Test Prep Test Prep Certifications OAT Questions & Answers

• Question 31:

  For the following nuclear reaction, fill in the correct daughter product.

  

  A. Option A

  B. Option B

  C. Option C

  D. Option D

  E. Option E

  Correct Answer: A

  Begin by looking at the reactant side and noting down the number of mass number and protons (235 and 92 respectively). These numbers have to match the total numbers on the product side. The 2 alpha-decay and 1 beta-decay give you a mass of 8, which means it is 227 short of the mass number in the reactants. They also produce a (2 + 2 − 1 = 3) number of protons, 89 short of balancing the reactant number of protons. Thus, your missing daughter nuclei will have a mass of 227 and 89 protons. Looking at a periodic table, the atom Ac has 89 protons.

• Question 32:

  

  In ideal gas circumstances, if the pressure and volume were both doubled. What would happen to the temperature?

  A. It would stay the same.

  B. It would half.

  C. It would double.

  D. It would quadruple.

  E. Cannot be calculated with this information.

  Correct Answer: D

  Ideal Gas Law: PV = nRT Doubling both the pressure and volume means you multiply the left side by a total of 4. Because temperature is proportional to this change, it will also quadruple.

• Question 33:

  The molar solubility of an hypothetical salt, AB, is 3.0 × 10−3. Find the Ksp

  A. 27 × 10−9

  B. 9 × 10−6

  C. 6 × 10−3

  D. 1.5 × 10−3

  E. 3.0 × 10−3

  Correct Answer: B

• Question 34:

  Which of the following is defined by the 2nd law of thermodynamics?

  A. In any spontaneous process, the entropy of the universe always increases.

  B. Energy cannot be created or destroyed.

  C. The entropy of a perfect crystal approaches 0 as temperature approaches absolute 0.

  D. Any object in motion will remain in motion unless a force is acted upon it.

  E. For every action, there is an equal and opposite reaction.

  Correct Answer: A

  Answer choice [Energy cannot be created or destroyed.] is the 1st law of thermodynamics and [The entropy of a perfect crystal approaches...] is the 3rd law. Choices [Any object in motion will remain in...] and [For every action, there is...] are part of Newton's laws of motion.

• Question 35:

  All of the following are characteristics of a galvanic cell EXCEPT:

  A. It is spontaneous.

  B. Anode is the site of oxidation.

  C. Anions flow to the anode via the salt bridge.

  D. The cathode is negative.

  E. All of the above are true.

  Correct Answer: D

  The cathode is positive in an galvanic cell. It is negative in a non-spontaneous electrolytic cell.

• Question 36:

  A reaction with a positive S and a positive H is spontaneous when?

  A. At all temperatures

  B. At high temperatures

  C. At low temperatures

  D. The reaction is not spontaneous at all.

  E. Not enough information is provided to complete this problem.

  Correct Answer: B

  A reaction with positive entropy and enthalpy means it is spontaneous at high temperatures (e.x. boiling). Whereas a reaction with both negative values for enthalpy and entropy means it is spontaneous at low temperatures only. A positive S and a negative H means the reaction is spontaneous at all temperatures, whereas the inverse (negative S and positive H) is not spontaneous at all temperatures.

• Question 37:

  A titration of NaOH and HF is made. Which of the following equivalence points pH can be possible?

  A. 7.0

  B. 13.5

  C. 1.2

  D. 4.5

  E. 9.3

  Correct Answer: E

  The titration of a strong base with a weak acid produces a basic equivalence point. However, a basic equivalent point is not anything beyond 11 usually.

• Question 38:

  Given the following reaction, how might one shift the equilibrium to the left? N2(g) + 3H2(g) <...> 2NH3(g)

  A. Add N2(g)

  B. Add helium

  C. Decrease the pressure

  D. Remove NH3(g)

  E. Decrease the volume

  Correct Answer: C

  Decreasing the pressure shifts the equilibrium towards the side with more moles of gas. The left side has 4 moles of gas whereas the products has 2 moles of gas, thus the equilibrium will shift to the left. Adding an inert gas will not affect the equilibrium. The other options will shift the equilibrium to the right.

• Question 39:

  Rank the freezing point in ascending order of the following solutions:

  I. 2.0 m CH3OH

  II. 2.0 m NaCl

  III.

  2.0 m AlCl3

  A.

  III < II < I

  B.

  I > II > III

  C.

  I > III > II

  D.

  II > I > III

  E.

  I = II = III

  Correct Answer: A

  The solution that exhibits the highest freezing point is the one that has depressed the least. I – CH3OH does not disassociate and thus its van't hoff factor (i) is 1. (2 m × 1) = 2 II – NaCl dissociates into 2 ions, Na+ and Cl− (i = 2). (2 m × 2) = 4 III – AlCl3 dissociates into 4 ions, 1 Al, and 3 Cl− (i = 4). (2 m × 4) = 8

  CH3OH thus exhibits the smallest depression in freezing point, and thus has the higher boiling points. NaCl is 2nd, and AlCl3 is last, with the highest depression in freezing point.

• Question 40:

  Which of the following phase changes leads to a positive change in entropy value?

  A. Fusion

  B. Melting

  C. Sublimation

  D. Vaporization

  E. All of the above

  Correct Answer: E

  All of the answer choices lead to a positive change of entropy value. Also note, Fusion and Melting are the same thing.