anteater85

7+ Year Member
Jul 1, 2009
81
1
Status
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
 
May 15, 2009
1,922
3
CA
Status
Dental Student
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


 
Last edited:
OP
A

anteater85

7+ Year Member
Jul 1, 2009
81
1
Status
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
 
May 15, 2009
1,922
3
CA
Status
Dental Student
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).