Admission Tests Admission Tests Certifications PCAT Questions & Answers

• Question 191:

  Which of the following would show the greatest number of peaks at different values on a proton NMR?

  A. CH4

  B. CH3CH3

  C. CH3CH2CH2CH3

  D. CH3CH2CH2OH

  Correct Answer: D

• Question 192:

  If a substance has a constant half-life of 10 weeks, how many grams of a 12 g sample would remain after 30 weeks?

  A. 8 g

  B. 6 g

  C. 3 g

  D. less than 2 g

  Correct Answer: D

  Thirty weeks corresponds to 3 half-lives. After the first half life (10 weeks), there will be 12 ?2 = 6 g remaining. After another 10 weeks, there will be 3 g remaining. And after the final 10 weeks, there will be

  1.5 g remaining.

• Question 193:

  An element whose atomic number is 16 would have how many unpaired electrons?

  A. 0

  B. 1

  C. 2

  D. 4

  Correct Answer: C

  The atomic number indicates the number of protons (and electrons). Writing the electron configuration: 1s2 2s2 2p6 3s2 3p4 (2 + 2 + 6 + 2 + 4 = 16). The 3p orbital will contain 1 filled orbital, and 2 half-filled orbitals, which indicates 2 unpaired electrons.

• Question 194:

  Which effect does remove a solute have?

  A. increases the boiling point

  B. increases the melting point

  C. increases the freezing point

  D. decreases the vapor pressure

  Correct Answer: C

  The addition of a solute to a solvent lowers the freezing point of the solution due to the pressure added to the solvent. Consequently, the removal of a solute from a solvent must have the opposite effect and increase the freezing point.

• Question 195:

  What is the partial pressure of nitrogen in a gas of 30 atm made of equal moles of oxygen, nitrogen and carbon?

  A. 3 atm

  B. 10 atm

  C. 15 atm

  D. 30 atm

  Correct Answer: B

  Dalton's law states that the total pressure of a gas mixture is equal to the sum of the partial pressures. In this case, the total pressure is 30 atm, which is the result of 3 equally combined gases. Dividing the total pressure by the number of gases yields the partial pressure of each gas: 30 ?10 = 10 atm.

• Question 196:

  Which of the following are reducing agents?

  A. FADH2

  B. NAD+

  C. NADH

  D. Both A and C

  Correct Answer: D

  Reducing agents are those that donate electrons in redox chemical reactions. Cellular respiration involves the carrying of electrons by both FADH2 and NADH, because both must be included in the answer.

• Question 197:

  What is the conjugate acid of HCl?

  A. Cl-

  B. Cl2

  C. H2Cl+

  D. H2O

  Correct Answer: C

  The conjugate acid of a compound results from the addition of a proton (H+). The theoretical conjugate acid of HCl would be: HCl + H+ ?gt; H2Cl+.

• Question 198:

  What is the hybridization of the carbons in benzene?

  A. s

  B. sp

  C. sp2

  D. sp3

  Correct Answer: C

  Benzene, C6H6, is a planar regular hexagon made up of a ring of carbon atoms. Each carbon is bonded with 2 other carbon atoms as well as a hydrogen atom for a total of 3 bonded atoms. Consequently, the hybridization of benzene is sp2.

• Question 199:

  If the pI of a specific protein is 6, what is the charge on the protein when it is in a solution of pH 9?

  A.

  B. 0

  C. +

  D. Cannot be determined.

  Correct Answer: A

  The pI, or the isoelectric point, is the pH at which a molecule exhibits a net charge of 0. When the pI of a molecule is less than the pH of the surrounding solution, the molecule is deprotonated and its charge is negative. The 3 situations:

  pH < pI = protonated (+ charge) pH > pI = deprotonated (- charge) pH = pI = neutral charge.

• Question 200:

  Which of the following alcohols is the most easily dehydrated?

  A. (CH3)3C-OH

  B. (CH3)2CH-OH

  C. CH3CH2-OH

  D. CH3-OH

  Correct Answer: A

  Classify the alcohols as primary, secondary, or tertiary: (CH3)3C-OH is tertiary because the -OH group is directly attached to 3 alkyl groups; (CH3)2CH-OH is secondary because the carbon attached to the -OH is connected to 2 carbon atoms; CH3CH2-OH is primary because the carbon connected to the -OH group is connected to 1 carbon atom; and although CH3-OH lacks an attached alkyl group, it is considered primary. As tertiary alcohols form the most stable carbocations.