Electrochemistry Extra Review Questions
1.
Given the following reaction:

 K2Cr2O7  +  SnCl2  +  HCl  --->  KCl  +  CrCl3 + SnCl4 + H2O

i) Show clearly the gain and loss of electrons that took place, and name the substances oxidized and reduced along with their agents.

ii)   Explain how you would use the loss and gain of electrons to balance the equation.

iii)  Balance the equation.

2.
Balance the following equation

I2  + NaOH  ----->  NaI  +  NaIO3  + H2O

3.


How many milliliters of 0.200 M FeSO4 are needed to reduce 50.0 mL of 0.400 M Na2Cr2O7 in an acidic solution?  The products of the reaction are Cr3+ and Fe3+.

4.
Potassium peroxydisulphate, K2S2O8, is a powerful oxidizing agent that can oxidize Cr3+ to Cr2O72- in acid solution.  In the reaction, the peroxydisulphate ion, S2O82-, is reduced to sulphate ion.  Write the balanced net ionic equation for the reaciton, and calculate the number of grams of K2S2O8 required to oxidzze the chromium in 34.0 grams of Cr(NO3)3.

5.
If you want to store a solution of nickel ion, Ni2+(aq), you should use a container made of
a)   Zn(s)
b)   Pb(s)
c)   Al(s)
d)   Mg(s)

6.
Can iodine oxidize
a) Fe2+  to  Fe3+
b) Sn to Sn
2+
 
7.
Explain why silver dissolves in 1 M nitric acid but not in hydrochloric acid.

8.
Sketch a diagram of an electrolytic cell in which a concentrated solution of NaCl is undergoing electrolysis.
a)  Label the cathode and anode, including their charges.
b)  Write half-reactions for the changes taking place at the electrodes.
c)  Write a balanced equation for the net cell reaction.

9.
At first glance, the following equation may appear to be balanced.

     MnO4-  +  Sn2+  ---->  SnO2  +  MnO2

What is wrong with it?

10.  
What current would be required to deposit 0.100 grams of nickel in 20.0 minutes from a solution of NiSO4?

11.
Experiments were performed with five metal strips, V, W, X, Y and Z, and their corresponding 1.0 mol/L nitrate solutions V(NO3)2, WNO3, X(NO3)2, Y(NO3)2 and Z(NO3)3.  A strip of metallic Y was inserted into each of the solutions and reactions were observed only in solutions containing X2+ and V2+ ions.  Metallic W reacted in solutions containing Y2+ and Z3+ ions but was not tested in the other solutions.  Metallic Z reacted in a solution of Y2+ but not in a solution of W1+.  Metallic X did not react in any of the solutions.  A list of the metals in order of decreasing strength  as reducing agents (strongest resucing agent first) is:

a)  V  W  X  Y  Z
b)  Z  Y  X  W  V
c)  W  Z  Y  V  X
d)  X  V  Z  Y  W

12.
The tarnish, AgS, on silverware articles can be removed by placing the articles in an alumnum pan and covering them with a warm solution of sodium carbonate, Na2CO3.  The following half-reactions are involved.

                          Ag2S(s)  +  2 e-  ---->   2 Ag(s)  +  S2-(aq)
 
                          Al(s)  +  3 OH1-(aq)  ---->  A(OH)3(s)  + 3 e-

The balanced net ionic equation for the total reaction is

a)   3 Ag2S(s) + 2 Al(s)  + 6 OH1-(aq) -->  6 Ag(s) + 3 S2-(aq)  + 2 Al(OH)3(s)

b)  
Ag2S(s) +  Al(s)  + 3 OH1-(aq) -->  2 Ag1+(aq)  +   S2-(aq)  +  Al(OH)3(s)  + e-
 
c)  
Ag2S(s) + 2 Al(OH)3(s)  --->  Al(s)  + 3 OH1-(aq)   +   2 Ag1+(aq)  +    S2-(aq)

d)  
Ag2S(s) + 2 Al(OH)3(s)  +  3 OH1-(aq)   --->  Al(s)  + 2 AgOH(s)   +   SO2(g)   + 2 H2O

13.
Which is the negative electrode of a nickel oxide-cadmium metal battery?

14.
Using the position of a standard reduction potential table as a guide line determine if the following reactions are spontaneous.
a)  2 Au3+  +
6 I1-  --->    3 I2   +  2 Au     
b)   3 Ca   +   2 Cr3+  --->  2 Cr +  3 Ca2+  
15.
Use an appropriate standard reduction potential table to determine the potential cell voltage for the reaction.

NO31-  +  4 H1+  +  3  Fe2+  --->  3 Fe3+  +  NO  +   2  H2O

16.
A certain amount of electricity passes through a cell in which 27.9 grams of Fe(s) is depositied from FeSO4(aq).   How much Au(s) would be desposited from the same amount of electricty passed through KAuCl4(aq)

17.
What is a Faraday?

18.
How many coulombs are passed through an electrolysis cell by
a) a current of 4.00 A for 600 seconds?
b) a current of 10.0 A for 20 minutes?
c) a current of 1.5 A for 6.00 hours?
How many Faradays correspond to the answers above?

19.
How many hours would it take to produce 25.0 grams of metallic chromium by the electrolytic reduction of Cr3+ with a current of 1.25 A?

20.
How many millilitres of 0.150 M KMnO4 solution are needed to react completely with 35.0 mL of 0.150 M SnCl2 solution, given the chemical equation for the reaction.

16 H1+ + 2 MnO41-  + 5 Sn2+  ---->  5 Sn4+  +  2 Mn2+  +  8 H2O

21.
Silver-plating, copper-plating and gold-plating (from gold(III)) are connected in series.  In one run 0.12 moles of silver is deposited.  How many moles of copper and gold are deposited at the same time?

a)  2.0 moles of Cu and 3.0 moles of Au
b)  0.12 moles of Cu and 0.12 moles of Au
c)  0.04 moles of Cu and 0.08 moles of Au
d)  0.24 moles of Cu and 0.36 moles of Au
e)  0.06 moles of Cu and 0.04 moles of Au

22.
Both calcium chloride, CaCl2, and sodium chloride are used to melt ice and snow on roads in the winter.  A certain company was marketing a mixture of these two compounds for this purpose.  A chemist, wishing to analyze the mixture, dissolved 2.651 g of it in water and precipitates the calcium by adding sodium oxalate, Na2C2O4.  

               Ca2+  +  C2O42-  --->
Na2C2O4

The calcium oxalate was then carefully filtered from the solution, dissolved in sulphuric acid, and titrated with 0.1000 M KMnO4 solution.  The reaction that occured was

6 H1+ + 5 H2C2O4  +  2 MnO41-  --->  10 CO2 + 2 Mn2+  +  8 H2O

The titration required 23.88 mL of the KMnO4 solution.

a)  How many moles of C2O42- were present in the CaC2O4 precipitate?

b)  How many grams of CaCl2 were in the original 2.651 g sample?

c)  What was the percentage of CaCl2  in the sample?

23.
Consider the following unbalanced equation

Cr2O72-(aq) + H1+(aq)  +  Br1-(aq)  ----->  Cr3+(aq)  +  Br2(aq)  +  H2O(l)

When one mole of Cr2O72-(aq) reacts according to this equation, the number of moles of Br2 produced is what?

24.
Sodium iodate reacts with sodium sulphite according to the equation

NaIO3  +  Na2SO3  ----->  Na2SO4  +  NaI                          

a)    In this reaction, which substance is the oxidizing agent?

b)    How many grams of NaIO3 are needed to react with 5.00 g of
Na2SO3