Admission Tests Admission Tests Certifications PCAT Questions & Answers

• Question 171:

  How many sigma bonds does HCCH have?

  A. 1

  B. 2

  C. 3

  D. 4

  Correct Answer: C

  Recall that single bonds are always sigma bonds, double bonds consist of a sigma bond and a pi bond, and triple bonds contain one sigma bond and two pi bonds. HCCH contains 2 C璈 bonds and 1 C瑿 triple bond. So, 2 C-H bonds gives 2 sigma bonds, and another sigma bond from the triple bond equals 3 sigma bonds.

• Question 172:

  Which law states that the volume of a gas is proportional to the number of moles of a gas at constant temperature and pressure?

  A. Dalton's law

  B. Avogadro's law

  C. Charles's law

  D. Henry's law

  Correct Answer: B

  Avogadro's law relates the volume of a gas to the amount of substance of gas present: V = nk, where V is the volume of the gas, n is the number of moles of the gas, and k is the a constant equal to RT / P where R is the universal gas constant, T is temperature in Kelvins, and P is the pressure.

• Question 173:

  Which of the compounds has the lowest boiling point?

  A. CH3(CH2)2CH3

  B. CH3CH(CH3)2

  C. CH3(CH2)2CH2OH

  D. CH3CH(CH3)OH

  Correct Answer: B

  When comparing boiling points among compounds, consider these 3 generalities:

  (1)

  boiling point increases relative to the strength of the intermolecular forces present in the compound; ionic bonding is stronger than hydrogen bonding is stronger than dipole bonding is stronger than Van der Waals forces.

  (2)

  Boiling point also increases as the molecular weight of the compound increases.

  (3)

  Branching of the compound decreases the boiling point (mitigation of Van der Waals forces).

• Question 174:

  What is the osmotic pressure of a 2M NaCl solution at 0 degrees C?

  A. 44.8 atm

  B. 45.5 atm

  C. 0 atm

  D. 97 atm

  Correct Answer: A

  Calculate osmotic pressure using: π = MRT, where π is pressure, M is the molar concentration of the dissolved solution, R is the ideal gas constant (0.08206 L atm mol−1 K−1), and T is temperature in Kelvins. Substituting and solving: π = 2 × 0.08206 × 273.15 = 44.8 atm.

• Question 175:

  Which compound forms when acetyl-CoA enters the TCA cycle?

  A. oxaloacetate

  B. acetic acid

  C. citrate

  D. FADH2

  Correct Answer: C

  Prior to the TCA cycle, glycolysis functions to breakdown glucose into pyruvate which is then decarboxylated and turned into acetyl-CoA. Acetyl-CoA combines with oxaloacetate to make citrate, which marks the start of the TCA cycle.

• Question 176:

  FADH2 is classified as which of the following?

  A. oxidizing agent

  B. reducing agent

  C. intermediate

  D. none of the above

  Correct Answer: B

  In cellular respiration, FADH2 acts as an electron carrier and donor. Reducing agents are those that lose electrons during a reaction. Oxidizing agents are those that gain electrons during a reaction. Oxidation of FADH2 results in FAD+, and FADH2 is a reducing agent.

• Question 177:

  Which of the following has the largest bond order?

  

  A. Option A

  B. Option B

  C. Option C

  D. Option D

  Correct Answer: D

  Bond order for diatomic molecules is found by determining the type of bonds between the 2 atoms. In cases where there are more than two atoms involved, count the number of bonds, then count the number of bond groups between atoms, then calculate the ratio of the number of bonds to the total number of bond groups. The Lewis structure for (A) shows a double bond between oxygen atoms, and its bond order is 2.

  (B)

  Shows a double bond between N and O, and 2 single bonds between N and O:

  (C)

  Shows 2 double bonds between N and O: 4 ?2 = 2. (D) Shows 1 triple bond between C and N and a bond order of 3. (D) has the largest bond order.

  

• Question 178:

  Which of the following would show a peak at 2190 cm-1?

  A. alkane

  B. alkene

  C. alkyne

  D. ketone

  Correct Answer: C

• Question 179:

  The ____ is the ____ at which a protein has no net charge.

  A. pH, pKa

  B. pI, pKa

  C. pH, pI

  D. pI, pH

  Correct Answer: D

  A protein will have no net charge when its composite amino acids taken together yield no overall charge. The pI, or isoelectric point, is the pH at which a molecule, in this case protein, carries no net charge.

• Question 180:

  The hybridization of the oxygen in CO2 is:

  A. s

  B. sp

  C. sp2

  D. sp3

  Correct Answer: C