AP Chemistry DPM 2019

At 27 ℃, five identical rigid 2.0 L vessels are filled with N2(g) and sealed. Four of the five vessels also contain a 0.050 mol sample of NaHCO3 (S), NaBr(s), Cu(s), or I2(s), as shown in the diagram above. The volume taken up by the solids is negligible, and the initial pressure of N2(g) in each vessel is 720 mmHg. All four vessels are heated to 127 ℃ and allowed to reach a constant pressure. 1) At 127 ℃, 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? 2) At 127 ℃, the entire sample of I2 is observed to have vaporized. How does the mass of vessel 5 at 127℃ compare to its mass at 27℃? 3) The gas particles in vessel 3 at 27 ℃ are represented in the diagram above. The lengths of the arrows represent the speeds of the particles. Which of the following diagrams best represents the particles which vessel 3 is heated to 127℃?

1) 2NaHCO3(s) -> Na2CO3(s) + CO2(g) +H2O(g) 2) The mass is the same since the number of each type of atom in the vessel is constant. 3) Refer to 2015 question 9

The O2(g) produced from the decomposition of the 1.0 L sample of H2O2(aq) is collected in a previously evacuated 10.0 L flask at 300 K. What is the approximate pressure in the flask after 400 s?

1.2 atm

Which of the following is the balanced net ionic equation for the reaction between Li(s) and water?

2Li(aq) + 2H2O(l) -> 2 Li+(aq) +2OH-(aq) +H2(g)

On the basis of the pH curve, the pKa value of the acid is closest to

5

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

60 ℃

An acetate buffer solution is prepared by combining 50 mL of 0.20 M acetic acid, HC2H3O2(aq), and 50 mL 0f 0.20 M sodium acetate, NaC2H3O2(aq). A 5.0 mL sample of 0.10 M NaOH(aq) is added to the buffer solution. Which of the following is a correct pairing of the acetate species present in greater concentration and of the pH solution after the NaOH is added? (the pKa of acetic acid is 4.7)

Acetate Species: C2H3O2 - pH: >4.7

To gravimetrically analyze the silver content of a piece of jewelry made from an alloy of Ag and Cu a student dissolves a small preweighed sample in hno3, ag+ (aq) and cu2+(aq) ions form in the solution. Which of the following should be the next step in the analytical process?

Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions.

Which of the following accounts for the observation that the pH of pure water at 37 ℃ is 6.8?

At 37 ℃ the auto-ionization constant for water, Kw, is larger than it is at 25 ℃

The first five ionization energies of a second period element are listed in the table above. Which of the following correctly identifies the element and best explains the data in the table

B (boron), because it has three valence electrons

The molecular formula and molar mass of two straight chain hydrocarbons are listed in the table above. Based on the information in the table, which compound has the higher boiling point and why is that compound's boiling point higher?

C4H10, because it has more electrons, resulting in greater polarizability and stronger dispersion forces.

A sample of a compound that contains only the elements C, H, and N is completely burned in O2 to produce 44.0 g of CO2, 45g of H2O, and some NO2. A possible empirical formula of the compound is

CH5N

The exothermic dissolution of Mg(OH)2 (s) in water is represented by the equation above. The Ksp of Mg(OH)2 is 1.8 x 10⁻¹¹. Which of the following changes will increase the solubility of Mg(OH)2 in an aqueous solution?

Decreasing the pH

Which of the following best depicts an alloy of Ni and B? (I couldn't upload a picture, but this is question 4 from the 2015 exam. Answer: A)

Explanation of answer: Alloys are made when two metals are melted together and re-solidified. Completely random arrangement of atoms, but generally, one of the element's atoms will fall into the interstitial places between the solid form of the other element

Assume the bond enthalpies of the oxygen - hydrogen bonds in H2O are not significantly different from those in H2O2. Based on the value of ΔH° of the reaction, which of the following could be the bond enthalpies for the bonds broken and formed in the reaction?

H2O2: 150 O2: 500 O-H: 500

A 0.5 mole sample of He(g) and a 0.5 mole sample of Ne(g) are placed separately in two 10.0 L rigid containers at 25 ℃. Each container has a pinhole opening. Which of the gases, He(g) or Ne(g), will escape faster through the pinhole and why?

He(g) will escape faster because the He(g) atoms are moving at a higher average speed than the Ne(g) atoms.

Which of the following is the strongest type of interaction that occurs between the atoms within the circled areas of the two molecules represented above? (The picture shows H and O circled as well as H and N)

Hydrogen bond

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 the largest? (Assume that the distance between the ions in each pair is equal to the sum of the ionic radii.)

Mg2+ (g) and O2- (g)

The decomposition of H2O2(aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H2O2(aq) at a constant temperature of 300 K and recorded the concentration of H2O2 as a function of time. The results are given in the table below. Which of the following identifies the element(s) being oxidized and reduced in teh reaction?

Oxygen is both oxidized and reduced

A solution is prepared by mixing 50 mL of 1 M NaH2PO4 with 50 mL of 1 M Na2HPO4. On the basis of the information above, which of the following species is present in the solution at the lowest concentration?

PO43-

Acid dissociation constants of two acids are listed in the table above. A 20 mL sample of a 0.10 mL sample of a 0.10 M solution of each acid is titrated to the equivalence point with 20 mL of 0.10 M NaOH. Which of the following is a true statement about the pH of the solutions at the equivalence point?

Solution 1 has a higher pH at the equivalence point because CH3CO2H has a stronger conjugate base.

What will be the effect on the amount of gas produced if the experiment is repeated using 0.35g of K(s) instead of 0.35 g of Li(s)

Some gas will be produced but less than the amount of gas produced with Li(S)

Benzene, C6H6, has the structure shown above. Considering the observation that benzene is only sparingly soluble in water, which of the following best described the intermolecular forces of attraction between water and benzene?

The are dipole-induced dipole and London dispersion interactions between water and benzene.

The mass spectrum of element X is presented in the diagram above. Based on the spectrum, which of the following can be concluded about element X? (I couldn't upload a picture from the exam, but this is question 3 from the 2015 test)

The atomic mass of X is between 90 and 92

A 1.0 g sample of a cashew was burned in a calorimeter containing 1000. g of water, and the temperature of the water changed from 20.0°C to 25.0°C. In another experiment, a 3.0 g sample of a marshmallow was burned in a calorimeter containing 2000. g of water and the temperature of the water changed from 25.0°C to 30.0°C. Based on the data, which of the following can be concluded about the energy content of 1.0 g of each of the two substances.

The combustion of 1.0 g of cashew releases more energy than the combustion of 1.0 g of marshmallow.

The reaction between NO(g) and O2(g) to produce NO2(g) in a rigid reaction vessel is represented in the diagram above. The pressure inside the container is recorded using a pressure gauge. Which of the following statements correctly predicts the change in pressure as the reaction goes to completion at constant temperature, and provided the correct explanation?

The pressure will decrease because there are fewer molecules of product than of reactants.

Which of the following statements is a correct interpretation of the data regarding how the order of the reaction can be determined?

The reaction is first order if the plot of ln[H2O2] versus time is a straight line

A certain gas, XY(g), decomposes as represented in the equation above. A sample of each of the three gases is put in a previously evacuated container. The initial partial pressures of the gases are shown in the table below. The temperature of the reaction mixture is held constant. In which direction will the reaction proceed?

The reaction will form more reactant.

The heating curve for a sample of pure ethanol is provided above. The temperature was recorded as a 50.0 g sample of solid ethanol was heated at a constant rate. Which of the following explains why the slope of segment T is greater than the slope of segment R?

The specific heat capacity of the gaseous ethanol is less than the specific heat capacity of liquid ethanol.

Which of the following changes will most likely increase the rate of reaction between Li(s) and water?

Using a 0.35 g sample of Li(s) cut into small pieces

The reaction is thermodynamically favorable. The signs of ΔG° and ΔS° for the reaction are which of the following?

ΔG°: negative ΔS° : positive