Question

What are concentration cells? Give examples
A) Galvanic cell composed of two same half cells.
B) A cell which has two electrodes which are not identical but placed in the same solution.
C) A cell in which potential is created via exchange of electrons
D) All of the above

Answer 1

Hint: Looking at all options carefully before answering. Nernst equation is used to calculate the reduction potential of a cell. Concentration cell consists of two half cells which have different concentrations but the same composition. Using Nernst's equation we can calculate the potential that is caused by the concentration cell.

Complete step by step answer:
Nernst equation can be represented as:
$$E_{cell}=\left({E^o}_{cell}-{\displaystyle \frac{0.059}{2}}\right)\times logQ$$
$$E_{cell}$$= Reduction potential
$${E^o}_{cell}$$= Standard potential
$$Q$$= Reaction quotient
$${\displaystyle \frac{0.059}{2}}$$ =Constant after solving the equation.
When the electrons are transferred between two half cells, the one having high concentration gets diluted to lower concentration and the other having lower concentration will increase its concentration, due to which there comes a stage when both concentrations are equal to each other and that state is termed as equilibrium state and potential difference between the two half cells is created.
Concentration cells are of two types:
- Electrode Concentration cell
- Electrolyte Concentration cell
We can understand an Electrode concentration cell as two hydrogen electrodes that have different pressures which does not make them identical but placed in the same solution (which has hydrogen ions).
$$H_{2(P1)}/Solutionof{H}^{+}ions/H_{2(P2});Pt$$
Where P represents Pressure
In an electrolyte concentration cell, both the electrodes are of the same metal and placed in solution of the same ion. This type of concentration cell can be represented as:
$$Zn;Z{n^{2+}}_{a1}//Z{n^{2+}}_{a2};Zn$$
Where a represents activity
Option A) this option can be correct as the concentration cell is the galvanic cell that is made up of two half cells but we must look at all the options given.
Option B) This option can be correct as this type of cell is an electrode concentration cell as discussed above.
Option C) this option can be correct as in this type of cell potential is created when electrons are exchanged from different concentrations.
Option D) this is a correct option as all of the above options are right.

Hence, the correct answer is, ‘Option D’

Note: Electrode and electrolyte cells are the type of concentration cells. We also remember that the electrodes are used to measure the conductivity of the cell and also used in different types of battery electrolysis processes.