Honors Chemistry

Chapter 18 Study Questions

 

1. Calculate the oxidation number for nitrogen in the following substances:

a) NH3 b) N2 c) NO2 d) NO3-

 

2. In the oxidation-reduction reaction,

Br2(l) + 2 I-(aq) 2 Br-(aq) + I2(s),

a) which substance is being reduced?

b) which element is increasing in oxidation number?

c) which element is gaining electrons?

d) which substance is the oxidizing agent?

e) which substance is the reducing agent?

 

3. Classify each of the following substances as an oxidizing agent, reducing agent or both. List the oxidizing agents in order of decreasing strength; list the reducing agents in order of decreasing strength (use Eo Table):

Ni(s), H+(aq), Au(s), Cl2(g), Sn2+(aq), Mg(s), Fe2+(aq)

 

4. For each of the following reactions: 1) identify the oxidation and reduction half-equations, and 2) balance the equation (adding H+ and H2O as needed), 3) find Eo (in volts) and 4) determine whether the reaction is spontaneous under standard conditions.

a) Ag(s) + Cu2+(aq) Ag+(aq) + Cu(s)

b) Ni(s) + MnO4-(aq) Ni2+(aq) + Mn2+(aq)

c) Mn2+(aq) + NO3-(aq) MnO2(s) + NO(g)

 

5. For each of the following reactions: 1) find Eo (in volts) and 2) determine whether the reaction is spontaneous under standard conditions.

a) the reaction between iron and iron(III) ions to give iron(II) ions.

b) the following cell: I- | I2 || Zn2+ | Zn

 

6. Which of the following ions will oxidize Br- ion to Br2?

a) Pb2+ b) H+ c) Au3+ d) MnO4-

 

7. A voltaic cell has an aluminum electrode in Al2(SO4)3 solution in one compartment and the other compartment has a lead electrode in PbSO4 solution.

a) Which has a greater tendency to be oxidized, Al or Pb? Write a balanced equation for the spontaneous reaction.

b) Draw a diagram of the voltaic cell, including

1. the anode and cathode

2. the direction of flow of electrons, positive ions and negative ions

c) Which electrode will increase in mass?

 

8. The following table contains data obtained by measuring the voltage between two metals in an experiment like the one you did with a lemon:

 

Voltaic Cell

Anode (-)

Cathode (+)

Cell Voltage (v)

Pb/Ni

Ni

Pb

0.10 volts

Pb/Au

Pb

Au

0.80 volts

Pb/Fe

Fe

Pb

0.25 volts

Ni/Au

Ni

Au

0.90 volts

Ni/Fe

Fe

Ni

0.15 volts

Fe/Au

Fe

Au

1.05 volts

 

a) From the data in the table above, which metal is the strongest reducing agent?

b) From the data in the table above, which metal is the weakest reducing agent?

c) Using the reduction of lead (Pb) as a reference, construct a half-cell voltage table from the experimental data above.

 

 

 

 

 

Summary of Chapter 18: Electrochemistry

 

definitions from Chapter 4

oxidation and reduction

oxidizing and reducing agents

oxidation number

oxidation-reduction reactions

balancing oxidation-reduction reactions

voltaic cells

anode and cathode

direction of electron and ion flow

porous barrier/salt bridge

standard voltages: Eoox and Eored

applications of values for Eo:

calculation of cell voltage (Eo)

reaction spontaneity

strength of oxidizing and reducing agents

electrolytic cells