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# Electrochemistry and balancing redox equations

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Electrochemistry Part III

1- Balance each redox reaction occurring in acidic aqueous solution. Express your answer as a chemical equation. Identify all of the phases in your answer.

Ni(s)+Cd 2+ (aq)→Ni 2+ (aq)+Cd(s)
Ni(s)+Cd 2+ (aq)→Ni 2+ (aq)+Cd(s)
MnO 4 − (aq)+Al(s)→Mn 2+ (aq)+Al 3+ (aq)

2- Balance each redox reaction occurring in basic aqueous solution.

MnO − 4 (aq)+Br − (aq)→MnO 2 (s)+BrO − 3 (aq)
Ag(s)+CN − (aq)+O 2 (g)→Ag(CN) − 2 (aq)
O − 2 (aq)+Al(s)→NH 3 (g)+AlO − 2 (aq)

3- Calculate the standard cell potential (E ∘ ) for the reaction X(s)+Y + (aq)→X + (aq)+Y(s) if K = 5.82×10−3.Express your answer to three significant figures and include the appropriate units.

4- Calculate the standard free-energy change at 25 ∘ C for the following reaction: Mg(s)+Fe 2+ (aq)→Mg 2+ (aq)+Fe(s) Express your answer to three significant figures and include the appropriate units.

5- Calculate the standard cell potential at 25 ∘ C for the reactionX(s)+2Y + (aq)→X 2+ (aq)+2Y(s) where ΔH ∘ = -633kJ and ΔS ∘ = -391J/K.Express your answer to three significant figures and include the appropriate units.

6- Consider the reaction Mg(s)+Fe 2+ (aq)→Mg 2+ (aq)+Fe(s) at 67 ∘ C, where [Fe 2+ ]= 3.80M and [Mg 2+ ]= 0.310M.

What is the value for the reaction quotient, Q , for the cell? Express your answer numerically.

What is the value for the temperature, T , in kelvins?Express your answer to three significant figures and include the appropriate units.

What is the value for n ?Express your answer as an integer and include the appropriate units (i.e. enter mol for moles).

Calculate the standard cell potential for Mg(s)+Fe 2+ (aq)→Mg 2+ (aq)+Fe(s) Express your answer to three significant figures and include the appropriate units.

7- A voltaic cell employs the redox reaction:2Fe 3+ (aq)+3Mg(s)→2Fe(s)+3Mg 2+ (aq) Calculate the cell potential at 25 ∘ C under each set of conditions:

[Fe 3+ ]= 2.2×10−3M ; [Mg 2+ ]= 2.60M Express your answer using two decimal places.
[Fe 3+ ]= 2.60M ; [Mg 2+ ]=2.2×10−3M Express your answer using two decimal places.

8- A Cu/Cu 2+ concentration cell has a voltage of 0.22V at 25 ∘ C . The concentration of Cu 2+ in one of the half-cells is 1.4×10−3M.What is the concentration of Cu 2+ in the other half-cell? Express your answer using two significant figures.

9- Galvanized nails are iron nails that have been plated with zinc to prevent rusting. The relevant reaction is Zn 2+ (aq)+2e − →Zn(s) For a large batch of nails, a manufacturer needs to plate a total zinc mass of 3.30kg on the surface to get adequate coverage. How many moles of zinc are in 3.30kg of zinc? Express your answer to three significant figures and include the appropriate units.

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Electrochemistry Part III

1- Balance each redox reaction occurring in acidic aqueous solution. Express your answer as a chemical equation. Identify all of the phases in your answer.

Ni(s)+Cd 2+ (aq)→Ni 2+ (aq)+Cd(s)
Ni(s)+Cd 2+ (aq)→Ni 2+ (aq)+Cd(s)
3MnO 4 − (aq)+5Al(s) + 24H+(aq)→3Mn 2+ (aq)+5Al 3+ (aq) + 12H2O (aq).

2- Balance each redox reaction occurring in basic aqueous solution.

2MnO − 4 (aq)+Br − (aq) +H2O→2MnO 2 (s)+BrO − 3 (aq) + 2OH-
4Ag(s)+8CN − (aq)+O 2 (g) +2H2O→4Ag(CN) − 2 (aq) +4OH-
O − 2 (aq)+Al(s)→NH 3 (g)+AlO − 2 (aq) (provide double check this equation since the left since the left side has no N.)

3- Calculate the standard cell potential (E ∘ ) for the reaction X(s)+Y + (aq)→X + (aq)+Y(s) if K = 5.82×10−3.Express your answer to three significant figures and include the ...

#### Solution Summary

The solution assists in solving the electrochemistry and balancing redox equations.

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## Electrochemistry and Redox/half reactions

Balance the following redox equations by the ion-electron method:
1) H2O2 + Fe2+ ---> Fe3+ + H2O (in acidic solution)
CN- + MnO4- ---> CNO- + MnO2 (in basic solution)

2) Calculate the standard emf of a cell that uses the Mg/Mg2+ and Cu/Cu2+ half cell reactions at 25 deg C. What is the equation for the cell reaction that occurs under standard-state conditions?

3) If 2.50 g of CuSO4 are dissolved in 9.0 x 102 mL of 0.30 M NH3, what are the concentrations of Cu2+, Cu(NH3)2+4, and NH3 at equilibrium? (I am so lost on this one!)

4) In the complex ion [Fe(CN)6]4-, the oxidation number of Fe is_____??

5) Consider an electrochemical cell constructed from the following half cells, linked by an external circuit and by a KCl salt bridge:

an Al(s) electrode in 1.0 M Al(NO3)3 solution
a Pb(s) electrode in 1.0 M Pb(NO3)2 solution

What is the balanced overall (net) cell reaction?
a. Pb(s) + Al3+(aq) Pb2+(aq) + Al(s)
b. 3Pb(s) + 2Al3+(aq) 3Pb2+(aq) + 2Al(s)
c. 3Pb2+(aq) + 2Al(s) 3Pb(s) + 2Al3+(aq)
d. Pb2+(aq) + Al(s) Pb(s) + Al3+(aq)

6) Calculate the cell emf for the following reaction:

2Ag+(0.010 M) + H2(1 atm) 2Ag(s) + 2H+ (pH = 10.0)

7) Calculate the value of Eocell for the following reaction:

2Au(s) + 3Ca2+(aq) 2Au3+(aq) + 3Ca(s)
I don't know if seeing how I am attempting to do the problems will help in giving me some guidance, but I included the solution I reached with this problem. My question is-does a negative free energy mean I need to use a positive figure in my calculation? I am not good at algebra (you could probably tell), but I suspect this to be the case. Not mentioned in the text-I know I am supposed to know this. Your detailed explanations are a big help!
8) In the Mond process for the purification of nickel, CO is passed over the metallic nickel to give Ni(CO)4:
Ni(s) + 4CO(g) &#61663;&#61664; Ni(CO)4(g)
Given that the standard free energies of formation of CO(g) and Ni(CO)4(g) are -137.3 kJ/mol and -587.4 kJ/mol, respectively, calculate the equilibrium constant of the reaction at 80 Degrees C. (Assume Gfo to be independent of temperature)

Here is my attempt:
Gibbs free energy = standard free energy of formation of products - standard free energy of formation of reactants

Gibbs free energy = Gf(Ni(CO)4) - Gf(Ni(s)) -4Gf(CO)

Gibbs free energy = -587.4 - 0 + (4 x 137.3)

Gibbs free energy = -587. 4 + 549.2 = -38.2 kJ/mol

K = e (-Gibbs free energy/RT)

K = e (-38200 J/mol/(8.314 J/K.mol x 353K))

K = e (-13.016033)
= 2.2 x 10 -6 (if positive number used, would be K = e (13.016033) = 449,563.7241

9) Which is the systematic name for the compound represented below?

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