Regents Review 1

Reduction-Oxidation [REDOX]Notes

1. Given the reaction: 2 Al(s) + Fe 2 O 3 (s)Which species undergoes reduction?

(1)A1 (3)A13

(2)Fe (4)Fe3

Al2O3(s) + 2Fe(s)

2. Which change in oxidation number indicates oxidation?(1) -1 to +2 (3) +2 to -3(2) -1 to -2 (4) +3 to +2

3. Which particles are gained and lost during a redox reaction?(1) electrons (3) neutrons(2) protons (4) positrons

4. Given the redox reaction: Cr3+ + Al -»Cr + Al3+

As the reaction takes place, there is a transfer of(1) electrons from Al to Cr3"*(2) electrons from Cr 3Mo Al(3) protons from Al to Cr34

(4) protons from Cr 3+to Al

5. A diagram of a chemical cell and an equation are shown below.

Pb(sH -Cu(s)

Pb(s) + Cu2 Pb2 +(aq) + Cu(s)

When the switch is closed, electrons will flow from(l)fhePb(s)totheCu(s)(2) the Cu(s) to the Pb(s)(3) the Pb 2+ (aq) to the Pb(s)(4)theCu2+(aq)totheCu(s)

6. Given the reaction for the corrosion of aluminum: 4A1 + 3 O 2 — » 2 A l 2 C * 3Which half-reaction correctly represents the oxidation that occurs?

(l)Al + 3e~->-Al3+

(2) Al ->A1 3+ + 3e "

Regents Review 2

7. Which energy transformation occurs when an electrolytic cell is in operation?(1) chemical energy —^electrical energy(2) electrical energy -^chemical energy(3) light energy —>heat energy(4) light energy ->chemical energy

8. The diagram below shows a key being plated with copper in anelectrolytic cell.

CuSO4(a

Copper Batteryelectrode

Given the reduction reaction for this cell: Cu 2 + (aq) + 2e~ ->Cu(s)This reduction occurs at

(1) A, which is the anode(2) A, which is the cathode(3) B, which is the anode(4) B, which is the cathode

9. Which half-reaction can occur at the anode in a voltaic cell?

(2) Sn + 2e " -»Sn 2+ (4) Fe3H ->Fe 2+ + e

10. What is the oxidation number of chromium in K 2 Cr 2 O 7 ?(1) +12 (3) +3(2)+2 (4)+6

11. Which process requires an external power source?(1) neutralization (3) fermentation(2) synthesis (4) electrolysis

12. Given the reaction:Mg(s) + 2 H + (aq) + 2 Cl (aq) -> Mg 2+ (aq) + 2 Cl ~ (aq) + H2 (g)Which species undergoes oxidation?

(l)Mg(s) (3)Cl-(aq)(2)H + (aq) (4)H2(g)

13. Which reaction is an example of an oxidation-reduction reaction?(1) AgNO 3 + KI -»AgI + KNO 3(2) Cu + 2 AgNO 3 ->Cu(NO 3 ) 2 + 2 Ag

(4) Ba(OH)2 + 2 HC1 ->BaCl 2 + 2 H 2 O

14. In which substance does chlorine have an oxidation number of+1?(1)C12 (2)HC1 (3)HC1O (4)HC1O2

Regents Review 3

15. Which statement is true for any electrochemical cell?(1) Oxidation occurs at the anode, only.(2) Reduction occurs at the anode, only.(3) Oxidation occurs at both the anode and the cathode.(4) Reduction occurs at both the anode and the cathode.

16. Which half-reaction correctly represents reduction?(1) Ag-»Ag++e~ (3)Au3+ + 3e

17. What is the purpose of the salt bridge in a voltaic cell?(1) It blocks the flow of electrons.(2) It blocks the flow of positive and negative ions.(3) It is a path for the flow of electrons.(4) It is a path for the flow of positive and negative ions.

18. A voltaic cell differs from an electrolytic cell in that in a voltaic cell(1) energy is produced when the reaction occurs(2) energy is required for the reaction to occur(3) both oxidation and reduction occur(4) neither oxidation nor reduction occurs

19. In a redox reaction, how does the total number of electrons lost by theoxidized substance compare to the total number of electrons gained by thereduced substance?

(1) The number lost is always greater than the number gained.(2) The number lost is always equal to the number gained.(3) The number lost is sometimes equal to the number gained.(4) The number lost is sometimes less than the number gained.

20. Given the equation: 2 Al + 3 Cu 2+ -»2 Al3+ + 3 CuThe reduction half-reaction is

(l)Al->A!3+ + 3e^ (3)Al + 3e--»Al3+

2 +2e~->>Cu (4)Cu2+->Cu

Base your answers to questions 21 through 23 on the diagram of a voltaic cell and on yourknowledge of chemistry.

Voltaic Cell

Wire /TT\e21. On the diagram, indicate with one or more

arrows the direction of electron flow throughthe wire. [1]

Copperstrip

22. Write an equation for the half-reaction thatoccurs at the zinc electrode. [1]

23. Explain the function of the salt bridge. [1]

Regents Review 4

Base your answers to questions 24 through 29 on the following redox reaction, which occursspontaneously in an electrochemical cell.

Zn + Cr3+-*Zn2+ + Cr

24. Write the half-reaction for the reduction that occurs. [1]

25. Write the half-reaction for the oxidation that occurs. [1]

26. Balance the equation using the smallest whole-number coefficients. [1]

_Zn + Cr * -» Zn 2+ + Cr

27. Which species loses electrons and which species gains electrons? [1]

loses electrons.

j*ains electrons.

28. Which half-reaction occurs at the cathode? [1]

29. State what happens to the number of protons in a Zn atom when it changes to Zn 2+ as the redoxreaction occurs. [1]

Base your answers to questions 30 through 32 on the diagram below, which represents a voltaic cellat 298 K and 1 arm.

VoltmeterWire

Pb electrode —

Half-cell 1 —

Switch S

Zn electrode

— Half-cell 2

Pb^aq) + Zn-» Pb + Zn^aq)30. In which half-cell will oxidation occur when switch S is closed? [1]

31 Write the balanced half-reaction equation that will occur in half-cell 1 when switch S is closed.[1]

32. Describe the direction of electron flow between the electrodes when switch S is closed. [1]

Regents Review 5

Base your answers to questions 33 and 34 on the unbalanced redox reaction below.Cu(s) + AgNO 3 (aq) ->Cu(NO 3 ) 2 (aq) + Ag(s)

33. Write the reduction half-reaction. [1]

34. Balance the redox equation, using the smallest whole-number coefficients. [1]

Cu(s) + AgNO 3 (aq) -» Cu(NO 3 ) 2 (aq) + Ag(s)

Base your answers to questions 35 through 37 on the diagram of the voltaic cell below.Voltaic Cell

Wire—

Pb(s) electrode—

Switch^*

Ag(s) electrode

Half-cell 1 Half-cell 2

2 Ag*(aq) + Pb(s) — * Pb2*(aq) + 2 Ag(s)

35. When the switch is closed, in which half-cell does oxidation occur? [1]

36. When the switch is closed, state the direction that electrons will flow through the wire. [1]

37. Based on the given equation, write the balanced half-reaction that occurs in half-cell 1. [1]

The outer structure of the Statue of Liberty is made of copper metal. The framework is madeof iron. Over time, a thin green layer (patina) forms on the copper surface.

38. When copper oxidized to form this patina layer, the copper atoms became copper(II) ions (Cu 2+).Write a balanced half-reaction for this oxidation of copper. [1]

39. Where the iron framework came in contact with the copper surface, a reaction occurred in whichiron was oxidized. Using information from Reference Table J, explain why the iron was oxidized. [1]