Exam #4

Question 1

In the redox reaction: Zn + Cu²⁺ → Zn²⁺ + Cu, which species is reduced?

A) Zn

B) Cu

C) Zn²⁺

D) Cu²⁺

Answer 1

D) Cu²⁺

Question 2

Which of the following is the oxidizing agent in the reaction: 2Fe³⁺ + 2I⁻ → 2Fe²⁺ + I₂?

A) Fe³⁺

B) Fe²⁺

C) I⁻

D) I₂

Answer 2

A) Fe³⁺

Question 3

When balancing a redox reaction in acidic solution, what must be added to balance oxygen atoms?

A) H⁺

B) H₂O

C) OH⁻

D) e⁻

Answer 3

B) H₂O

Question 4

Which part of a galvanic cell is the site of oxidation?

A) Anode

B) Cathode

C) Salt bridge

D) Voltmeter

Answer 4

A) Anode

Question 5

In a galvanic cell, which direction do electrons flow?

A) From cathode to anode

B) From anode to cathode

C) Both directions

D) No flow

Answer 5

B) From anode to cathode

Question 6

A reduction potential of +1.23 V means the substance:

A) Is easily oxidized

B) Is a strong reducing agent

C) Is likely to be reduced

D) Is neutral

Answer 6

C) Is likely to be reduced

Question 7

If E°(cathode) = +0.80 V and E°(anode) = +0.34 V, what is the cell potential?

A) +1.14 V

B) +0.46 V

C) -0.46 V

D) -1.14 V

Answer 7

B) +0.46 V

Question 8

Which of the following affects the rate constant (k) in the rate law equation?

A) Concentration

B) Catalyst

C) Temperature

D) Both temperature and catalyst

Answer 8

D) Both temperature and catalyst

rate increases, but rate constant remains the same in concentration

Question 9

If doubling the concentration of A doubles the rate, the order of the reaction with respect to A is:

A) Zero

B) First

C) Second

D) Cannot be determined

Answer 9

B) First

Question 10

What is the half-life formula for a first-order reaction?

A) t½ = 0.693/k

B) t½ = [A]₀/2k

C) t½ = k/[A]₀

D) t½ = 2k

Answer 10

A) t½ = 0.693/k

Question 11

Which of the following statements about catalysts is true?

A) They are consumed in the reaction

B) They decrease the rate of reaction

C) They lower activation energy

D) They increase equilibrium constant

Answer 11

C) They lower activation energy

Question 12

In the reaction mechanism: A → B → C, B is:

A) Reactant

B) Product

C) Intermediate

D) Catalyst

Answer 12

C) Intermediate

Question 13

What is the reducing agent in the reaction: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂?

A) Cl₂

B) Br⁻

C) Cl⁻

D) Br₂

Answer 13

B) Br⁻

Question 14

In acidic solution, which of the following is needed to balance hydrogen atoms in a redox reaction?

A) OH⁻

B) H₂

C) H⁺

D) H₂O

Answer 14

C) H⁺

Question 15

Which of the following statements is true about a galvanic cell?

A) Electrons flow from cathode to anode

B) The cathode is negatively charged

C) The anode loses mass during the reaction

D) The salt bridge provides electrons

Answer 15

C) The anode loses mass during the reaction

Question 16

Which component prevents charge buildup in a galvanic cell?

A) Voltmeter

B) Salt bridge

C) Electrodes

D) Power source

Answer 16

B) Salt bridge

Question 17

Which of the following would be oxidized based on standard reduction potentials?

A) A species with +0.13 V

B) A species with +0.34 V

C) A species with -0.13 V

D) A species with +1.23 V

Answer 17

C) A species with -0.13 V

Question 18

Electrolysis requires an external power source because the reaction is:

A) Spontaneous

B) Endergonic

C) Exothermic

D) Rapid

Answer 18

B) Endergonic

Question 19

During electrolysis of molten NaCl, what is produced at the cathode?

A) Na⁺

B) Na metal

C) Cl₂ gas

D) H₂ gas

Answer 19

B) Na metal

Question 20

Q: A reaction is second order with respect to A. If [A] is tripled, the rate increases by a factor of:

A) 2

B) 3

C) 6

D) 9

Answer 20

D) 9 (3^2 = 9)

Question 21

In a first-order reaction, if the initial concentration of reactant is 1.0 M and after 1 half-life it’s 0.50 M, how much remains after 3 half-lives?

A) 0.25 M

B) 0.125 M

C) 0.0625 M

D) 0.50 M

Answer 21

B) 0.125 M

Question 22

A galvanic cell is constructed with a zinc electrode in Zn²⁺ solution and a copper electrode in Cu²⁺ solution. The standard reduction potentials are: Zn²⁺/Zn = -0.76 V, Cu²⁺/Cu = +0.34 V. What is the standard cell potential, and which metal is oxidized?

A) 1.10 V; Cu is oxidized

B) 0.42 V; Cu is oxidized

C) 1.10 V; Zn is oxidized

D) -1.10 V; Zn is oxidized

Answer 22

C) 1.10 V; Zn is oxidized

Question 23

A student measures the voltage of a galvanic cell as lower than the calculated standard potential. Which is a likely explanation?

A) The temperature is higher than standard conditions

B) The salt bridge is broken

C) The concentrations of reactants are lower than 1 M

D) The anode is larger than the cathode

Answer 23

C) The concentrations of reactants are lower than 1 M

Question 24

During the electrolysis of water, twice as much hydrogen gas is produced compared to oxygen. Why?

A) Hydrogen has a lower molar mass

B) Hydrogen is produced at a faster rate

C) Two moles of H⁺ are needed for every mole of O²⁻

D) Water has more hydrogen than oxygen

Answer 24

C) Two moles of H⁺ are needed for every mole of O²⁻

Question 25

You conduct an experiment and find that doubling [A] while holding [B] constant causes the rate to quadruple. What is the order of the reaction with respect to A? A) Zero B) First C) Second D) Third

Answer 25

C) Second

Question 26

A reaction has the rate law Rate = k[A][B]². If [A] is cut in half and [B] is doubled, how does the rate change? A) Increases by a factor of 2 B) Stays the same C) Decreases by a factor of 2 D) Increases by a factor of 4

Answer 26

A) Increases by a factor of 2

Question 27

You increase the temperature of a reaction mixture. What happens to the rate constant (k) and activation energy (Ea)? A) k increases, Ea increases B) k decreases, Ea increases C) k increases, Ea stays the same D) k increases, Ea decreases

Answer 27

A) k increases, Ea increases

Question 28

You are studying a two-step reaction. Step 1 is fast and reversible. Step 2 is slow. Which determines the overall rate law? A) Step 1 B) Step 2 C) The equilibrium constant of step 1 D) The final product concentration

Answer 28

B) Step 2

Question 29

The standard reduction potentials are: Fe³⁺/Fe²⁺ = +0.77 V and Cu²⁺/Cu = +0.34 V. What is the standard cell potential for Fe³⁺ + Cu → Fe²⁺ + Cu²⁺? A) +0.43 V B) -0.43 V C) +1.11 V D) -1.11 V

Answer 29

A) +0.43 V (subtract oxidized from reduced)

Question 30

A galvanic cell has a standard potential of 1.10 V. Under non-standard conditions at 25°C, the concentration of products is 1.0 M and reactants is 0.010 M. The reaction involves 2 electrons transferred. What is the cell potential under these conditions? Constants: R = 8.314 J/mol·K F = 96,485 C/mol·e⁻ A) 1.04 V B) 1.16 V C) 0.94 V D) 0.88 V

Answer 30

A) 1.04 V