# Calculating Cell Potential Using Nernst Equation for Ag+ Voltaic Cell

• pzona
In summary, this problem is homework from a lab I did yesterday. Normally I would just ask my TA, but since it's homework I can't. I could email him, but I feel like I'll probably get a faster response if I post this here.
pzona
This problem is homework from a lab I did yesterday. Normally I would just ask my TA, but since it's homework I can't. I could email him, but I feel like I'll probably get a faster response if I post this here

## Homework Statement

Use the Nernst equation to determine the cell potential for the cell involving Ag+. This is from a voltaic cell I made using a copper anode and CuSO4 solution and a silver cathode and AgNO3, with a KNO3 solution as a salt bridge. I used a multimeter to calculate the cell potentials for other cells I built (using other metal cathodes and relevant solutions) because their concentrations were 1M, standard conditions. The AgNO3 was 0.1M so I need to use the Nernst equation to calculate cell potential (assuming all other factors, ex. temperature were standard).

Measured potential for the cell: -0.390V
Given oxidation potential for the copper half reaction: +0.34V

## Homework Equations

The Nernst Equation:

E$$_{cell}$$ = E$$^{o}$$$$_{cell}$$ + 0.0592V(mol)/n * log$$_{10}$$Q

Half reaction at the cathode:

Ag+(aq) + e- -> Ag(s), since [Ag+] = 0.1M, Q and n will both be 0.1

## The Attempt at a Solution

Honestly, this comes down to me not understanding what the terms mean. I just started electrochemistry and I haven't been able to find a decent explanation of the terms online.

I'm not sure whether I need to solve for E$$^{o}$$$$_{cell}$$ (I did and got -0.982V) or E$$_{cell}$$ (I got +0.202V). Solving for E$$^{o}$$$$_{cell}$$ makes more sense, given my answer, since I know that silver is a poor reducing agent. It should give a negative answer of fairly high magnitude in relation to the other cells, which it did.

Basically what I'm asking is, E$$^{o}$$$$_{cell}$$ is the quantity I'm looking for...right? Is E$$_{cell}$$ the measured potential for a cell under non-standard conditions? Also, is my answer for E$$^{o}$$$$_{cell}$$ of a reasonable magnitude? Thanks.

EDIT: Looks like my subscripts were messed up somehow. I'm pretty sure you'll be able to figure out what I meant though.

No, you are looking for Ecell of a silver half cell. E0cell you can take from standard potential tables.

Q is 0.1, that's OK, but n is not.

Once you have Ecell of silver half cell, you can calculate E for whole cell.

--
methods

Okay, so for the whole cell, n would be 1.1 mol then? My lab manual says that n is the total amount (in moles) of electrons transferred, so I just add the 0.1 to the 1 from the CuSO4, correct?

No, n is amount of electrons transferred in the half cell reaction. It is always an integer.

--

Ah okay, looking back on it that makes a lot more sense than what I have. Thanks a lot for the help.

## 1. What is the Nernst Equation?

The Nernst Equation is a mathematical equation used to calculate the potential difference (or voltage) across a cell membrane. It takes into account the concentration of ions inside and outside of the cell, as well as the temperature and the charge of the ions.

## 2. What is the significance of the Nernst Equation?

The Nernst Equation is important in understanding the movement of ions across a cell membrane, which is crucial for many biological processes such as nerve impulses and muscle contraction. It also helps to predict the equilibrium potential of an ion, which is the voltage at which there is no net flow of that ion across the membrane.

## 3. How do you solve a Nernst Equation problem?

To solve a Nernst Equation problem, you will need to know the ion concentrations inside and outside of the cell, the temperature, and the charge of the ion. You can then plug these values into the equation and solve for the potential difference (or voltage) across the cell membrane.

## 4. What are some common misconceptions about the Nernst Equation?

One common misconception is that the Nernst Equation only applies to biological systems. In reality, it can be applied to any system with a membrane separating two solutions with different ion concentrations. Another misconception is that the equation only applies to one type of ion at a time, when in fact it can be used to calculate the equilibrium potential for multiple ions simultaneously.

## 5. How does the Nernst Equation relate to the Goldman Equation?

The Nernst Equation is a simplified version of the Goldman Equation, which takes into account not only the concentration but also the permeability of different ions. The Goldman Equation is used when there are multiple types of ions involved and when the membrane is not equally permeable to all ions.

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