PCAT Chemical Processes Practice Test

Below you will find our free PCAT Chemical Processes practice test. The PCAT exam includes 48 Chemistry questions that must be completed within 35 minutes. The topics covered are general chemistry, organic chemistry, and basic biochemistry processes. Our practice questions are designed to be very challenging. Instant scoring is provided along with detailed explanations. Continue your test prep now with our PCAT practice questions.

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Question 1
Which molecule is nonpolar?

A
carbon monoxide
B
acetone
C
carbon tetrachloride
D
ethanol
Question 1 Explanation: 
The correct answer is (C). Carbon tetrachloride is the only nonpolar compound because it is the only compound listed in which all of the electrons are shared equally across the four same bonds; each chlorine atom bonds with the carbon atom with the same force. Consequently, carbon tetrachloride exhibits a tetrahedral structure with geometric symmetry.
Question 2
A 50mL solution of HCl is diluted to 250mL at 10M. What was the initial concentration of the HCl?

A
500M
B
50M
C
5M
D
0.5M
Question 2 Explanation: 
The correct answer is (B). The product of the initial concentration and the initial volume is equal to the product of the final concentration and the final volume of the solution. This can be remembered as:
c1 * v1 = c2 * v2
Substitute the known quantities and solve for the unknown:
c1: c1 * 50mL = 10M * 250mLc1 = 50M
Question 3
What product results from treating ethanol with pyridinium chlorochromate (PCC)?

A
acetaldehyde
B
formaldehyde
C
acetone
D
acetic acid
Question 3 Explanation: 
The correct answer is (A). PCC is a mild oxidizing reagent used to oxidize primary alcohols to aldehydes. Ethanol, a primary alcohol, treated with PCC results in a 2 carbon aldehyde (because of the 2 carbons initially present in ethanol) called ethanal, or acetaldehyde.
Question 4
What are the relative pKa values of the following compounds?

I.    H2O

II.   NH3

III.  HCl

IV. CH3COOH

A
II > I > IV > III
B
IV > II > III > I
C
III > IV > I > II
D
I > III > IV > II
Question 4 Explanation: 
The correct answer is (A). Categorize the options as strong acids, weak acids, neutral, weak bases, or strong bases and rank. (I) is neutral; (II) is basic; (III) is strongly acidic; (IV) is weakly acidic. Low pKa values correspond to higher acidity levels, so (III) will have the lowest pKa and (II) will have the highest pKa value.
Question 5
What is the oxidation number of nitrogen in NF3 ?

A
−3
B
0
C
+2
D
+3
Question 5 Explanation: 
The correct answer is (D). The sum of the oxidation numbers of a neutral compound is always 0. The oxidation number of fluorine is always −1. Let x represent the oxidation number of N, set up the equation, and solve for x:
x + (−1) * 3 = 0 → x = 3
Question 6
What is the conjugate base of sulfuric acid?

A
c1a
B
c2b
C
c3c
D
c4d
Question 6 Explanation: 
The correct answer is (B). In a solution, sulfuric acid will donate an H+ to water to form hydronium (H3O+). The loss of the single H+ results in H2SO4 becoming HSO4¯.
Question 7
What would be the result of increasing the number of nucleophiles in a SN1 reaction?

A
It would increase the rate exponentially
B
It would increase the rate linearly
C
It would decrease the rate
D
It would have no effect
Question 7 Explanation: 
The correct answer is (D). SN1 reactions are substitution reactions that depend on reagents attracted to electrons (electrophiles). SN1 reactions do not depend on the number of nucleophiles involved in the reaction. Consequently, altering the concentration of nucleophiles does not alter the rate of reaction.
Question 8
Which of the following species cannot hydrogen bond with itself?

A
ethanol
B
acetic acid
C
ammonia
D
acetone
Question 8 Explanation: 
The correct answer is (D). Hydrogen bonds occur between hydrogen of one molecule with an electronegative atom (oxygen, nitrogen, or fluorine) of another atom. Consequently, acetone is unable to hydrogen bond with itself. The hydrogen atoms in acetone are covalently bonded to carbon atoms and not a strong electronegative atom like nitrogen, oxygen, of fluorine.
Question 9
Which effect would result from increasing the molar mass of a gas?

A
An increase in temperature
B
An increase on pressure
C
An increase in volume
D
A decrease in the rate
Question 9 Explanation: 
The correct answer is (D). Graham’s Law of Diffusion states that the rate of diffusion is inversely proportional to the molecular weight of the molecule. Let the initial molar mass be 5, and the increased molar mass be 10, substitute these values into Graham’s equation and compare the results:
c5
The rate has decreased with the increase in molar mass.
Question 10
Rank the following amino acids by increasing pI (isoelectric point):

I.   Lys

II.  Leu

III. Asp

A
I < II < III
B
III < II < I
C
II < I < III
D
III < I < II
Question 10 Explanation: 
The correct answer is (B). The pI of a molecule is its isoelectric point, or the point at which, in this case, the amino acid will have no overall charge. Categorizing the amino acids: (I) is positively charged and basic; (II) is non polar and neutral; (III) is polar and acidic. Acidic amino acids on average have the lowest pI, nonpolar amino acids have a higher pI, and basic amino acids carry the largest pI.
Question 11
What is the result of adding HBr and hydrogen peroxide to propene?

A
2-propanol
B
1-propanol
C
2-bromopropane
D
1-bromopropane
Question 11 Explanation: 
The correct answer is (D). In the presence of an organic peroxide, the addition of HBr (and peroxide) to a propene results in an anti-Markovnikov product in which the hydrogen becomes attached to the carbon with fewer hydrogens connected to it. The product of the addition is CH3CH2CH2Br, or 1-bromopropane.
Question 12
Which of the following has the highest boiling point?

A
methanol
B
n-propanol
C
isopropanol
D
ethanol
Question 12 Explanation: 
The correct answer is (B). Boiling points primarily depend upon the cohesive forces between molecules. When dealing with molecules of relatively similar molecular weights, the boiling points will depend upon the functional groups involved, and as the molecular weight of the molecule increases, the boiling point also increases. Lastly, branching decreases boiling point. With these considerations, n-propanol will exhibit the highest boiling point of the options.
Question 13
The rate law for a reaction is of the second order. Which statement is true?

A
The rate must depend on both reactants.
B
The reaction must depend on the square of one reactant.
C
The reaction must depend on only k squared.
D
The reaction must depend on at least one of the reactants.
Question 13 Explanation: 
The correct answer is (D). In a second-order reaction the reaction rate is dependent upon either the product of the reactants, or the square of one of the reactants. Only answer choice (D) fits this definition.
Question 14
The solubility of KCl in seawater would be ____ than the solubility of KCl in tap water.

A
higher
B
the same as
C
lower
D
KCl would completely insoluble in sea water as K cannot dissociate in water.
Question 14 Explanation: 
The correct answer is (C). Potassium chloride is a metal halide salt. And, while it dissolves readily in water, its solubility is lowered because of the common ions present in the seawater. This is otherwise known as the common ion effect.
Question 15
An electron pair donor is best classified as a

A
strong acid
B
Bronsted-Lowry acid
C
Lewis acid
D
Lewis base
Question 15 Explanation: 
The correct answer is (D). By definition, a Lewis base is an electron pair donor. A Lewis acid, on the other hand, is an electron pair acceptor.
Question 16
Which reaction can be spontaneous under favorable conditions?

I.    −∆H, +∆S

II.   −∆H, −∆S

III.  +∆H, −∆S

A
I only
B
II only
C
I and III only
D
I and II only
Question 16 Explanation: 
The correct answer is (D). Under favorable conditions, ∆H < 0, and ∆S > 0, a reaction will be spontaneous at any temperature. If one of the conditions is unfavorable with either ∆H > 0 or ∆S < 0, a reaction can be spontaneous if it satisfies ∆G < 0 using the standard-state free energy of reaction equation: ∆G = ∆H − T∆S. Roman numeral (I) satisfies both favorable conditions and will be spontaneous. Roman numeral (II) can be spontaneous if ∆H is sufficiently low. Roman numeral (III) can never be spontaneous.
Question 17
Which of the following alcohols is the most easily dehydrated?

A
(CH3)3C−OH
B
(CH3)2CH−OH
C
CH3CH2−OH
D
CH3−OH
Question 17 Explanation: 
The correct answer is (A). Classify the alcohols as primary, secondary, or tertiary: (A) is tertiary because the −OH group is directly attached to 3 alkyl groups; (B) is secondary because the carbon attached to the −OH is connected to 2 carbon atoms; (C) is primary because the carbon connected to the −OH group is connected to 1 carbon atom; and although (D) lacks an attached alkyl group, it is considered primary. As tertiary alcohols form the most stable carbocations, (A) is correct.
Question 18
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
Question 18 Explanation: 
The correct answer is (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 19
What is the hybridization of the carbons in benzene?

A
s
B
sp
C
sp2
D
sp3
Question 19 Explanation: 
The correct answer is (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 20
What is the conjugate acid of HCl?

A
Cl‾
B
Cl2
C
H2Cl+
D
H2O
Question 20 Explanation: 
The correct answer is (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+ → H2Cl+.
Question 21
Which of the following are reducing agents?

A
FADH2
B
NAD+
C
NADH
D
Both A and C
Question 21 Explanation: 
The correct answer is (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, (D) is correct.
Question 22
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
Question 22 Explanation: 
The correct answer is (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 23
Which effect does removing a solute have?

A
increases the boiling point
B
increases the melting point
C
increases the freezing point
D
decreases the vapor pressure
Question 23 Explanation: 
The correct answer is (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 24
An element whose atomic number is 16 would have how many unpaired electrons?

A
0
B
1
C
2
D
4
Question 24 Explanation: 
The correct answer is (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 25
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
Question 25 Explanation: 
The correct answer is (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 26
Rank the following compounds based on increasing acidity:

I.    CH3CH2OH

II.   CH3COCH3

III.  CH3CH2COH

IV.  CH3CH2COOH

A
II, III, IV, I
B
II, IV, I, III
C
II, III, I, IV
D
IV, I, III, II
Question 26 Explanation: 
The correct answer is (C). There are no strong acids present in the answer choices. There is only one weak acid present in the answer choices, CH3CH2COOH. The presence of the carboxyl group indicates a weak acid. Because there are no other weak acids, (IV) must be the most acidic compound included, so answer choice (C) is correct.
Question 27
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
Question 27 Explanation: 
The correct answer is (D). The peaks in a proton NMR correspond to the number of different environments containing hydrogen. All protons in methyl (CH3) and methylene (CH2) groups are equivalent because they exist in the same environment. So, methyl and methylene both contain 2 peaks. 1-Propanol, however, includes 3 environments (CH2,CH3,OH) and would contain the greatest number of peaks.
Question 28
The distribution of electrons evenly in a molecule contributes to stability. This accounts for:

A
atomic mass
B
valence
C
resonance
D
electronegativity
Question 28 Explanation: 
The correct answer is (C). Resonance describes the possible positions of electrons within a molecule when more than one possibility exists. Molecules that have multiple resonance structures display greater stability than those with fewer resonance structures.
Question 29
Which of the following would have the highest pH in a solution?

A
hydrofluoric acid
B
water
C
ammonia
D
hydrochloric acid
Question 29 Explanation: 
The correct answer is (C). Because ammonia can accept protons from water molecules, it is considered basic. Water is considered neutral, and both hydrofluoric and hydrochloric acid have low pH’s because they ionize in aqueous solutions. Ammonia, a base, has the highest pH of the answer choices.
Question 30
The addition of HBr with peroxide and an alkene yields what product?

A
Markovnikov’s product
B
anti-Markovnikov’s product
C
Sayteffs product
D
the ortho product
Question 30 Explanation: 
The correct answer is (B). In the absence of peroxide, HBr plus an alkene yields Markovnikov’s product. But, in the presence of peroxide, the result of the reaction is an anti-Markovnikov’s product.
Question 31
In which locations does this reaction occur?

Glyceraldehyde-3-phosphate (G3P) --------→ Pyruvate

A
cytoplasm
B
nucleus
C
mitochondria
D
none of the above
Question 31 Explanation: 
The correct answer is (A). The oxidation of G3P into pyruvate occurs during the glycolysis stage of cellular respiration. Glycolysis occurs in the cytoplasm.
Question 32
Which would yield an endothermic reaction?

A
∆G = 298
T = 298
∆S = −1
B
∆G = −298
T = 298
∆S= −2
C
∆G = −298
T = 0
∆S = 1
D
none of them
Question 32 Explanation: 
The correct answer is (D). The free energy change of a reaction, ∆G, is equal to the difference between ∆H, the change in enthalpy, and the product of the temperature, T, with the change in entropy, ∆S, of the system: ∆G = ∆H − T∆S. An endothermic reaction requires a ∆H > 0. Solve for ∆H in each case. (A): 0, (B): −894, (C): −298.
Question 33
______ law states that the ______ is the sum of ______ in a gas compound.

A
Dalton’s, partial pressure, total pressure
B
Henry’s, partial pressure, total pressure
C
Dalton’s, total pressure, partial pressures
D
Henry’s, total pressure, partial pressures
Question 33 Explanation: 
The correct answer is (C). Dalton’s law states that the total pressure of a gaseous compound is the sum of the partial pressures of each gas making up the compound:
c6
Question 34
What effect would doubling the volume and temperature of an ideal gas have on its pressure?

A
double the pressure
B
half the pressure
C
make the pressure zero
D
no effect
Question 34 Explanation: 
The correct answer is (D). The ideal gas law states: pV = NRT, where p is pressure, V is volume, N is the amount, R is the ideal gas constant, and T is the gas’s temperature. Doubling the volume, V = 2V, and doubling the temperature, T = 2T, will have not alter the pressure because the 2’s on both sides of the equation will cancel, yielding the original pressure.
Question 35
What is the molecular formula of acetic acid?

A
C2H4O2
B
C3H6O
C
CH2O
D
CHO
Question 35 Explanation: 
The correct answer is (A). Acetic acid is often produced by way of methanol carbonylation wherein methanol, CH3OH, reacts with carbon monoxide, CO, to produce acetic acid, CH3COOH. Rewriting in terms of the molecular formula, CH3COOH = C2H4O2.
Question 36
The hybridization of the oxygen in CO2 is:

A
s
B
sp
C
sp2
D
sp3
Question 36 Explanation: 
The correct answer is (C). An analysis of the Lewis structure for CO2 shows a steric number of 2 for the carbon atom because of the 2 oxygen atoms attached (no lone pairs). Each oxygen atom has 2 lone pairs and is connected with the carbon atom, so a steric number of 3, and consequently, a hybridization of sp2.
Question 37
An enzyme reaction reaches _____ at _____.

A
Vmax, Km
B
Vmax, ½Km
C
½Vmax, Km
D
½Vmax, ½Km
Question 37 Explanation: 
The correct answer is (C). Vmax is the maximum rate at which an enzymatic reaction can occur. Km is the substrate concentration yielding a reaction rate that is half of the maximum reaction rate.
Question 38
Which of the following would show a peak at 2190 cm−1?

A
alkane
B
alkene
C
alkyne
D
ketone
Question 38 Explanation: 
The correct answer is (C). Alkynes, which possess a carbon to carbon triple bond, correspond with frequencies that range from 2300 cm−1 to 2100 cm−1. Alkanes, alkenes, and ketones involve C-H, C=C, and C=O bonds, respectively. None of the other bonds correspond to frequencies near 2190 cm−1.
Question 39
The ____ is the ____ at which a protein has no net charge.

A
pH, pKa
B
pI, pKa
C
pH, pI
D
pI, pH
Question 39 Explanation: 
The correct answer is (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 40
FADH2 is classified as which of the following?

A
oxidizing agent
B
reducing agent
C
intermediate
D
none of the above
Question 40 Explanation: 
The correct answer is (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 41
Which of the following has the largest bond order?

A
c8a
B
c8b
C
c8c
D
c8d
Question 41 Explanation: 
The correct answer is (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:
c7
(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 42
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
Question 42 Explanation: 
The correct answer is (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 43
Which compound forms when acetyl-CoA enters the TCA cycle?

A
oxaloacetate
B
acetic acid
C
citrate
D
FADH2

Question 43 Explanation: 
The correct answer is (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 44
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
Question 44 Explanation: 
The correct answer is (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 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). Under these considerations, answer choice (B) is correct.
Question 45
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
Question 45 Explanation: 
The correct answer is (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 46
How many sigma bonds does HCCH have?

A
1
B
2
C
3
D
4
Question 46 Explanation: 
The correct answer is (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-H bonds and 1 C-C triple bond. So, 2 C-H bonds gives 2 sigma bonds, and another sigma bond from the triple bond equals 3 sigma bonds.
Question 47
Which of the following reactions creates an alkene?

A
addition
B
substitution
C
hydration
D
dehydration
Question 47 Explanation: 
The correct answer is (D). Dehydration involves the loss of an H2O molecule from the reacting molecule. Recall that the general structure of alcohols is: CNH2n + 1OH. The removal of H2O from an alkyl group results in a molecule of the general form: CNH2nOH, also known as an alkene. Consequently, (D) is the correct answer.
Question 48
The viscosity of a liquid

A
increases with decreasing temperature
B
increases with increasing temperature
C
decreases with decreasing temperature
D
is independent of temperature
Question 48 Explanation: 
The correct answer is (A). A liquid’s viscosity, or its resistance to flow, changes with a change in temperature. As a liquid’s temperature increases, bonds within it break and the molecules in the liquid can move more freely and easily, decreasing its viscosity. Likewise, if the temperature decreases, molecules have more of an opportunity to form bonds which then decreases the liquid’s fluidity, increasing its viscosity.
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