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AP Chemistry Full-length practice exam 1

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Full-length practice exam 1

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Question 1

How many grams of $H_{2} O$ are produced when $4.00 g$ of $H_{2}$ reacts completely with excess $O_{2}$ ?

$2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (g)$

(Molar masses: H $_{2}$ = 2.02 g/mol, H $_{2}$ O = 18.02 g/mol)

36.0 g

18.0 g

9.00 g

72.1 g

Question 2

For the reaction $PC l_{5} (g) ⇌ PC l_{3} (g) + C l_{2} (g)$ , $K_{c} = 1.8 \times 1 0^{- 2}$ at a certain temperature. If a reaction mixture has $[PC l_{5}] = 0.50 M$ , $[PC l_{3}] = 0.15 M$ , and $[C l_{2}] = 0.15 M$ , in which direction will the reaction proceed?

A.Forward, toward products, because

Q < K_{c}

.B.Reverse, toward reactants, because

Q > K_{c}

.C.Neither; the system is at equilibrium because all concentrations are nonzero.D.Forward, because the products have lower concentrations than the reactant.

Question 3

At $25° C$ , the enthalpy of combustion of hydrogen is $- 241.8 kJ/mol$ (as gas) when $H_{2} O$ is formed as a vapor. The enthalpy of vaporization of water is $44.0 kJ/mol$ . What is the enthalpy of combustion when liquid water is formed?

- 197.8 kJ/mol

- 285.8 kJ/mol

- 241.8 kJ/mol

+ 44.0 kJ/mol

Question 4

The $K_{w}$ for water at $25° C$ is $1.0 \times 1 0^{- 14}$ . If the pOH of a solution is $3.00$ , what is the pH?

3.00

7.00

11.00

14.0

Question 5

What is the electron-pair geometry and molecular geometry of $S F_{4}$ ?

A.Tetrahedral; tetrahedralB.Trigonal bipyramidal; trigonal bipyramidalC.Trigonal bipyramidal; see-sawD.Octahedral; square planar

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Question 6

Adding an inert gas to a gaseous equilibrium system at constant volume has what effect on the equilibrium position?

A.Shifts toward the side with more moles of gas.B.Shifts toward the side with fewer moles of gas.C.No shift; the equilibrium position is unchanged.D.Shifts forward to consume the extra pressure.

Question 7

In an electrolytic cell, which statement correctly describes the process?

A.A spontaneous reaction drives electron flow through the external circuit.B.External electrical energy forces a non-spontaneous redox reaction.C.The anode is negative; the cathode is positive.D.Both oxidation and reduction occur at the same electrode.

Question 8

A $100.0 mL$ sample of $0.100 M$ acetic acid ( $p K_{a} = 4.74$ ) is titrated with $0.100 M$ NaOH. After adding $50.0 mL$ of NaOH, what is the pH?

7.00

4.74

2.87

8.72

Question 9

In a balanced redox equation in acidic solution, $Mn O_{4}^{-}$ is reduced to $M n^{2 +}$ while $F e^{2 +}$ is oxidized to $F e^{3 +}$ . How many $F e^{2 +}$ ions are required to reduce one $Mn O_{4}^{-}$ ?

2

3

5

7

Question 10

At equilibrium, increasing the pressure on a gas-phase reaction by reducing volume will shift the equilibrium in the direction that:

A.Decreases the total number of moles of gas.B.Increases the total number of moles of gas.C.Has no effect, since gases are compressible.D.Increases temperature.

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Question 11

For the reaction $2 N O_{2} (g) \to 2 NO (g) + O_{2} (g)$ , experimental data shows that doubling $[N O_{2}]$ increases the initial rate by a factor of 4. What is the rate law and overall reaction order?

rate = k [N O_{2}]

; first order overallB.

rate = k [N O_{2}]^{2}

; second order overallC.

rate = k [N O_{2}]^{2} [NO] [O_{2}]

; fourth order overallD.

rate = k [N O_{2}]^{1/2}

; half order overall

Question 12

Which type of intermolecular force is present in ALL molecular substances?

A.Hydrogen bondingB.Dipole–dipole forcesC.London dispersion forcesD.Ion–dipole forces

Question 13

The Bohr model correctly predicts the emission spectrum of hydrogen. However, it fails for multi-electron atoms primarily because it:

A.Assumes circular orbits and ignores electron–electron repulsion.B.Does not quantize electron energy levels.C.Ignores the wave nature of light entirely.D.Places electrons in the nucleus.

Question 14

The theoretical yield of aspirin in a synthesis reaction is $2.70 g$ , but a student collects only $2.16 g$ . What is the percent yield?

80.0%

125%

20.0%

54.0%

Question 15

What is the pH of a $0.010 M$ solution of $HCl$ ?

1.0

2.0

3.0

12.0

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Question 16

Which of the following aqueous solutions is the strongest base?

0.10 M

N H_{3}

(

K_{b} = 1.8 \times 1 0^{- 5}

)B.

0.10 M

NaOH

0.10 M

C H_{3} N H_{2}

(

K_{b} = 4.4 \times 1 0^{- 4}

)D.

0.10 M

N a_{2} C O_{3}

Question 17

Which of the following processes has a positive entropy change ( $Δ S > 0$ )?

H_{2} O (l) \to H_{2} O (s)

(freezing)B.

N_{2} (g) + 3 H_{2} (g) \to 2 N H_{3} (g)

NaCl (s) \to N a^{+} (aq) + C l^{-} (aq)

C O_{2} (g) \to C O_{2} (s)

(dry ice)

Question 18

A proposed mechanism for a reaction is:

Step 1 (slow): $N O_{2} + N O_{2} \to N O_{3} + NO$

Step 2 (fast): $N O_{3} + CO \to N O_{2} + C O_{2}$

What is the overall reaction and the predicted rate law?

A.Overall:

N O_{2} + CO \to NO + C O_{2}

; rate

= k [N O_{2}] [CO]

B.Overall:

N O_{2} + CO \to NO + C O_{2}

; rate

= k [N O_{2}]^{2}

C.Overall:

2 N O_{2} + CO \to N O_{3} + NO + C O_{2}

; rate

= k [N O_{2}]^{2} [CO]

D.Overall:

N O_{2} + CO \to NO + C O_{2}

; rate

= k [N O_{3}] [CO]

Question 19

In a bomb calorimeter experiment, $1.00 g$ of glucose ( $M = 180 g/mol$ ) causes a temperature rise of $2.00° C$ in a calorimeter with heat capacity $C_{cal} = 7.78 kJ/°C$ . What is the molar heat of combustion of glucose?

- 15.6 kJ/g

- 2800 kJ/mol

- 5330 kJ/mol

- 156 kJ/mol

Question 20

How many lone pairs of electrons are on the central nitrogen atom in $N H_{3}$ ?

0

1

2

3

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Question 21

The average bond enthalpy of an O=O double bond is $498 kJ/mol$ and that of an O–H bond is $464 kJ/mol$ . Using bond enthalpies, estimate $Δ H$ for:

$2 H_{2} (g) + O_{2} (g) \to 2 H_{2} O (g)$

( $D (H - H) = 436 kJ/mol$ )

- 478 kJ

- 484 kJ

+ 484 kJ

- 928 kJ

Question 22

Which of the following correctly ranks the entropy of three states of water at the same temperature?

S (ice) > S (water) > S (steam)

S (steam) > S (water) > S (ice)

S (water) > S (steam) > S (ice)

D.All three have equal entropy at the same temperature.

Question 23

For the second-order integrated rate law $\frac{1}{[ A ] _{t}} = k t + \frac{1}{[ A ] _{0}}$ , if $[A]_{0} = 0.500 M$ and $k = 0.0400 M^{- 1} \cdot s^{- 1}$ , what is $[A]$ after $100 s$ ?

0.167 M

0.250 M

0.100 M

0.333 M

Question 24

Which of the following describes a precipitation reaction?

HCl (aq) + NaOH (aq) \to NaCl (aq) + H_{2} O (l)

CaC l_{2} (aq) + N a_{2} S O_{4} (aq) \to CaS O_{4} (s) + 2 NaCl (aq)

Zn (s) + CuS O_{4} (aq) \to ZnS O_{4} (aq) + Cu (s)

2 H_{2} O_{2} (l) \to 2 H_{2} O (l) + O_{2} (g)

Question 25

During the titration of a weak acid (HA) with a strong base (NaOH), the half-equivalence point is reached when half the acid has been neutralized. At the half-equivalence point:

pH = 7.0

for all weak acids.B.

pH = p K_{a}

of the weak acid.C.

[A^{-}] = 0

because no conjugate base has formed yet.D.

pH

is highest at this point during the titration.

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Question 26

Assign oxidation numbers and identify the element that is oxidized in the following reaction:

$Zn (s) + 2 HCl (aq) \to ZnC l_{2} (aq) + H_{2} (g)$

A.H is oxidized (changes from

+ 1

0

).B.Zn is oxidized (changes from

0

+ 2

).C.Cl is oxidized (stays at

- 1

).D.Zn is reduced (changes from

0

+ 2

Question 27

Which electron configuration correctly represents a ground-state sulfur ( $Z = 16$ ) atom?

[Ne] 3 s^{2} 3 p^{4}

[Ne] 3 s^{2} 3 p^{6}

[Ne] 3 s^{2} 3 p^{2}

[Ne] 3 s^{1} 3 p^{5}

Question 28

A student burns $1.00 g$ of ethanol in a calorimeter containing $500 g$ of water. The temperature rises from $22.5° C$ to $35.7° C$ . What is the heat absorbed by the water? ( $c_{water} = 4.18 J/ (g \cdot °C)$ )

2.76 kJ

27.6 kJ

55.2 kJ

0.276 kJ

Question 29

Which of the following best explains why ionic compounds have high melting points compared with molecular compounds?

A.Ionic compounds are denser, so more energy is needed to expand the lattice.B.Ionic bonds are covalent in nature and therefore very strong.C.Electrostatic forces between oppositely charged ions in the crystal lattice are very strong.D.Ionic compounds cannot conduct electricity, which raises their melting points.

Question 30

Which of the following molecules is polar?

B F_{3}

CC l_{4}

C O_{2}

H_{2} S

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Question 31

An Arrhenius plot of $ln k$ vs $1/ T$ gives a straight line with slope $- 8000 K$ . What is the activation energy $E_{a}$ ? ( $R = 8.314 J/ (mol \cdot K)$ )

9.63 kJ/mol

66.5 kJ/mol

8000 kJ/mol

960 kJ/mol

Question 32

What is the formal charge on the oxygen atom in $C O_{2}$ (a carbon–oxygen double bond)?

- 2

- 1

0

+ 1

Question 33

In which of the following does the reaction become spontaneous as temperature increases from low to high?

Δ H = - 80 kJ

Δ S = - 200 J/K

Δ H = + 60 kJ

Δ S = + 150 J/K

Δ H = - 60 kJ

Δ S = + 150 J/K

Δ H = + 80 kJ

Δ S = - 200 J/K

Question 34

When $HF$ ionizes in water, fluoride ion is formed. Why is $F^{-}$ a stronger base than $C l^{-}$ ?

A.Fluorine has a higher electronegativity, which makes the F–H bond stronger and F

^{-}

more reluctant to give it up.B.

F^{-}

is smaller and holds its charge density over a smaller volume, making it a better proton acceptor (stronger base).C.

F^{-}

has a higher negative charge than

C l^{-}

.D.F

^{-}

has more lone pairs available for proton donation.

Question 35

A student draws a Lewis structure for $N O_{2}^{-}$ (nitrite ion) in which nitrogen forms one single bond to one oxygen and one double bond to the other, with one lone pair on nitrogen. What is the formal charge on the nitrogen in this structure?

+ 1

0

- 1

- 2

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Question 36

The common-ion effect predicts that the molar solubility of AgCl ( $K_{s p} = 1.8 \times 1 0^{- 10}$ ) in a $0.10 M$ NaCl solution is:

A.Greater than

1.3 \times 1 0^{- 5} M

1.3 \times 1 0^{- 5} M

(unchanged)C.

1.8 \times 1 0^{- 9} M

1.8 \times 1 0^{- 10} M

Question 37

The rate of decomposition of $N_{2} O_{5}$ is measured at two temperatures:

Temperature	Rate constant $k$
$25° C$	$3.0 \times 1 0^{- 5} s^{- 1}$
$45° C$	$1.2 \times 1 0^{- 4} s^{- 1}$

Which statement about this data is correct?

A.The reaction rate doubles for every

10° C

increase because that is a chemistry rule.B.The rate constant increases by a factor of 4 over a 20°C range, consistent with Arrhenius behavior.C.The rate constant doubles when temperature is doubled, so the reaction is second order in temperature.D.The rate constant is independent of temperature for a first-order reaction.

Question 38

For a reaction with $Δ H = + 120 kJ/mol$ and $Δ S = + 400 J/ (mol \cdot K)$ , at what temperature does the reaction become spontaneous?

A.Always spontaneous, regardless of temperature.B.Above

300 K

C.Below

300 K

D.Never spontaneous, because

Δ H > 0

Question 39

Which of the following species has a trigonal planar molecular geometry?

N H_{3}

S O_{3}

PC l_{3}

Cl F_{3}

Question 40

What is the difference between heat ( $q$ ) and temperature ( $T$ )?

A.Heat and temperature are the same thing measured in different units.B.Temperature measures the average kinetic energy of particles; heat is the energy transferred due to a temperature difference.C.Heat is a property of objects; temperature is a form of energy.D.A large object always has more heat than a small object at the same temperature.

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Question 41

The standard Gibbs free energy is related to the equilibrium constant by $Δ G^{\circ} = - R T ln K$ . If $Δ G^{\circ} = 0$ , what is $K$ ?

K = 0

K = 1

K = \infty

K = e

Question 42

A sample of ideal gas has a volume of $10.0 L$ at $27° C$ . At constant pressure, to what temperature (in $° C$ ) must the gas be cooled to reduce its volume to $7.50 L$ ?

- 48° C

0° C

20.25° C

- 75° C

Question 43

A 5.00-L container holds $0.500 mol$ of an ideal gas at $27° C$ . What is the pressure in atm? ( $R = 0.0821 L \cdot atm/ (mol \cdot K)$ )

0.274 atm

2.46 atm

4.93 atm

0.492 atm

Question 44

What distinguishes a homogeneous catalyst from a heterogeneous catalyst?

A.A homogeneous catalyst is consumed in the reaction, while a heterogeneous catalyst is not.B.A homogeneous catalyst is in the same phase as the reactants; a heterogeneous catalyst is in a different phase.C.A homogeneous catalyst lowers activation energy; a heterogeneous catalyst does not.D.Homogeneous catalysts are always biological (enzymes); heterogeneous are always metals.

Question 45

Which of the following is the conjugate base of $H_{2} P O_{4}^{-}$ ?

H_{3} P O_{4}

HP O_{4}^{2 -}

P O_{4}^{3 -}

H_{2} O

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Question 46

A $25.0 mL$ sample of $0.100 M$ HCl is titrated with $0.100 M$ NaOH. What is the pH at the equivalence point?

1.0

7.0

13.0

4.74

Question 47

The relationship between $K_{c}$ and $K_{p}$ for a gas-phase equilibrium is $K_{p} = K_{c} (R T)^{Δ n}$ , where $Δ n$ is the change in moles of gas. For the reaction $2 S O_{3} (g) ⇌ 2 S O_{2} (g) + O_{2} (g)$ , $Δ n =$ ?

- 1

+ 1

+ 2

0

Question 48

In a galvanic (voltaic) cell, which statement correctly describes the anode and cathode?

A.Oxidation occurs at the cathode; reduction at the anode.B.Reduction occurs at the cathode; oxidation at the anode.C.Both electrodes undergo oxidation simultaneously.D.The cathode is the positive electrode in both galvanic and electrolytic cells.

Question 49

At constant temperature, the pressure of a fixed amount of gas is increased from $1.00 atm$ to $4.00 atm$ . By what factor does the volume change?

A.Increases by a factor of 4B.Decreases by a factor of 4C.Decreases by a factor of 2D.Remains unchanged

Question 50

The bond angle in $H_{2} O$ ( $\approx 104.5°$ ) is less than the ideal tetrahedral angle of $109.5°$ because:

A.Hydrogen atoms are very small and provide less steric repulsion.B.Lone pairs occupy more space than bonding pairs and compress the H–O–H angle.C.The O–H bonds are polar, causing electrostatic repulsion between the hydrogen atoms.D.Water uses

s p^{2}

hybridization, which gives 120° angles reduced by lone pairs.

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Question 51

For a reaction with $K_{c} = 5.0 \times 1 0^{- 8}$ , which statement best characterizes the equilibrium?

A.At equilibrium, the mixture contains mostly products.B.At equilibrium, reactants and products are present in roughly equal amounts.C.At equilibrium, the mixture is predominantly reactants.D.The reaction does not reach equilibrium because

K_{c}

is too small.

Question 52

According to the kinetic molecular theory of gases, what happens to the average kinetic energy of gas molecules when temperature is doubled (from 300 K to 600 K)?

A.It doubles.B.It quadruples.C.It increases by

2

.D.It remains the same; only pressure changes.

Question 53

Which hybridization is consistent with a carbon atom that forms two double bonds and no single bonds (as in $C O_{2}$ )?

s p^{3}

s p^{2}

s p

s p^{3} d

Question 54

The relationship between standard cell potential and Gibbs free energy is $Δ G^{\circ} = - n F E_{cell}^{\circ}$ , where $F = 96, 485 C/mol$ . For a cell with $E^{\circ} = + 0.50 V$ and $n = 2$ , what is $Δ G^{\circ}$ ?

+ 96.5 kJ/mol

- 96.5 kJ/mol

- 48.2 kJ/mol

- 1.00 kJ/mol

Question 55

Given:

(1) $C (s) + O_{2} (g) \to C O_{2} (g)$ , $Δ H_{1} = - 393.5 kJ$

(2) $2 CO (g) + O_{2} (g) \to 2 C O_{2} (g)$ , $Δ H_{2} = - 566.0 kJ$

Use Hess's Law to find $Δ H$ for: $2 C (s) + O_{2} (g) \to 2 CO (g)$

- 959.5 kJ

- 221.0 kJ

+ 221.0 kJ

- 172.5 kJ

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Question 56

A reaction at constant pressure releases $150 kJ$ of heat and does $30 kJ$ of work on the surroundings. What is $Δ H$ for this process?

- 120 kJ

- 180 kJ

- 150 kJ

+ 150 kJ

Question 57

Rank these liquids in order of increasing viscosity: ethanol ( $C_{2} H_{5} OH$ ), glycerol ( $C_{3} H_{5} (OH)_{3}$ ), and hexane ( $C_{6} H_{14}$ ).

A.Hexane

<

Ethanol

<

GlycerolB.Ethanol

<

Hexane

<

GlycerolC.Glycerol

<

Ethanol

<

HexaneD.Hexane

<

Glycerol

<

Ethanol

Question 58

Which of the following best describes the orientation and energy requirements for an effective collision in collision theory?

A.Any collision produces a reaction; increasing collision frequency always increases rate.B.Only collisions with energy

\geq E_{a}

AND correct geometric orientation lead to reaction.C.Orientation does not matter; only the kinetic energy of the collision is important.D.Energy is irrelevant; rate depends only on the frequency of correctly oriented collisions.

Question 59

Identify the acid-base behavior of $A l^{3 +}$ dissolved in water according to Lewis theory.

A l^{3 +}

is a Lewis base because it donates lone pairs to water.B.

A l^{3 +}

is a Lewis acid because it accepts lone pairs from water molecules.C.

A l^{3 +}

is a Brønsted–Lowry acid because it donates protons to water.D.

A l^{3 +}

has no acid-base behavior in water because it is a metal cation.

Question 60

When $Cu (s)$ is placed in $AgN O_{3} (aq)$ , which observation is consistent with this single-displacement reaction, and what does the activity series predict?

A.No reaction occurs because Cu is below Ag in the activity series.B.Silver metal deposits on the copper and the solution turns blue as Cu

^{2 +}

forms.C.Copper dissolves and forms

C u_{2} O

, a red solid.D.Silver nitrate decomposes to release

N O_{2}

gas and

O_{2}

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