AP Chemistry Unit 3 Test Review

AP Chemistry Unit 3 Test Review Topics Covered: Gases Liquids & Solids Kinetics

1) The density of an unknown gas is 4.20 grams per liter at 3.00 atmospheres pressure and 127 °C. What is the molecular weight of this gas? (R = 0.0821 liter-atm / mole-K) (A) 14.6 (B) 46.0 (C) 88.0 (D) 94.1 (E) 138 2) Two flexible containers for Gas are at the same temperature and pressure. One holds 0.50 gram of hydrogen and the other holds 8.0 grams of oxygen. Which of the following statements regarding these gas samples is FALSE? (A) The volume of the hydrogen container is the same as the volume of the oxygen container. (B) The number of molecules in the hydrogen container is the same as the number of molecules in the oxygen container. (C) The density of the hydrogen sample is less than that of the oxygen sample. (D) The average kinetic energy of the hydrogen molecules is the same as the average kinetic energy of the oxygen molecules. (E) The average speed of the hydrogen molecules is the same as the average speed of the oxygen molecules. 3) 3 Ag(s) + 4 HNO3 <===> 3 AgNO3 + NO(g) + 2 H2O The reaction of silver metal and dilute nitric acid proceeds according to the equation above. If 0.10 mole of powdered silver is added to 10. milliliters of 6.0-molar nitric acid, the number of moles of NO gas that can be formed is (A) 0.015 mole (B) 0.020 mole (C) 0.030 mole (D) 0.045 mole (E) 0.090 mole 4) A sample of 0.010 mole of oxygen gas is confined at 127 °C and 0.80 atmosphere in a 1.0 L flask. What would be the pressure of this sample at 27 °C and the same volume? (A) 0.10 atm (B) 0.20 atm (C) 0.60 atm (D) 0.80 atm (E) 1.1 atm 5) A sample of 3.0 grams of an ideal gas at 121 °C and 1.5 atmosphere pressure has a volume of 1.0 Iiters. Which of the following expressions is correct for the molar mass of the gas? The ideal gas constant, R, is 0.08 (L-atm) / (mole K). (A) [(0.08)(400)] / [(3.0)(1.0)(1.5)] (B) [(l.O)(l.5)] / [(3.0)(0.08)(400)] (C) [(O.O8)(1.0)(1.5)] / [(3.0)(400)] (D) [(3.0)(0.08)(400)] / [(1.0)(1.5)] (E) [(3.0)(0.08)(1.5)] / (1.0)(400)] 6) Samples of F2 gas and Xe gas are mixed in a container of fixed volume. The initial partial pressure of the F2 gas is 8.0 atmospheres and that of the Xe gas is 1.7 atmospheres. When all of the Xe gas reacted, forming a solid compound, the pressure of the unreacted F2 gas was 4.6 atmospheres. The temperature remained constant. What is the formula of the compound? (A) XeF (B) XeF3 (C) XeF4 (D) XeF6 (E) XeF8 7) A rigid metal tank contains oxygen gas. Which of the following applies to the gas in the tank when additional oxygen is added at constant temperature? (A) The volume of the gas increase. (B) The pressure of the gas decreases. (C) The average speed of the gas molecules remains th same. (D) The total number of gas molecules remains the same. (E) The average distance between the gas molecules increases. 8) Equal numbers of moles of He(g), Ar(g), and Ne(g) are placed in a glass vessel at room temperature. If the vessel has a pinhole-sized leak, which of the following will be true regarding the relative values of the partial pressures of the Gas remaining in the vessel after some of the gas mixture has effused? A) PHe < PNe < PAr B) PHe < PAr < PNe C) PNe < PAr < PHe D) PAr < PHe < PNe E) PHe = PAr = PNe 9) Which of the following Gas deviates most from ideal behavior? A) SO2 B) Ne C) CH4 D) N2 E) H2

10) The structural isomers C2H5OH and CH3OCH3 would be expected to have the same values for which of the following? (Assume ideal behavior.) (A) Gaseous densities at the same temperature and pressure (B) Vapor pressures at the same temperature (C) Boiling points (D) Melting points (E) Heats of vaporization 11) X = CH3-CH2-CH2-CH2-CH3 Y = CH3-CH2-CH2-CH2-OH Z = HO-CH2-CH2-CH2-OH Based on concepts of polarity and hydrogen bonding, which of the following sequences correctly lists the compounds above in the order of their increasing solubility in water? (A) Z < Y < X (B) Y < Z < X (C) Y < X < Z (D) X < Z < Y (E) X < Y < Z 12) On a mountaintop, it is observed that water boils at 90°C, not at 100°C as at sea level. This phenomenon occurs because on the mountaintop the

A) equilibrium water vapor pressure is higher due to the higher atmospheric pressure B) equilibrium water vapor pressure is lower due to the higher atmospheric pressure C) equilibrium water vapor pressure equals the atmospheric pressure at a lower temperature D) water molecules have a higher average kinetic energy due to the lower atmospheric pressure E) water contains a greater concentration of dissolved Gas

13) Under which of the following conditions of temperature and pressure will H2 gas be expected to behave most like an ideal gas?

(A) 50 K and 0.10 atm (B) 50 K and 5.0 atm (C) 500 K and 0.10 atm (D) 500 K and 50 atm

The volume of a sample of air in a cylinder with a movable piston is 2.0 L at a pressure P1, as shown in the diagram above. The volume is increased to 5.0 L as the temperature is held constant. The pressure of the air in the cylinder is now P2.

What effect do the volume and pressure changes have on the average kinetic energy of the molecules in the sample?

(A) The average kinetic energy increases. (B) The average kinetic energy decreases. (C) The average kinetic energy stays the same. (D) It cannot be determined how the kinetic energy is affected without knowing P1 and P2. Questions 15-17 refer to the following.

The table below contains information about samples of four different gases at 273 K. The samples are in four identical rigid containers numbered 1 through 4.

Containe Gas Pressur Mass of r e Sample (g) (atm) 1 He 2.00 ? 2 Ne 2.00 ? 3 ? 2.00 16.0

4 SO2 1.96 64.1

15) On the basis of the data provided above, the gas in container 3 could be

(A) CH4 (B) O2 (C) Ar (D) CO2

16) Under the conditions given, consider containers 1, 2, and 4 only. The average speed of the gas particles is

(A) greatest in container 1 (B) greatest in container 2 (C) greatest in container 4 (D) the same in containers 1, 2, and 4

17) The best explanation for the lower pressure in container 4 is that SO2 molecules

(A) have a larger average speed than the other three gases (B) occupy a larger portion of the container volume than the other three gases (C) have stronger intermolecular attractions than the other three gases (D) contain pi bonds, while the other gases contain only sigma bonds 18) Name Structural Formula Molar Mass (g/mol) Acetone 58.1

1-propanol 60.1

Butane 58.1

The table above shows the structural formulas and molar masses for three different compounds. Which of the following is a list of the compounds in order of increasing boiling points? (A) Butane < 1-propanol < acetone (B) Butane < acetone < 1-propanol (C) 1-propanol < acetone < butane (D) Acetone = butane < 1-propanol

19. 2 A(g) + B(g) <===> 2 C(g) When the concentration of substance B in the reaction above is doubled, all other factors being held constant, it is found that the rate of the reaction remains unchanged. The most probable explanation for this observation is that

(A) the order of the reaction with respect to substance B is 1 (B) substance B is not involved in any of the steps in the mechanism of the reaction (C) substance B is not involved in the rate-determining step of the mechanism, but is involved in subsequent steps (D) substance B is probably a catalyst, and as such, its effect on the rate of the reaction does not depend on its concentration (E) the reactant with the smallest coefficient in the balanced equation Genlly has little or no effecton the rate of the reaction

20. rate = k[X] For the reaction whose rate law is given above, a plot of which of the following is a straight line? (A) [X] versus time (B) log [X] versus time (C) 1/[X] versus time (D) [X] versus 1/time (E) log [X] versus 1/time

Initial Initial Rate of Initial [O ] 21. The initial-rate data in the table above were Experiment [NO] 2 Formation of NO (mol L¯1 2 obtained for the reaction represented below. (mol L¯1 (mol L¯1 s¯1) What is the experimental rate la for the reaction? 1 0.10 0.10 2.5 x 10¯4 (A) rate = k[NO] [O2] (B) rate = k[NO] [O2]2 2 0.20 0.10 5.0 x 10¯4 (C) rate = k[NO]2 [O2] 3 0.20 0.40 8.0 x 10¯3 (D) rate = k[NO]2 [O2]2 (E) rate = k[NO] / [O2] X2 + Y2  X2Y2 rate = k [X2] 22. A reaction and its experimentally determined rate law are represented above. A chemist proposes two different possible mechanisms for the reaction, which are given below:

Mechanism 1 Mechanism 2 X2  2X (slow) X2  2X (slow) X + Y2  XY2 (fast) X + Y2  XY + Y (fast) X + XY  X2Y2 (fast) X + XY  X2Y (fast) X2Y + Y  X2Y2 (fast)

Based on the information above, which of the following is true? (A)Only mechanism 1 is consistent with the rate law and valid. (B) Only mechanism 2 is consistent with the rate law and valid. (C) Both mechanism 1 and mechanism 2 are consistent with the rate law and valid (D)Neither mechanism 1 nor mechanism 2 is consistent with the rate law nor valid.

- + 2+ 5H2O2(aq) + 2MnO4 (aq) + 6H (aq)  2Mn (aq) + 8H2O (l) + 5O2 (g)

- In a titration experiment, H2O2 (aq) reacts with aqueous MnO4 (aq) as represented by the equation above. The dark purple KMNO4 solution is added from a buret to a colorless, acidified solution of H2O2 (aq) in an Erlenmeyer flask. (Note: At the end point of the titration, the solution is a pale pink color.)

-1 -3 23. At a certain time during the experiment, the rate of disappearance of MnO4 (aq) was 2.0 x 10 mol/L s. What was the rate of appearance of O2 at the same time? (A) 2.5 x 10-3 mol/L s (B) 5.0 x 10-3 mol/L s (C) 2.0 x 10-3 mol/L s (D) 1.6 x 10-3 mol/L s

24. Consider the reaction represented by the equation 2B + 2A  B2A2. During a reaction in which a large excess of reactant B was present, the concentration of reaction A was monitored over time. A plot of the natural logarithm of the concentration of A versus time is shown in the figure above. The order of the reaction with respect to reactant A is (A) zero order (B) first order (C) second order (D) third order NO (g) + NO3 (g)  2NO2 (g) rate = k[NO][NO3] 25. The reaction represented above occurs in a single step that involves a collision between a particle of NO and a particle of NO3. A scientist correctly calculates the rate of collisions between NO and NO3 that have sufficient energy to overcome the activation energy. The observed reaction rate is only a small fraction of the calculated collision rate. Which of the following best explains the discrepancy? (A) The energy of collisions between two reactant particles is frequently absorbed by collision with a third particle. (B) The two reactant particles must collide with a particular orientation in order to react. (C) The activation energy for a reaction is dependent on the concentrations of the reactant particles. (D) The activation energy for a reaction is dependent on temperature.

Part II: Free Response (~50%) Long Response: Calculator may be used. CLEARLY SHOW THE METHOD USED AND STEPS INVOLVED IN ARRIVING AT YOUR ANSWERS. It is to your advantage to do this, because you may earn partial credit if you do and you will receive little or no credit if you do not. Attention should be paid to significant figures. Be sure to write all your answers to the questions on the lined pages following each question in this booklet.

1. A student collected a sample of hydrogen gas by the displacement of water as shown by the diagram above. The relevant data are given in the following table.

GAS SAMPLE DATA Volume of sample 90.0 mL Temperature 25 C Atmospheric Pressure 745 mm Hg Equilibrium Vapor Pressure 23.8 mm Hg o of H2O (25 C) (a) Calculate the number of moles of hydrogen gas collected.

(b) Calculate the number of molecules of water vapor in the sample of gas.

(c) Calculate the ratio of the average speed of the hydrogen molecules to the average speed of the water vapor molecules in the sample.

(d) Which of the two gases, H2 or H2O, deviates more from ideal behavior? Explain your answer.

2. CaCO3 (s)  CaO (s) + CO2 (g)

When heated, calcium carbonate decomposes according to the equation above. In a study of the decomposition of calcium carbonate, a student added a 50.0 gram sample of powdered, solid CaCO3 to a 1.00L rigid container. The student sealed the container, pumped out all the gases, then heated the container in an oven at 1100 K. As the container was heated, the total pressure of CO2 gas in the container was measured over time. The final pressure in the container is 1.04 atm.

The student repeated the experiment, but this time the student used 100.0 g sample of powdered solid CaCO3. In this experiment, the final pressure in the container was 1.04 atm, which was the same final pressure as in the first experiment.

(a)Calculate the number of moles of CO2 gas present in the container when the final pressure was measured. (b)The student claimed that the final pressure in the container in each experiment became constant because all of the solid CaCO3 had decomposed. Based on the data, do you agree with this claim? Explain.

3. Nitrogen monoxide gas, a product of the reaction above, can react with oxygen to produce nitrogen dioxide gas, as represented below. 2 NO(g) + O2(g)  2 NO2(g)

Initial Concentration of Initial Concentration of O2 Initial Rate of Formation Experiment -1 -1 -1 -l NO (mol L ) (mol L ) of NO2 (mol L s )

1 0.0200 0.0300 8.52  10-2 2 0.0200 0.0900 2.56  10-1 3 0.0600 0.0300 7.67  10-1

(d) Determine the order of the reaction with respect to each of the following reactants. Give details of your reasoning, clearly explaining or showing how you arrived at your answers. (i) NO

(ii) O2 (e) Write the expression for the rate law for the reaction as determined from the experimental data.

(f) Determine the value of the rate constant for the reaction, clearly indicating the units.

4. The following mechanism has been proposed for the reaction of methane gas with chlorine gas. All species are in the gas phase. Step 1 Cl2  2 Cl fast equilibrium

Step 2 CH4 + Cl  CH3 + HCl slow

Step 3 CH3 + Cl2  CH3Cl + Cl fast

Step 4 CH3Cl + Cl  CH2Cl2 + H fast Step 5 H + Cl  HCl fast

(d) In the mechanism, is CH3Cl a catalyst, or is it an intermediate? Justify your answer.

(e) Identify the order of the reaction with respect to the CH4(g), according to the mechanism. Justify your answer.

Short Response: No calculator maybe used. For each of the following three reactions, in part (i) write a balanced equation for the reaction and in part (ii) answer the question about the reaction. In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. 5. Explain each of the following in terms of atomic and molecular structures and/or intermolecular forces. Account for each of the following observations about pairs of substances. In your answers, use appropriate principles of chemical bonding and/or intermolecular forces. In each part, your answer must include references to both substances.

(a) Even though NH3 and CH4 have similar molecular masses, NH3 has a much higher normal boiling point

(-33C) than CH4 (-164C).

(b) At 25C and 1.0 atm, ethane (C2H6) is a gas and hexane (C6H14) is a liquid.

(c) Si melts at a much higher temperature (1,410C) than Cl2 (-101C). (d) MgO melts at a much higher temperature (2,852C) than NaF (993C).

Equations Practice: (a) A 0.1M solution of ammonium chloride is mixed with a 0.1M solution of potassium hydroxide. (i) Balanced equation:

(ii) What evidence of a reaction will be observed? Explain.

(b) Carbon dioxide is bubbled into water. (i) Balanced equation:

(ii) Will the resulting product have a pH < 7, pH > 7, or pH = 7? Explain.

(c) Water is electrolyzed. (i) Balanced equation:

(ii) Is this a chemical or physical change? Explain.