8 ELECTROLYSIS Question. 1. The electrolysis of molten calcium chloride produces
ID: 797792 • Letter: 8
Question
8
ELECTROLYSIS Question.
1. The electrolysis of molten calcium chloride produces calcium and chlorine. Write the half-reaction that takes place at the anode and the half-reaction that takes place at the cathode. Also, write the overall cell reaction for this process.
2. An electrolytic cell containing one half-cell consisting of a nickel electrode in a 1 mol/L nickel (III) chloride solution and the other half-cell consisting of a cadmium electrode in a 1 mol/L cadmium chloride solution is assembled.
(a) Sketch the cell and label the anode, the cathode, and the direction of electron flow. Be sure to include a salt bridge and a power supply in your sketch.
(b) Find the cell potential.
(c) Write the oxidation half-reaction, the reduction half-reaction and the overall cell reaction.
d) Explain how the electrolytic cell works.
3. What would be the minimum voltage to operate the following cell:
Ag(s)|Ag+(aq) || Cu2+(aq)|Cu(s)
4. Predict whether the following reactions would be spontaneous or non-spontaneous.
(a) Br2(aq) + 2 I-(aq) ?I2(aq) + 2Br -(aq)
(b) I2(aq) + 2Br -(aq) ? Br2(aq) + 2 I-(aq)
(c) Cl2(aq) + 2 I-(aq) ? I2(aq) + 2Cl- (aq)
(d) I2(aq) + 2Cl- (aq) ? Cl2(aq) + 2 I-(aq)
5. Which of the following reactions occurs spontaneously and which can only be brought about through electrolysis, assuming that all reactants and products are in their standard states? For those requiring electrolysis what is the minimum voltage required?
(a) Zn(s) + Fe2+(aq) ? Zn2+(aq) + Fe(s)
(b) 2 Fe2+(aq) + I2(s) ?2 Fe3+(aq) + 2 I-(aq)
(C) Cu(s) + Sn4+(aq) ? Cu2+(aq) + Sn2+(aq)
6. Predict the products for the electrolysis of 1 mol/L
(a) LiBr(aq)
(b) NaI (aq)
(c) CaI2(aq)
(d) NiBr2(aq)
Please explain and shows the steps. thanks.
Explanation / Answer
1. Anode half reaction
........ 2 Cl - ---> Cl2 + 2e-
Cathode half reaction
........ [Ca 2+] + 2e- ----> Ca
Overall cell reaction
........[Ca2+] + 2 Cl- -----> Ca + Cl2
2. Standard electrode potentials of Cadmium and nickel are -0.40 and -0.25 respectively.
So Cadmium is the anode and Nickel is the cathode .
E0 cell = Eo cathode - E0 anode
=-0.25 -(-0.40)
=0.15 V
Cell notation is ;
Cd(s)|Cd+2(aq) || Ni+2(aq)|Ni(s)
Anode Half reaction is :
Cd --------> Cd+2 + 2e-
Cathode half reaction :
Ni+2 + 2e- -----> Ni
Overall reaction ;
Cd + Ni+2 ----------> Cd+2 + Ni
according to nearnst equation
E= Eo - (0.059 /n) log K
=Eo -(0.059 /2) * log [Cd+2] / [Ni+2]
=0.15 - (0.059/2) * log 1/1
=0.15-0
=0.15
Cell potential is 0.15
Electrolytic cell fuctioning :
Electrolytic cells are composed of a vessel used to do electrolysis, containing electrolyte, usually a solution of water or other solvents capable of dissolving various ions into solution, and a cathode and anode. The electrolyte in the cell is inert unless driven by external voltage into a redox reaction with the anode and cathode. The term literally means a cell that splits up or loosens ions.
3) Given Ag(s)|Ag+(aq) || Cu2+(aq)|Cu(s)
For a reaction to be spontaneous Potential of the cell should be positive .
So the reaction will for all values of E> 0
4)
(a) Br2(aq) + 2 I-(aq) ?I2(aq) + 2Br -(aq) ---------------- spontaneous
(b) I2(aq) + 2Br -(aq) ? Br2(aq) + 2 I-(aq)--------------- non -spontaneous
(c) Cl2(aq) + 2 I-(aq) ? I2(aq) + 2Cl- (aq)------------------ spontaneous
(d) I2(aq) + 2Cl- (aq) ? Cl2(aq) + 2 I-(aq)--------------- non spontaneous
5)
(a) Zn(s) + Fe2+(aq) ? Zn2+(aq) + Fe(s)
E0 must be positive for a reaction to be spontaneous
Eo cell = Eo cathode - Eo anode
=-0.44 - (-0.76)
=0.32
So the reaction is spontaneous
(b) 2 Fe2+(aq) + I2(s) ?2 Fe3+(aq) + 2 I-(aq)
Eo cell = 0.54 - 0.77
E0cell = -0.23
So the reaction is not spontaneous
(C) Cu(s) + Sn4+(aq) ? Cu2+(aq) + Sn2+(aq)
Eo cell = 0.15 - 0.16
= - 0.01
so the reaction is not spontaneous
(a) LiBr(aq)
LiBr --------> Li+ + Br-
(b) NaI (aq)
NaI -------> Na+ + I-
(c) CaI2(aq)
CaI2 ---------------> Ca+2 + 2 I-
(d) NiBr2(aq)
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