Chemistry CONCENTRATION CELLS

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CONCENTRATION CELLS

Concentration Cells :

The cells in which EMF arises due to transfer of matter from one half cells to the other because of a difference in the concentration of species involved are known as concentration cells.

If two plates of the same metal are dipped separately into two solutions of the same electrolyte and are connected with a salt bridge, the whole arrangement is found to act as a galvanic cell. In general,

There are two types of concentration cells: See fig.

The cells in which EMF arises due to transfer of matter from one half cells to the other because of a difference in the concentration of species involved are known as concentration cells.

If two plates of the same metal are dipped separately into two solutions of the same electrolyte and are connected with a salt bridge, the whole arrangement is found to act as a galvanic cell. In general,

There are two types of concentration cells: See fig.

Electrode Concentration Cells:

•Two similar electrode at different conc. are dipped in same solution e.g. two hydrogen electrodes at unequal pressure are immersed in same solution of hydrogen ions.In these cells,

•The potential difference is developed between two like electrodes at different concentrations dipped in the same solution of the electrolyte.

•For example, two hydrogen electrodes at different has pressure in the same solution of hydrogen ions constitute a cell of this type.

• `(Pt,H_2` (Pressure `p_1` ))/Anode | `H^(+)` | ( `H_2` (Pressure `p_2` ) `Pt` )/Cathode
`Pt; H_2(p_1) | H^(+)` ions solution `| H_2(p_2); Pt`

See fig.

• `E_(text(cell)) = 0.02955 log (p_i/p_z)`

•In the amalgam cells, two amalgams of the same metal at two different concentrations are interested in the same electrolyte solution.

•Two similar electrode at different conc. are dipped in same solution e.g. two hydrogen electrodes at unequal pressure are immersed in same solution of hydrogen ions.In these cells,

•The potential difference is developed between two like electrodes at different concentrations dipped in the same solution of the electrolyte.

•For example, two hydrogen electrodes at different has pressure in the same solution of hydrogen ions constitute a cell of this type.

• `(Pt,H_2` (Pressure `p_1` ))/Anode | `H^(+)` | ( `H_2` (Pressure `p_2` ) `Pt` )/Cathode
`Pt; H_2(p_1) | H^(+)` ions solution `| H_2(p_2); Pt`

See fig.

• `E_(text(cell)) = 0.02955 log (p_i/p_z)`

•In the amalgam cells, two amalgams of the same metal at two different concentrations are interested in the same electrolyte solution.

Electrolyte- Concentration Cells:

•In these cells, electrodes are identical but these are immersed in solutions of the same electrolyte of different concentrations.

•The source of electrical energy in the cell is the tendency of the electrolyte to diffuse from a solution of higher concentration to that of lower concentration.

•With the expiry of time, the two concentrations tend to become equal. Thus, at the start the emf of the cell is maximum and it gradually falls to zero. Such a cell is represented in the following manner:
( `C_2` is greater than `C_1` ).

• `M|Mn^(+)(C_1)||Mn^(+)(C_2)|M`

•Example: `(Zn|Zn^(2+) (C_1` ))/Anode `|| (Zn^(2+) (C_2 )|Zn)` /Cathode

See fig.

•The emf of the cell is given by the following expression at `25^o C:`

• `E_(text(cell)) = 0.0591/n log (C_1/C_2)`

•The concentration cells are used to determine the solubility of sparingly soluble salts, valency of the cation of the electrolyte and transition point of the two allotropic forms of a metal used as electrodes, etc.

•For every concentration cell `E° = 0`.

•In these cells, electrodes are identical but these are immersed in solutions of the same electrolyte of different concentrations.

•The source of electrical energy in the cell is the tendency of the electrolyte to diffuse from a solution of higher concentration to that of lower concentration.

•With the expiry of time, the two concentrations tend to become equal. Thus, at the start the emf of the cell is maximum and it gradually falls to zero. Such a cell is represented in the following manner:
( `C_2` is greater than `C_1` ).

• `M|Mn^(+)(C_1)||Mn^(+)(C_2)|M`

•Example: `(Zn|Zn^(2+) (C_1` ))/Anode `|| (Zn^(2+) (C_2 )|Zn)` /Cathode

See fig.

•The emf of the cell is given by the following expression at `25^o C:`

• `E_(text(cell)) = 0.0591/n log (C_1/C_2)`

•The concentration cells are used to determine the solubility of sparingly soluble salts, valency of the cation of the electrolyte and transition point of the two allotropic forms of a metal used as electrodes, etc.

•For every concentration cell `E° = 0`.

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