[Astrokel]

hey all,

i've attached two documents, and what confused me is (b). Nernst equation is not in the syllabus so i don't know anything about it.

in bi) they asked to calculate the standard electrode potential, isn't standard means the one found in data booklet?

As for bii), do i have to calculate E_cell to work out the K_c value?

thank you..

[Astrokel]

oops i forgot to attach. is it better to upload in .pdf?

[Borek]

Nernst equation is not in the syllabus so i don't know anything about it.

It is given in the from required, so don't worry too much.

they asked to calculate the standard electrode potential, isn't standard means the one found in data booklet?

Lousy wording IMHO. You are asked to calculate so called formal potential. Just find the concentration using Faraday's law.

do i have to calculate E_cell to work out the K_c value?

What does it mean "cell stopped working"?

[Astrokel]

hi would you mind helping me check my work, because i have no solutions.

ai) Fe³⁺ + e^-  ---> Fe²⁺  E = +0.77V
    Ni  -----> Ni²⁺ +2e^-                   E = +0.25V
2Fe³⁺ + Ni ---> Ni²⁺ + 2Fe³⁺  E_cell = +1.02V

aii) Ni electrode grows thinner and increasing green solution of Ni²⁺. The solution in Fe³⁺/Fe²⁺ becomes more yellowish-green.

aiii) Q = It = 2 (10 x 60 x 60) = 72000 C

n_e = Q/F = 72000/96500 = 0.746mol

mass of Nickle electrode  = (0.746/2) x 58.7 = 43.8g

bi) [Ni2+] = (0.746/2) / 1 = 0.373 mol dm^-3

E_Ni²⁺/Ni = 0.25 - 0.0128 ln (1/0.373) = +0.237V


bii)

What does it mean "cell stopped working"?

i think it means the rate of forward reaction equal to the backward? 

[Borek]

I am back from dentist and aching, so I can be wrong.

ai) Fe³⁺ + e^-  ---> Fe²⁺  E = +0.77V
    Ni  -----> Ni²⁺ +2e^-                   E = +0.25V
2Fe³⁺ + Ni ---> Ni²⁺ + 2Fe³⁺  E_cell = +1.02V

Recheck the equation and potential.

mass of Nickle electrode  = (0.746/2) x 58.7 = 43.8g

You mean change in the mass.

[Ni2+] = (0.746/2) / 1 = 0.373 mol dm^-3

What about initial?

What does it mean "cell stopped working"?

i think it means the rate of forward reaction equal to the backward?

That's not wrong, but that's not what I am asking about. In the equilibrium there is no force that can push reaction in neither direction, right? What does it tell about the cell potential?

[Astrokel]

Recheck the equation and potential.

oops its Fe²⁺ at the product side not Fe³⁺. The potential is correct, no?

What about initial?

initial? i thought they want after the cell run for 10 hours?

That's not wrong, but that's not what I am asking about. In the equilibrium there is no force that can push reaction in neither direction, right? What does it tell about the cell potential?

Zero?

thanks!!

[Borek]

The potential is correct, no?

I don't think so, but I am at around 25% of my brainpower atm. This should be difference - higher minus lower.

What about initial?

initial? i thought they want after the cell run for 10 hours?

Yes, but you started with 1M solution and you dissolved your electrode into it.

Zero?

Yes. Think it over, it is important result.

[Astrokel]

Yes, but you started with 1M solution and you dissolved your electrode into it.

[Ni2+] = [(0.746/2) + 1] / 1 

Yes. Think it over, it is important result.

so i can equate the formal cell potential to be zero and solve for Kc part?

sorry but i am really bad at electrochem...thanks again