I'm about to have a chemistry exam within some days, and I have some doubts about these two exercises.
The first is about electrochemistry:
I'd also like to know how the redox would be.
The second one is about electrolysis:
This is what I do:
REDOX
2H2O + 2e- ---> H2 + 2OH
2H2O ---> O2 + 4H+ + 4e-
so we have z = 2 for H2 and z = 4 for O2. Now the moles:
n(H2) = i * t / z * F = 0.559 mol
n(O2) = i * t / z * F = 0.279 mol
Since both are gas, let's use the perfect gas equation, pv = nRT
V(H2) = nRT / p = 10 l
V(O2) = nRT / p = 4.98 l
I assume it's ok until this, but that 10% of water (or sulfuric acid, since the original text is not clear) bugs me. Do I have to calculate 90% of the volume or it's ok as it is right now?
The first is about electrochemistry:
Quote:Calculate electromotive force according to this:Now, I know all the stuff about Nernst equations etc, the right part bugs me though. What do I have exactly to do with those three concentrations? (MnO4-, Mn2+, H3O+).
Pt (O2 = 1 atm) / [OH-] = 10^-3 M // [MnO4-] = 10^-2; [Mn2+] = 10^-3 M ; [H3O+] = 10^-2 / Pt
E°O2/OH- = 0.41 V; E°MnO4-/Mn++ = 1.51 V.
I'd also like to know how the redox would be.
The second one is about electrolysis:
Quote:Due to a reaction of an aqueos solution of sulfuric acid 10%, we get H2 on the cathode and O2 on the anode. According to these information, calculate H2 and O2 volumes.
P= 1010 torr (1.32 atm)
T = 15°C (284 K)
t = 2 hours (7200 s)
i = 15 amp
This is what I do:
REDOX
2H2O + 2e- ---> H2 + 2OH
2H2O ---> O2 + 4H+ + 4e-
so we have z = 2 for H2 and z = 4 for O2. Now the moles:
n(H2) = i * t / z * F = 0.559 mol
n(O2) = i * t / z * F = 0.279 mol
Since both are gas, let's use the perfect gas equation, pv = nRT
V(H2) = nRT / p = 10 l
V(O2) = nRT / p = 4.98 l
I assume it's ok until this, but that 10% of water (or sulfuric acid, since the original text is not clear) bugs me. Do I have to calculate 90% of the volume or it's ok as it is right now?