Question

a. In Season 2 of Breaking Bad, Jesse and Heisenberg end up stranded in the desert because the battery of the RV is dead. Walter builds a homemade battery to jumpstart the engine. He uses brake pads that contain mercuric oxide (HgO) and galvanized steel which is a source of Zn metal. The electrolyte he uses is KOH. Relevant data can be found in Appendix B. (Below)

i. Write down the relevant half reactions.

ii. What is the overall spontaneous electrochemical reaction?

iii. Calculate the standard potential for this reaction.

iv. If the pH of the electrolyte is 12 and the concentration of zinc ions is 0.01 M what is the cell potential?

b. Silver can be electroplated at the cathode of an electrolysis cell by the half-reaction:

Ag⁺(aq) + e^- ---> Ag(s)

What mass of silver would plate onto the cathode if a current of 6.8 A flowed through the cell for 72 min?

Appendix B: Standard reduction potentials for selected half reactions

Half reaction	E0red (V)
O2(g) + 4H+(aq) + 4 e- ® 2 H2O(l)	1.23
Hg22+(aq) + 2 e- ® 2 Hg(l)	0.85
Ag+(aq) + e- ® Ag(s)	0.80
Fe3+(aq) + e- ® Fe2+(aq)	0.77
HgO(s) + H2O (l) + 2e- ® Hg(s) + 2OH-	0.098
2H+(aq) + 2 e- ® H2(g)	0.00
Ni2+(aq) + 2 e- ® Ni(s)	-0.26
Cd2+(aq) + 2 e- ® Cd(s)	-0.40
Zn2+(aq) + 2e- ® Zn(s)	-0.76
2 H2O(l) + 2 e- ® H2 + 2 OH-(aq)	-0.83
Na+(aq) + e- ® Na(s)	-2.71

I need to know how to do these questions not just the answers, thank you!

Answer 1

a)

i)You are using meric oxide and Zn so the half reactions are (looking into the table):

ii) In order to write the overal reaction you need to identify what is reducing and what is oxidizing, from the statement you know the reactants are HgO and Zn(metal) so, you should write the reactions in the correct order and then sum both reactions

Now you can sum both equations, you should notice (this is not the case) in order to have the overal reaction both reactions should have the same number electrons involve.

Suming both reactions:

iii) The standard potential for the reaction can be calculated with the following equation:

----->E(red) is the potential (from table) of the component that is reducing (HgO) and E(ox) is the potential (from table) of the component oxidizing (Zn)

<----- since you are talking about a spontaneous reaction the potential should be positive

iv) To calculate the cell potential you need to use the nernst equation

where n is the number of electrons involved in the reaction and Q is the reaction quotient (products/reactants)

<-----same as the equilibrium constant, solids and water are considered as 1, thus:

the concetration of OH is calculated from the pH:

<------pH=11 [H]=10^-11

b)

From the current you need to calcualte the amount of charge transfered:

1A=1 C/s

Using the current you need to go back in the reaction:

<----this is from Faraday's constant, which defines the amount of charge transfered by 1 mole of electrons.

You just need to do stoichiometry to solve for the mass of silver.