Redox reactions

[anteater85]

Can someone help me with this:
Given that the E0 for Au+3/AU is 1.5 V and the E0 for Li+/Li is -3.05 V. what is Ecell for the reaction: Au3+ +3 Li-->Au + 3 Li

if [Li+]= 10 M and [Au3+] = 0.01 M

Thank you

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[nze82]

Can someone help me with this:
Given that the E0 for Au+3/AU is 1.5 V and the E0 for Li+/Li is -3.05 V. what is Ecell for the reaction: Au3+ +3 Li-->Au + 3 Li

if [Li+]= 10 M and [Au3+] = 0.01 M

Thank you

A) Write the two half reactions:

Au3+ + 3e- --> Au, Eo = +1.5V

Li+ + 1e- --> Li, Eo = -3.05

Which half reaction has a higher reduction potential? The first one.
So, the 2nd reaction must be the one that is oxidized. So, let's flip the reaction and the sign of Eo for this reaction:

Au3+ + 3e- --> Au, Eo = +1.5V

Li --> Li+ + 1e-, Eo = +3.05

B) Multiply the two reaction with proper coefficients, so that you can cancel out the electrons (DO NOT multiply the reduction potential by these coefficients):


1(Au3+ + 3e- --> Au), Eo = +1.5V

3(Li --> Li+ + 1e-), Eo = +3.05
**************************
Au3+ + 3Li --> Au + 3Li+, Eo = 1.5 + 3.05 = 4.55V

C) Use the Nernst equation:

n = 3 (# of electrons)
Q = [Li+]^3/[Au3+]^1

E = Eo - (0.0591/n)logQ

= 4.55 - (0.0591/3)log(10^3/0.01) = +4.45V

 

[anteater85]

A) Write the two half reactions:

Au3+ + 3e- --> Au, Eo = +1.5V

Li+ + 1e- --> Li, Eo = -3.05

Which half reaction has a higher reduction potential? The first one.
So, the 2nd reaction must be the one that is oxidized. So, let's flip the reaction and the sign of Eo for this reaction:

Au3+ + 3e- --> Au, Eo = +1.5V

Li --> Li+ + 1e-, Eo = +3.05

B) Multiply the two reaction with proper coefficients, so that you can cancel out the electrons (DO NOT multiply the reduction potential by these coefficients):


1(Au3+ + 3e- --> Au), Eo = +1.5V

3(Li --> Li+ + 1e-), Eo = +3.05
**************************
Au3+ + 3Li --> Au + 3Li+, Eo = 1.5 + 3.05 = 4.55V

THank you

 

[nze82]

THank you

Just as a side note:
You can always check your work by looking at the final answer. E should NOT differ drastically from Eo (4.55 vs. 4.45).