AP Chemistry 2015 #1-15

A 0.5 mol sample of He and a 0.5 mol sample of Ne are placed separately into two 10.0 L rigid containers at 25^oC. Each container has a pinhole opening. Which of the gases, He or Ne, will escape faster through the pinhole and why?

• He because the He atoms are moving at a higher average speed than the Ne atoms.

• Ne because its initial pressure in the container is higher

• Ne because the Ne atoms have a higher average kinetic energy than the He atoms

• Both gases will escape at the same rate because the atoms of both gases have the same average kinetic enery

The lattice energy of a salt is related to the energy required to separate the ions. For which of the following pairs of ions is the energy that is required to separate the ions largest?

• Na⁺ and Cl^-

• Cs⁺ and Br^-

• Mg²⁺ and O^2-

• Ca²⁺ and O^2-

The mass spectrum of element X is presented in the diagram shown. Based on the spectrum, which of the following can be concluded about element X?

• X is a transition metal and each peak represents an oxidation state of the metal

• X contains five electron sublevels

• The atomic mass of X is 90

• The atomic mass of X is between 90 and 92

Which of the following diagrams best depicts an alloy of Ni and B?

• A

• B

• C

• D

Which of the following is the strongest type of interaction that occurs between the atoms within the circled areas of the two molecules represented in the image?

• Polar Covalent Bond

• Nonpolar Covalent Bond

• Hydrogen Bond

• London Dispersion Forces

A hot iron ball is dropped into a 200.g sample of water initially at 50^oC. If 8.4 kJ of heat is transferred from the ball to the water, what is the final temperature of the water? The specific heat of water is 4.2 J/g^oC.

• 40 ^oC

• 51 ^oC

• 60 ^oC

• 70 ^oC

At 27^oC five identical rigid 2.0 L vessels are filled with N₂ and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO₃, NaBr, Cu, or I₂ as shown in the diagram. The volume taken up by the solids is negligible, and the initial pressure of N₂ in each vessel is 720 mmHg. All four vessels are heated to 127^oC and allowed to reach a constant pressure.

At 127^oC, the pressure in vessel 1 is found to be higher than that in vessel 2. Which of the following reactions best accounts for the observation?

• NaHCO₃(s) --> Na(s) + HCO₃(s)

• NaHCO₃(s) --> NaH(s) + CO₃(s)

• 2NaHCO₃(s) --> Na₂CO₃ (s) + CO₂(g) + H₂O(g)

• 2NaHCO₃(s) + N₂(g) --> 2NaNO₃(s) + C₂H₂(g)

At 27^oC five identical rigid 2.0 L vessels are filled with N₂ and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO₃, NaBr, Cu, or I₂ as shown in the diagram. The volume taken up by the solids is negligible, and the initial pressure of N₂in each vessel is 720 mmHg. All four vessels are heated to 127^oC and allowed to reach a constant pressure.

At 127^oC the entire sample of I₂ is observed to have vaporized. How does the mass of vessel 5 at 127^oC compare to its mass at 27^oC ?

• The mass is less, since I₂ is in the vapor phase

• The mass is the same, since the number of each type of atom in the vessel is constant.

• The mass is greater, since the I₂ will react with N₂ to form NI₃, which has a greater molar mass.

• The mass is greater, since the pressure is greater and the particles have a higher average kinetic energy.

At 27^oC five identical rigid 2.0 L vessels are filled with N₂ and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO₃, NaBr, Cu, or I_2. The volume taken up by the solids is negligible, and the initial pressure of N₂in each vessel is 720 mmHg. All four vessels are heated to 127^oC and allowed to reach a constant pressure.

The gas particles in the vessel 3 at 27^oC are represented in the diagram shown. The lengths of the arrows represent the speeds of the particles. Which of the following diagrams best represents the particles when vessel 3 is heated to 127^oC ?

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An acetate buffer solution is prepared by combining 50 mL of 0.20 M acetic acid, HC₂H₃O₂, and 50 mL of 0.20 M sodium acetate, NaC₂H₃O_2. A 5.0 mL sample of 0.10 M NaOH is added to the buffer solution. Which of the following is a correct pairing of the acetate species present in greater concentration and the pH of the solution after the NaOH is added? The pKa of acetic acid is 4.7.

• HC₂H₃O₂ , pH less than 4.7

• HC₂H₃O₂ , pH greater than 4.7

• C₂H₃O₂^- , pH less than 4.7

• C₂H₃O₂^- , pH greater than 4.7