2017 IPE Multiple Choice

If a pure sample of an oxide of sulfur contains 40. percent sulfur and 60. percent oxygen by mass, then the empirical formula of the oxide is (A) SO3 (B) SO4 (C) S2O6 (D) S2O8

(A) SO3

At 298 K and 1 atm, Br2 is a liquid with a high vapor pressure, and Cl2 is a gas. Those observations provide evidence that under the given conditions, the (A) forces among Br2 molecules are stronger than those among Cl2 molecules (B) forces among Cl2 molecules are stronger than the Cl−Cl bond (C) Br−Br bond is stronger than the Cl−Cl bond (D) Cl−Cl bond is stronger than the Br−Br bond

(A) forces among Br2 molecules are stronger than those among Cl2 molecules

When 5.0 g of NH4ClO4(s) is added to 100. mL of water in a calorimeter, the temperature of the solution formed decreases by 3.0°C. If 5.0 g of NH4ClO4(s) is added to 1000. mL of water in a calorimeter initially at 25.0°C, the final temperature of the solution will be approximately (A) 22.0°C (B) 24.7°C (C) 25.3°C (D) 28.0°C

(B) 24.7°C

The students determined that the reaction produced 0.010 mol of Cu(NO3)2 . Based on the measurement, what was the percent of Cu by mass in the original 2.00 g sample of the mixture? (A) 16% (B) 32% (C) 64% (D) 96%

(B) 32%

Which of the following statements best helps to explain why the contents of the tube containing the equilibrium mixture turned a lighter color when the tube was placed into an ice bath? (A) The forward reaction is exothermic. (B) The forward reaction is endothermic. (C) The ice bath lowered the activation energy. (D) The ice bath raised the activation energy.

(B) The forward reaction is endothermic.

When 4.0 L of He(g), 6.0 L of N2(g), and 10. L of Ar(g), all at 0°C and 1.0 atm, are pumped into an evacuated 8.0 L rigid container, the final pressure in the container at 0°C is (A) 0.5 atm (B) 1.0 atm (C) 2.5 atm (D) 4.0 atm

(C) 2.5 atm

The compound CCl4 is nonflammable and was once commonly used in fire extinguishers. On the basis of the periodic properties, which of the following compounds can most likely be used as a fire-resistant chemical? (A) BCl3 (B) CH4 (C) CBr4 (D) PbCl2

(C) CBr4

What effect will increasing [H+] at constant temperature have on the reaction represented above? (A) The activation energy of the reaction will increase. (B) The activation energy of the reaction will decrease. (C) The frequency of collisions between H+(aq) ions and ClO−(aq) ions will increase. (D) The value of the rate constant will increase.

(C) The frequency of collisions between H+(aq) ions and ClO−(aq) ions will increase.

The equilibrium system represented by the equation above initially contains equal concentrations of Cr2O7 and CrO4. Which of the following statements correctly predicts the result of adding a sample of 6.0 M NaOH(aq) to the system, and provides an explanation? (A) The mixture will become more orange because OH−(aq) will oxidize the Cr in CrO4. (B) The mixture will become more yellow because OH−(aq) will reduce the Cr in Cr2O7. (C) The mixture will become more yellow because OH−(aq) will shift the equilibrium toward products. (D) The color of the mixture will not change because OH−(aq) does not appear in the equilibrium expression.

(C) The mixture will become more yellow because OH−(aq) will shift the equilibrium toward products.

To determine the number of moles of Cu in the sample of the mixture, the students measured the absorbance of known concentrations of Cu(NO3)2(aq) using a spectrophotometer. A cuvette filled with some of the solution produced from the sample of the mixture was also tested. The data recorded by one student are shown in the table above. On the basis of the data provided, which of the following is a possible error that the student made? (A) The Cu(NO3)2(aq) from the sample of the mixture was not diluted properly. (B) The spectrophotometer was calibrated with tap water instead of distilled water. (C) The student labeled the cuvettes incorrectly, reversing the labels on two of the solutions of known concentration. (D) The spectrophotometer was originally set to an inappropriate wavelength, causing the absorbance to vary unpredictably.

(C) The student labeled the cuvettes incorrectly, reversing the labels on two of the solutions of known concentration.

In one student's experiment the reaction proceeded at a much slower rate than it did in the other students' experiments. Which of the following could explain the slower reaction rate? (A) In the student's sample the metal pieces were much smaller than those in the other students' samples. (B) The student heated the reaction mixture as the HNO3(aq) was added. (C) The student used a 1.5 M solution of HNO (aq) 3 instead of a 15.8 M solution of HNO3(aq). (D) The student used a 3.00 g sample of the mixture instead of the 2.00 g sample that was used by the other students.

(C) The student used a 1.5 M solution of HNO (aq) 3 instead of a 15.8 M solution of HNO3(aq).

A student prepares a solution by combining 100 mL of 0.30 M HNO2(aq) and 100 mL of 0.30 M KNO2(aq). Which of the following equations represents the reaction that best helps to explain why adding a few drops of 1.0 M HCl(aq) does not significantly change the pH of the solution? (A) K+(aq) + Cl−(aq) → KCl(s) (B) HNO2(aq) → H+(aq) + NO2 −(aq) (C) H+(aq) + OH−(aq) → H2O(l) (D) H+(aq) + NO2−(aq) → HNO2(aq)

(D) H+(aq) + NO2−(aq) → HNO2(aq)

Based on the diagram above, which of the following best helps to explain why MgO(s) is not able to conduct electricity, but MgO(l) is a good conductor of electricity? (A) MgO(s) does not contain free electrons, but MgO(l) contains free electrons that can flow. (B) MgO(s) contains no water, but MgO(l) contains water that can conduct electricity. (C) MgO(s) consists of separate Mg2+ ions and O2− ions, but MgO(l) contains MgO molecules that can conduct electricity. (D) MgO(s) consists of separate Mg2+ ions and O2− ions held in a fixed lattice, but in MgO(l) the ions are free to move and conduct electricity.

(D) MgO(s) consists of separate Mg2+ ions and O2− ions held in a fixed lattice, but in MgO(l) the ions are free to move and conduct electricity.

The ideal gas law best describes the properties of which of the following gases at 0°C and 1 atm? (A) PH3 (B) HBr (C) SO2 (D) N2

(D) N2

On the basis of molecular structure and bond polarity, which of the following compounds is most likely to have the greatest solubility in water? (A) CH4 (B) CCl4 (C) NH3 (D) PH3

(D) PH3

A student is given a sample of a pure, white crystalline substance. Which of the following would be most useful in providing data to determine if the substance is an ionic compound? (A) Examining the crystals of the substance under a microscope (B) Determining the density of the substance (C) Testing the electrical conductivity of the crystals (D) Testing the electrical conductivity of an aqueous solution of the substance

(D) Testing the electrical conductivity of an aqueous solution of the substance

The table above provides some information about two types of steel, both of which are alloys of iron and carbon. Which of the following best helps to explain why high-carbon steel is more rigid than low-carbon steel? (A) Elemental carbon is harder than elemental iron. (B) The additional carbon atoms within the alloy make the high-carbon steel less dense. (C) The additional carbon atoms within the alloy increase the thermal conductivity of the high-carbon steel. (D) The additional carbon atoms within the alloy make it more difficult for the iron atoms to slide past one another.

(D) The additional carbon atoms within the alloy make it more difficult for the iron atoms to slide past one another.

When H2(g) and O2(g) are mixed together in a rigid reaction vessel at 25°C, no reaction occurs. When the mixture is sparked, however, the gases react vigorously according to the equation above, releasing heat. Which of the following statements correctly explains why the spark is needed for the reaction to occur when the gases are originally at 25°C? (A) The reaction is not thermodynamically favorable at 25°C. (B) ΔH° for the reaction has a large positive value at 25°C. (C) ΔS° for the reaction has a large negative value at 25°C. (D) The reaction has a large activation energy at 25°C.

(D) The reaction has a large activation energy at 25°C.

A sample of a solid labeled as NaCl may be impure. A student analyzes the sample and determines that it contains 75 percent chlorine by mass. Pure NaCl(s) contains 61 percent chlorine by mass. Which of the following statements is consistent with the data? (A) The sample contains only NaCl(s). (B) The sample contains NaCl(s) and NaI(s). (C) The sample contains NaCl(s) and KCl(s). (D) The sample contains NaCl(s) and LiCl(s).

(D) The sample contains NaCl(s) and LiCl(s).

Which of the following statements identifies the greatest single reason that the value of Kp for the overall reaction at 298 K has such a large magnitude? (A) The activation energy for step 1 of the mechanism is large and positive. (B) The activation energy for step 2 of the mechanism is small and positive. (C) The value of ΔS° for the overall reaction is small and positive. (D) The value of ΔH° for the overall reaction is large and negative.

(D) The value of ΔH° for the overall reaction is large and negative.

The exothermic process represented above is best classified as a (A) physical change because a new phase appears in the products (B) physical change because O2(g) that was dissolved comes out of solution (C) chemical change because entropy increases as the process proceeds (D) chemical change because covalent bonds are broken and new covalent bonds are formed

(D) chemical change because covalent bonds are broken and new covalent bonds are formed