase, not decrease. Option B is incorrect because the actual volume of each molecule does not change with temperature. Option C is incorrect because the attractive forces are dependent on the electrostatic nature of the molecules and the distance between the molecules. As temperature increases, the electrostatic properties of each molecule do not change, and the sample is in a fixed-volume container, so the average distance between molecules will not change. Hence, there is no change in the average attractive forces between molecules.

COMPETENCY 005 11 11. Which of the following is true about elements? A. When a chemical reaction takes place, the particles in the nucleus of the atoms are rearranged. B. Isotopes are different forms of an element in which the atoms have a different number of protons. C. All atoms of the element carbon have the same mass. D. Compounds consist of two or more different kinds of elements.

Option D is correct because compounds are composed of two or more elements. Option A is incorrect because chemical reactions do not involve changes in the nucleus. Option B is incorrect because isotopes of an element have the same number of protons but a different number of neutrons. Option C is incorrect because carbon has isotopes that have atoms with a different number of neutrons and hence a different mass even though they have the same number of protons and electrons. For example, all carbon atoms have 6 protons and 6 electrons, but carbon-12 has 6 neutrons and carbon-13 has 7 neutrons

COMPETENCY 014 33 AgNO3(aq) + NaCl(s) AgCl(s) + Na+(aq) + NO3−(aq) 33. Which of the following is true about the reaction represented above? A. Silver is reduced. B. Sodium is oxidized. C. Chlorine is reduced. D. No oxidation or reduction is taking place in the reaction.

Option D is correct because none of the species have a change in oxidation state during the reaction; no oxidation or reduction is taking place. Option A is incorrect because silver has an oxidation state of +1 in both reactants and products; hence, is not being reduced. Option B is incorrect because sodium has an oxidation state of +1 in both reactants and products; hence, is not being oxidized. Option C is incorrect because chlorine has an oxidation state of −1 in both reactants and products; hence, is not being reduced.

31 NOTE: After clicking on a link, right click and select "Previous View" to go back to original text. COMPETENCY 013 31. What is the pH of 0.001 M NaOH(aq) at 298 K ? A. 1.0 B. 3.0 C. 8.0 D. 11.0

Option D is correct because pH = 11.0 for 0.001 M NaOH solution. For an aqueous solution, the pH is equal to −log[H+]. And at 298 K, 14 14 1 10 1 10 11 [H ] 1 10 M [OH ] (0.001) − − + − − × × = = = × . So pH = 11.0, based on the following calculation: since pH = - log[H+], then 11 pH= log(1 10 )= ( 11) 11.0 − − × −− = . Options A, B and C are incorrect.

COMPETENCY 001 3 3. A shipment of chemicals is delivered to a high school chemistry lab. Of the following, the most appropriate way to store the substances is to organize them by A. the alphabetical names of the substances. B. the concentrations of the solutions. C. solids or liquids. D. the chemical properties of the substances.

Option D is correct because substances that are stored near each other might react chemically with each other and create safety concerns. Options A, B, and C are incorrect because they are organizational concepts that are not as important as the possibility of chemical reactions between the various substances.

19. How many oxygen atoms are in 2.0 mol of NaNO3 ? A. 3 B. 6 C. 1.8 × 1024 D. 3.6 × 1024

Option D is correct because there are three oxygen atoms in the formula, there are 2 moles of the compound, and there is a total of 23 24 2 3 6.02 10 3.6 10 ×× × = × oxygen atoms. Option A is incorrect because there are three oxygen atoms in the formula but many more in 2.0 mol of NaNO3. Option B is incorrect because there are six oxygen atoms in two units of the formula but many more in 2.0 mol of NaNO3. Option C is incorrect because there are 24 1.8 10 × oxygen atoms in 1.0 mol of NaNO3, but there is twice that amount in 2.0 mol of NaNO3.

40. When teaching a complex unit it is important to frequently monitor and assess the students' understanding of the concepts throughout the unit by doing which of the following? A. Facilitating a class discussion while monitoring responses and questions B. Having students conduct frequent lab exercises with full lab reports C. Administering a series of short quizzes periodically throughout the unit D. Assigning a multistep research project that is due at the end of the unit

Options A and C are correct because they will effectively assess the students' understanding of the concepts throughout the unit. Option B is incorrect because frequent full lab reports will be timeconsuming and will assess much more than what is needed. Option D is incorrect because the feedback to the teacher will not be available until the end of the unit and will not provide the frequent monitoring of understanding that was desired.

COMPETENCY 015 36 36. The half-life of a radioactive isotope of hydrogen is 12.3 years. If the original sample of the isotope is 16 micrograms, which TWO of the following statements are true after 25 years elapse? A. A little more than 8.0 micrograms of the isotope will remain. B. A little less than 4.0 micrograms of the isotope will remain. C. More than two half-lives have elapsed. D. Although radioactive decay occurred, the mass of the isotope will still be 16 micrograms.

Options B and C are correct because after 25 years, the mass of the isotope that will remain is 3.9 micrograms, which is a little less than 4.0 micrograms. Since the half-life is 12.3 years, 25 years is more than two half-lives. If only two half-lives had elapsed (24.6 years), then the mass of isotope remaining would have been 4.0 micrograms: × × 1 1 16 micrograms = 4 micrograms. 2 2 The actual mass remaining after 25 years elapse can be calculated using the following steps. Based on the half-life, the decay rate constant can be found from − = 0.693 . 12.3 years kt Based on first-order decay kinetics, the amount of isotope remaining (x) is found from =− = × ln 0.693 25 years. ln16 micrograms 12.3 years x kt Solving this equation for x yields 3.9 micrograms of isotope remaining. Options A and D are incorrect.