Test Prep Test Prep Certifications OAT Questions & Answers

• Question 51:

  What is the oxidation state of nitrogen in the following compound: NaN3?

  A. +1/3

  B. +3

  C. +5

  D. -1/3

  E. -5

  Correct Answer: D

  The entire compound has a charge of 0. Thus, giving Na's +1 oxidation state: 1 + 3x = 0

  The 3x represents the nitrogen (3 of them, x being the unknown oxidation number), the 1 represents the +1 oxidation number of Na and finally the 0 being the neutral charge of the entire compound. Solving for x:

  3x = -1 x = -1/3

• Question 52:

  Given this hypothetical compound, K2X2F2. Find the atomic weight of the unknown element, X, if the molar mass of the compound itself totals 162 g/mol.

  A. 23 g/mol

  B. 30 g/mol

  C. 35 g/mol

  D. 46 g/mol

  E. 50 g/mol

  Correct Answer: A

  Looking at the periodic table, add up the molar mass of the elements that are known. 2K gives (39 + 39), and 2F gives (19 + 19):

  39 + 39 + 19 + 19 = 116

  Thus, 116 is 46 short of the total 162, thus there has to be 46 g of the unknown `X'. Since there are 2 moles of this, the atomic weight of this element has to be 23 g/mol.

• Question 53:

  What is the total number of orbitals in the third shell (n = 3)?

  A. 1

  B. 4

  C. 9

  D. 16

  E. 25

  Correct Answer: C

  The number of orbitals per level can be expressed with the equation: n2

  Where n = 3.

  32 = 9

  9 total orbitals exist. (1 from s-orbital, 3 from p-orbitals, 5 from d-orbitals).

• Question 54:

  Which of the following molecules is incorrectly matched to its molecular geometry?

  A. BeCl2 – Linear

  B. BF3 – Trigonal planar

  C. SO2 – Bent

  D. SF6 – Square pyramidal

  E. NH3 – Trigonal pyramidal

  Correct Answer: D

  SF6 is octahedral. It is vital to know the basic VSEPR system, ranging from bond angles to molecular geometry.

• Question 55:

  In the following equilibrium, which of the following actions will shift the equilibrium to the right?

  3H2(g) + N2(g) <...> 2NH3(g)

  A. Adding extra NH3(g)

  B. Removing N2(g)

  C. Removing H2(g)

  D. Increasing the pressure

  E. None of the above

  Correct Answer: D

  Answer choices [Adding extra NH3(g)], [Removing N2(g)], [Removing H2(g)] all cause the reaction to shift to the left (towards the reactants). Increasing the pressure shifts the reaction towards the side with the fewer molecules (in this case, the product side). Thus, increasing the pressure shifts the reaction to the right to restore equilibrium.

• Question 56:

  Calculate the pOH of 3 × 10−4M HCI

  A. 3.00

  B. 3.52

  C. 5.21

  D. 10.48

  E. 11.13

  Correct Answer: D

• Question 57:

  A mythical atom has isotopes: 10X, 11X and 12X with masses 10, 11, and 12 respectively. 10X has an abundance of 80%, 11X of 15% and 12X of 5%. What is the atomic mass of this X atom?

  A. 10

  B. 10.25

  C. 10.75

  D. 11

  E. 11.25

  Correct Answer: B

  Logically you should be aware the answer is going to be a low 10 number due to the vast abundance of the 10 atom. However, to calculate it mathematically: (0.80 × 10) + (0.15 × 11) + (0.05 × 12) = 10.25

• Question 58:

  If 500 mL of 0.5M HBr is diluted to 0.4M HBr, what is the final volume?

  A. (500) (0.4 / 0.5)

  B. (500) (0.5 / 0.4)

  C. (0.5 / 500) (0.4)

  D. (500) (0.20)

  E. (500 - 0.4) (0.5)

  Correct Answer: B

  This is a simple case of (initial molarity) (initial volume) = (final molarity) (final volume).

• Question 59:

  What is the total number of atoms contained in 2 moles of sulfur?

  A. 6.02 × 1023

  B. 32

  C. 64

  D. 1.2 × 1024

  E. 6.02 × 1024

  Correct Answer: D

  One mole of anything is 6.02 × 1023 atoms. So, two moles are simply twice that. This is a very easy conceptual question that can confuse test takers as they overthink it. Do not double the atomic mass.

• Question 60:

  Which of the following processes is an example of deposition?

  A. H2O(s) –andgt; H2O(l)

  B. H2O(l) –andgt; H2O(g)

  C. H2O(s) –andgt; H2O(g)

  D. H2O(g) –andgt; H2O(l)

  E. H2O(g) –andgt; H2O(s)

  Correct Answer: E