# Concentration cell question

• somasimple
In summary, the conversation discusses a concentration cell experiment with two vats containing the same volumes of solutes, and a question about how the Nernst equation is modified in this case. It is clarified that the type of solute does not matter as long as the reacting ion is present on both sides, and the Nernst equation can be modified by calculating the ratio of concentrations. There is a mention of how the cell volumes do not affect the potential, but may play a role in determining the capacity of the battery. It is also noted that the Nernst equation can be extended with certain approaches, and there is no definite upper limit for its use.

#### somasimple

Gold Member
Hi All,
(Just for information and understanding),
If we have a concentration cell experiment like the image uploaded, in a concentration cell, the solutes are supposed to be of the same kind, iI.e. CuCl2 (?).
I suppose it is possible to add to the left vat a m quantity or volume of CuSO4 to increase the RedOx reactions ?
In my experiment, the vats have the same volumes.

How the Nernst equation is modified in that case ?

#### Attachments

• 0300.png
71.6 KB · Views: 384
somasimple said:
in a concentration cell, the solutes are supposed to be of the same kind, iI.e. CuCl2 (?).

No, the only thing that matters is that the reacting ion is present on both sides, counterions can be completely random (that is, as long as they don't interfere).

How the Nernst equation is modified in that case ?

Trivial to derive - just ratio of concentrations.

Bystander
Thanks,
So the reacting ion present on both sides is Cu++.
Trivial to derive - just ratio of concentrations.
For a Chemist for sure!
for example we have 2/3 volume of CuCl2 100 mMol and 1/3 CuSO4 50 mMol at left
and
100% CuCl2 4 mMol at right?

#### Attachments

• nernst_02.PNG
6.1 KB · Views: 316
Thanks for the reply.
Does that means if we do not have access/know the volumes of each concentration, the computation is not possible?

somasimple said:
Does that means if we do not have access/know the volumes of each concentration, the computation is not possible?

Yes, that's what it means.

Thanks,
A last (?) question: What happens when the cell volumes are different, V1 for the left and V2 for the right one ?

Volumes don't matter when it comes to the potential, Nernst equation contains only concentrations.

Amounts of substances play a role when you want to find the capacity of the battery, but that's another story.

Bystander and jim mcnamara
Lower limit - listed in the article you linked to.

Upper limit - depends on what you mean by "equation becomes useless". There are ways of extending its use (they are based on a concept of ionic strength, activity and activity coefficients, listed in the text), and if memory serves me well these extended approaches (like Specific Interaction Theory) work OK to concentrations in the 4-5 M range (which is around a solubility limit for most salts). So the answer is either "works perfectly up to 0.01 M", or "there is no upper limit ".

## 1. What is a concentration cell?

A concentration cell is an electrochemical cell where the anode and cathode solutions have different concentrations of the same electrolyte. This creates a potential difference between the two solutions, which can be measured using a voltmeter.

## 2. How does a concentration cell work?

In a concentration cell, ions will flow from the higher concentration solution to the lower concentration solution in order to balance out the concentrations. This creates a flow of electrons, or an electric current, which can be harnessed for practical use.

## 3. What are some real-world applications of concentration cells?

Concentration cells are commonly used in batteries and fuel cells, where they provide a source of electrical energy. They are also used in various industrial processes, such as metal extraction and wastewater treatment.

## 4. How does temperature affect a concentration cell?

The rate of ion flow and therefore the potential difference in a concentration cell is affected by temperature. An increase in temperature can speed up the rate of ion flow, resulting in a higher potential difference and increased electrical output.

## 5. How do you calculate the potential difference of a concentration cell?

The potential difference of a concentration cell can be calculated using the Nernst equation: Ecell = E°cell - (RT/nF)ln(Q), where E°cell is the standard cell potential, R is the gas constant, T is the temperature in Kelvin, n is the number of electrons transferred, F is Faraday's constant, and Q is the reaction quotient.