1|Additional Questions Chapter 10 Electrochemistry SK026
1
a)
Consider the following observations,
Half cell 1: aluminium electrode dissolved to produce aluminium ion.
Half cell 2: silver metal deposited at silver electrode.
i.
ii.
iii.
iv.
2
Write an half-reaction that occurred at each electrode.
Write a balanced equation for the overall reaction.
Calculate cell voltage at 25 ºC if the concentration of silver ion is 1.00 M and
concentration of the aluminium ion is 0.36 M.
[Eº(Al3+/Al) = -1.676 V; [Eº(Ag+/Ag) = +0.800V]
Will the reaction proceed spontaneously?
[7 marks]
b)
Calculate the mass of magnesium produced in 4.00103s from the electrolysis of
molten MgCl2, if the electrical current of 60.00 A is passed through.
[3 marks]
a)
The following diagram shows an arrangement of an electrochemical cell created
constructed two half-cells A and B.
[ E Zn 2 |Zn = 0.76 V; E Ag  |Ag = +0.80 V]
Salt bridge
V
Zinc
Silver
Zn2+(aq)
Ag+(aq)
A
i.
ii.
iii.
b)
i.
ii.
B
Write the overall chemical equation of the redox reaction.
Calculate the standard electromotive force cell E°cell under standard
condition.
If the concentration of Zn2+ solution is maintained at 1.0 mol dm3 and the
voltage of the cell is 1.21 V at 25C, calculate the concentration of silver ion
in the B half-cell.
[5 marks]
Write the reaction equations involved at the anode and the cathode for
an electrolysis of aqueous Na2SO4.
How many grams of aluminium can be formed if a 305 coulomb of electric
current is passed through an electrolytic cell containing molten aluminium
salt?
[5 marks]
2|Additional Questions Chapter 10 Electrochemistry SK026
3
a)
A galvanic cell is constructed with two half-cells; Sn/Sn2+ and Zn/Zn2+. The halfcells are connected by a salt-bridge.
[ ESn 2 |Sn = 0.14 V; E Zn 2 |Zn = 0.76 V]
i.
ii.
4
Write the half equation at the anode and the cathode and the overall cell
equation.
[3 m]
2+
If the concentration of Sn is 0.10 M and the value of Ecell is 0.63 V at 25 ºC,
calculate the concentration of Zn2+.
[3 marks]
State the Faraday’s first law.
[1 marks]
How many faradays are required to produce 1.98 L of chlorine gas, Cl2 at
0.987 atm and 20 ºC from molten sodium chloride, NaCl?
[3 marks]
b)
i.
ii.
a)
For the following reaction,
2Cr (s) + 3Pb2+ (aq) →
2Cr3+ (aq) + 3Pb (s)
Calculate the cell potential of a Daniel cell at 25oC, if the concentrations of
Pb2+(aq) and Cr3+(aq) are 0.20 M and 0.35 M, respectively.
[ Eo Pb2+/ Pb = -0.13 V ; Eo Cr3+/Cr = -0.74 V]
[5 marks]
5
b)
In an electrolysis, a current of 2.50 A flowed through an aqueous solution of
copper (II) sulphate, CuSO4 for 3.00 hours. Calculate the volume of O2 collected if
the electrolysis was carried out at STP.
[5 marks]
a)
Consider the following redox reactions:
Mg (s) + Sn2+ (aq)
Cl2 (g) + 2Ag (s)
Sn (s) + 2Ag+ (aq)
i.
ii.
iii.
Mg2+ (aq) + Sn (s)
2Cl- (aq) + 2Ag+ (aq)
Sn2+ (aq) + 2Ag (s)
State the strongest reducing agent.
Identify the oxidising agent in each reaction.
Arrange the oxidizing agents in order of decreasing strength.
[ E Mg 2 |Mg = 2.37 V; ESn 2 |Sn = 0.14 V; EAg |Ag = +0.80 V; E Cl |Cl- = +1.36 V]
2
[5 marks]
b)
A galvanic cell consists of a lead anode immersed in a 1.00 M solution of
Pb(NO3)2 and a platinum cathode that has gaseous hydrogen bubbling over it at
a pressure of 1.00 atm. The hydrogen ion concentration of the solution is
1.30 x 10-5 M.
i.
Write the cell notation for this reaction.
ii.
Calculate the cell potential, Ecell.
iii.
Predict the spontaneity of the reaction.
[ EPb2 |Pb = 0.13 V; E  H |H = +0.00 V]
2
[5 marks]
3|Additional Questions Chapter 10 Electrochemistry SK026
6
a)
FIGURE 1 shows the apparatus used for determining the standard reduction potential
for the system Fe2+(aq) / Fe(s) at 25 oC.
e
v
B
A
C
D
FIGURE 1
i.
ii.
iii.
7
8
Identify A, B, C and D. State the relevant conditions.
Write the balanced equation for the cell reaction.
If the voltmeter reading is 0.44 V, what is the standard reduction potential of
Fe2+(aq) / Fe(s) ?
[6 marks]
b)
The electrolysis of a sodium sulphate solution produces 0.84 L of O2 at 1 atm and
25 oC. Calculate the number of Faradays required for the process.
[4 marks]
a)
Predict the products of the electrolysis of an aqueous solution of sodium chloride in a
cell using platinum electrodes. Give reasons.
[4 marks]
b)
A current of 10.0 A is passed through a solution of chromium (III) chloride, CrCl3,
for 30 minutes. Determine the mass of chromium deposited at the cathode.
[6 marks]
a)
A galvanic cell S, is made up by immersing zinc metal in x M Zn2+ solution and
copper metal in 0.25 M Cu2+ solution. The two half cells were connected by a salt
bridge.
[ E Zn 2 |Zn = 0.76 V; ECu2 |Cu = +0.80 V]
(i)
(ii)
(iii)
(iv)
(b)
State the function of the salt bridge in cell S.
Write the cell notation for galvanic cell S.
Calculate the concentration of Zn2+ ion in the solution at 25°C if the cell
potential is +1.075 V.
Suggest one method to increase the cell potential of cell S.
[6 marks]
An aqueous solution of copper (II) sulphate, CuSO4 is electrolysed using platinum
electrodes. During the electrolysis, a current of 2.50 A was passed through the
solution for 2.00 hours.
(i)
Write the reaction equations involved at the anode and cathode.
(ii)
Calculate the amount of oxygen gas collected in mole.
[4 marks]
4|Additional Questions Chapter 10 Electrochemistry SK026
9
(a)
The overall equation for a galvanic cell is shown below:
2Ag+(aq) + Ni(s)
(i)
(ii)
10
Write the half equation at the anode and the cathode.
Calculate the concentration of Ag+ at 25oC when [Ni2+] = 1.00 x 10-4 M and
Ecell = 1.17 V.
[Eocell = 1.06 V]
[4 marks]
(b)
A current of 1.88 x 105 ampere is passes through molten magnesium chloride in an
electrolytic cell for 24 hours. Calculate the mass (in kg) of magnesium formed if the
cell is 89% efficient.
[6 marks]
a)
A cell notation of a galvanic cell is as follows:
Zn (s)  Zn2+ (aq, 1.0 M)  Sn2+ (aq, 1.0 M)  Sn (s)
i.
ii.
iii.
iv.
11
Ni2+(aq) + 2Ag(s)
Write the overall call equation.
Identify the oxidizing agent.
Calculate the standard cell potential.
Calculate the concentration of Zn2+ solution if the concentration of Sn2+
solution is 0.15 M and the value of Ecell is 0.61 V at 25 oC and 1.0 atm.
[Given: Eo Zn2+Zn = ─0.76 V, Eo Sn2+Sn = ─0.14 V]
[7 marks]
b)
Calculate the mass of calcium deposited at the cathode if an electric current of
3.5 A is passed through in an electrolysis of molten calcium bromide, CaBr2,
for 1 hour by using inert electrodes.
[3 marks]
(a)
The cell potential for the following electrochemical cell at 25 oC is 1.48 V.
Zn(s)  Zn2+ (aq, 1.0 M)  Ag+ (aq, x M)  Ag(s)
(i)
(ii)
(iii)
(b)
Write the overall cell equation.
Calculate the standard electrode potential, Eocell.
Calculate the concentration of Ag+ ion in the cell.
[Given: E o Zn 2 /Zn   0.76 V, E o Ag /Ag   0.80 V ]
[5 marks]
Electrolysis of water at room temperature yielded oxygen gas at platinum anode by
using current of 0.30 A for 30 minutes. Calculate the volume of oxygen gas
produced in this electrolysis.
[5 marks]
5|Additional Questions Chapter 10 Electrochemistry SK026
12
(a)
Given the cell notation below at 25oC:
R(s)  R2+ (aq, 0.01 M)  S2+ (aq, x M)  S(s)
(i)
(ii)
(iii)
(iv)
Write a balanced equation for the above reaction.
Calculate Eocell.
Given the Ecell is +017 V, calculate the concentration of S2+.
If the temperature of the cell is increased, would the value of Ecell be greater
or less than +0.17 V? Explain.
[ E  R 2 |R = 0.25 V; E S2 |S = −0.13 V]
[6 marks]
(b)
By using the information in TABLE 3, explain why chlorine oxidises Fe2+ to Fe3+
but iodine does not.
TABLE 3
Half reaction
Cl2 + 2e
Fe3+ + e
I2 + 2e
-
2Cl
Fe2+
2I-
Eo / V
+1.36
+0.77
+0.54
[2 marks]
(c)
Copper metal is produced when 500 coulomb of electricity are used in the
electrolysis of molten copper (II) sulphate. Calculate the number of moles of copper
deposited.
[2 marks]