What is an electrolyte concentration cell?
A concentration cell is an electrolytic cell which has two half cells with same types of electrodes but differing in concentration. A concentration cell will dilute more solutions which are concentrated and concentrate more dilute solution thus making a voltage when the cell reaches the equilibrium position. Concentration cell corrosion happens when two or more metal area surface are in contact with different concentration but of same solution.
In the field of chemistry, concentration means amount of a substance per space as defined. Concentration is the ratio of solute in a solution to either to total solution. Concentration usually is expressed in terms of mass per unit volume.
Types: Concentration cells are of two types basically and this is the basic difference between both of them :
- Electrode concentration 2. electrolyte concentration.
The electrode concentration cell are those cell electrodes where both the half cells are made up of the same substances and the electrolyte is the solution of the same substance. However the concentration is different in these cases.
The Electrolyte concentration is where both the half cells are made up of same substances and electrolyte is the solution of the same substance but with different concentration.
Let us consider a battery technology where we take a concentration cell which is basically a limited form of a galvanic cell having two same type half cells having same composition but different concentration.
The methods of concentration cells for unknown solutions are somewhat not known as to the methods for known solution concentration cell. A concentration cell will generate some amount of electricity from the reduction in the thermodynamic free energy of the electrochemical system. There is also a difference in the two half cells and it is reduced. The reaction in the half cells occurs as same but in opposite direction which results in lower and decreasing the higher concentration. The energy is generated from thermal energy that the cell absorbs as the heat while the electricity would flow. There is no temperature gradient.
Metal ion concentration cells: When we have water as the solvent the high concentration of metal ions will exist under some circumstances and a low concentration of metal ions will also exist side by side created by the surfaces. There will be an electric potential between the points. The area of the metal in contact with the lower concentration of metal ions will be in cathodic state and protected and the area of the metal in contact with the higher concentration of metal ions will be thus corroded.
Oxygen concentration cells: The water in contact with the metal surface will dissolve the oxygen, An oxygen cell can develop at any point where the air is not allowed to diffuse uniformly into the solution. This will create a difference in the oxygen concentration between both points. Corrosion will happen in the area of low oxygen concentration which is anodic. Here the EMF that is electromotive force results due to the concentration differences between the reactive constituents. The normal oxygen in artery is about 75 to 100 mm of mercury. Values which are under 60 mm Hg usually mean there is dearth of oxygen and normal pulse oximeter readings would show a range from 95 to 100 percent. Values under 90 percent are considered low supplements.
Active and passive Cells: When a metal is protected against corrosion by an adhesive ( oxide) salt deposits in the surface when in the presence of water the metal will be exposed to some corrosive attach in the areas where the passive film is broken. The electric potential will then develop between the large area of the film and the small area of the exposed active metal. This results in metal pitting.
What is the difference between the electrochemical and electrolytic cell?
Electrochemical cell is also known as Galvanic cell : Here the cell converts chemical energy to electric energy. The redox reaction is spontaneous and responsible for electric energy reaction and production. The half cells are in different containers and connected by a salt bridge or porous film. The electrons are supplied by the species which is being oxidised. Here the anode is negative and the cathode is positive.
Electrolytic cell features as compared to Galvanic Cell: Here the electric energy is being converted to chemical energy. The redox reaction is not spontaneous and electric energy has to be supplied to make the reaction happen. Both the electrodes are kept in same type of container and in a solution of electrolyte. There is an external battery supply which gives away the electrons and they come through the cathode and come out from the anode. The anode here is positive and cathode is negative electrode. The reaction at the anode is oxidation and reduction at the cathode end. This is different from all the basic features from the Galvanic cell.
Refer to learn more from this concept: electrochemistry from class 12 chemistry – find all the questions & answers