CHAPTER 19- Practice Exercise Dr. PAHLAVAN
Electrochemistry
Problem #1. Balance each of the following equations, identify the substance acting as oxidizing or reducing agent.
Identify the oxidation half and reduction half reactions.
a) MnO4-(aq) + H2O2(aq) à Mn2+(aq) + O2(g) (acidic solution) b) S2O32-(aq) + I2(aq) à SO42-(aq) + I-(aq) (basic solution)
c) HSO3-(aq) + NO3-(aq) à HSO4-(aq) + NO(g) (acidic) d) Ag2S(s) + NO3-(aq) àAg+(aq) + S(s) + NO(g) (basic) e) Br2(l) + AsO2-(aq) à Br-(aq) + AsO43-(aq) (acidic) f) MnO4 – (aq) + Mn 2+ (aq)à MnO2 (s)
g) IO3 – (aq)+ I – (aq)+ Cl – (aq)à ICl2 (g)
Problem #2. Given the following data:
E0red
Ca2+(aq) + 2e- à Ca(s) -2.87 v
Zn2+(aq) + 2e- à Zn(s) -0.76 v
Co2+(aq) + 2e- à Co(s) -0.28 v
Sn2+(aq) + 2e- à Sn(s) -0.14 v
Pb2+(aq) + 2e- -à Pb(s) -0.13 v
Arrange the metals in order of increasing oxidation under standard state conditions.
Problem #3. Consider the following half reactions:
Na+(aq) + e- à Na(s) , E0red = -2.71 v
Zn2+(aq) + 2e- à Zn(s) , = -0.76 v
Fe2+(aq) + 2e- à Fe(s) , = -0.44 v
a) which one is the most active metal? b) which one is the most oxidizing agent? c) which one oxidized the best?
Problem #4. Given the following E0 values at 250C.
Fe2+ + 2e- à Fe E0red = -0.44 v , Sn2+ + 2e- à Sn E0red = -0.14 v
Determine if the following reaction is spontaneous. Fe2+ + Sn à Fe + Sn2+ .
Also, identify the anode and the cathode for the reaction that spontaneously occurs.
Problem #5. A voltaic cell is to be designed at standard state conditions using the
following two half- reactions.
Mn2+(aq) + 2e- à Mn(s) E0red = -1.18 v , Cr3+(aq) + 3e- à Cr(s) E0red = -0.74 v
a) Write chemical equation describing the spontaneous cell reaction and calculate E0cell.
b) Draw a figure representing the voltaic cell, using these reactions. Label all components and indicate the direction of e- flow.
Problem #6. Calculate E0 for the following unbalanced reactions. Indicate if the reactions are spontaneous as
written.
a) Al3+(aq) + Mg(s) à Al(s) + Mg2+(aq) b) ClO4-(aq) +Mn2+(aq) + H2O(l) à MnO4-(aq) + H+(aq) + ClO3-(aq)
Given data:
Al3+ + 3e- à Al E0red = -1.66 v
Mg2+ + 2e- à Mg = -2.37 v
MnO4- + 8H+ +5e- à Mn2+ + 4H2O = 1.51 v
ClO4- + 2H+ +2e- à ClO3- + H2O = 1.19 v
Problem #7. Calculate DG0, K, and E at 298 K for the reaction, 2Br -(aq) + Cl2(g) à Br2(l) + 2Cl -(aq)
given E0= 0.300 v and the following concentrations: [Br -]= 0.10 M , PCl2 = 0.50 atm , and [Cl-] =0.010 M.
Problem #8. Calculate the voltage generated by a hydrogen-concentration cell utilizing the following
concentrations: H2(2 atm) + 2H+(0.1 M) ßà H2(0.5 atm) + 2H+(0.5M)
A concentration cell involves a reaction having the same reactants as products, but with differing concentrations. In which direction is the reaction spontaneous?
Problrm #9. Given the following data:
Fe2+ + 2e- à Fe E0red = -0.44 v , Ag+ + e- à Ag E0red = 0.80 v
Answer the following questions with respect to the reaction ; Fe2+(aq) + 2 Ag(s) à Fe(s) + 2 Ag+(aq)
a) what is E0 for the reaction? b) is the reaction spontaneous at standard state conditions?
c) what is the value of E at equilibrium? d) what is the value of equilibrium constant at 250C ?
e) if [Fe2+]=0.100 M and [Ag+] = 0.0100 M , what is the magnitude of E at 250C?
Problem #10. Given the following reaction, 2 Al(s) + 3 Mn2+(aq) à 2 Al3+(aq) + 3 Mn(s)
what is the concentration of Al3+ if E0cell = 0.48 v , Ecell = 0.47 v and the concentration of Mn2+ is 0.49 M at 250C?
Problem #11. Given that K = 3.76x1014 for the reaction; 2 Fe3+(aq) + Cu(s) à 2 Fe2+(aq) + Cu2+(aq)
at 250C, what is the E0 for the reaction?
Problem #12. Given the following data:
Ag+ + e- à Ag E0red = 0.80 v , Al3+ + 3e- à Al E0red = -1.66 v
a) what is E0cell for a voltaic using the two half-reactions at 250C?
b) what is Ecell if [Ag+] = 0.50 M and [Al3+] = 1.0 M at 250C?
c) what is K for the reaction at 250C?
Problem #13. Given the following data:
Fe2+(aq) + 2e- à Fe(s) E0red = -0.44 v , Cr3+(aq) + e- à Cr2+(aq) E0red = -0.407 v
Answer the following questions:
a) What is the spontaneous cell reaction when a voltaic cell is constructed using these two half- reactions?
b) What is the E0 for the reaction? c) What is equilibrium constant and DG0?
d) If the concentration of Cr3+ and Cr2+ are each 0.10 M and the cell potential is 0.100 v, what is the concentration of
Fe2+?
e) What is E for the reaction at equilibrium?
Problem #14. How many grams of cadmium are consumed in a nickel-cadmium battery if it operates at a constant current of 0.20 amp for 30.00 sec? The half-reaction of interest is; Cd (s) + 2 OH-(aq) à Cd(OH)2(s) + 2e-
Problem #15. How long must a current of 5.00 A be applied to a solution of Ag + to produce 10.5 g silver metal?
Problem #16. Consider a current of 10.0 amps is passed for 30.0 minutes through a solution containing Cu2+. Calculate a) quantity of charge in coulombs b) number of moles of electrons
c) number of moles of copper metals d) grams mass of copper that is plate out
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