First law of electrolysis: it state that mass of the substance liberated or deposited at electrode in electrolysis process is proportional to the quantity of electric charge passed through the solution(electrolyte or system).
If m be the mass of the substance deposit at cathode when Q amount of charge is pass on solution.
Then m α Q
Or, m=ZQ where Z is called proportionality constant called electrochemical equivalent of the given substance.
Or, m=ZIt where Q=It
Experimental verification of the first law of electrolysis
When the current is constant
Cathode plate was placed inside the voltmeter after cleaning, washing ,drying and weighting then the current is passed on the solution for a particular time suppose t1 as shown in figure and the cathode plat was again weighted after passing the current let the deposited copper at cathode is m1.
Again the same current is passing for other particular time t2 and the deposited mass is m2.
Then we have
= or, m α t ………………..i)
For the constant time: let m1 and m2 be the mass deposit at the cathode plate at for the same in travel of time by passing varying current I1 and I2 in the above arrangement then we have
=or, m α t……………..ii)
From eq. 1 and 2 we have, m α It
Or, m α It
Or, m α Q where (Q=It)…………....iii)
Here eq. 3 is faraday’s first law of electrolysis and say that ion deposit at cathode is directly proportional to amount of the charge passes through solution.
Very very important:
Second law of electrolysis:
It state when same amount of electric charge passes through different solution (electrolyte or system) then the mass of the substance deposit or liberated at electrode is directly proportional to their chemical equivalents.
If m1, m2, m3, m4, m5 be the masses liberated in different voltmeter when same current is passes through them and E1, E2, E3, E4, E5 be chemical equivalent respectively. Then we have
== or, = a constant
Experimental verification of faraday second law of electrolysis
For the experimental verification of second law of faraday’s let us consider silver voltmeter, copper voltmeter and water voltmeter are connected in series as given below.
Figure
If we pass same current for same in travel of time then the mass liberated or deposited on respective cathode is m1, m2, m3 .i.e. Mass deposit at silver cathode is m1, mass deposit at copper electrode is m2 and mass deposit at hydrogen electrode is m3.then,
=
Where, E1, E2, E3, be chemical equivalent of silver, copper and hydrogen respectively.
Chemical equivalent of a substance:
It is the ratio of atomic mass and valency of a substance.
So, Chemical equivalent =
Electrochemical equivalent
We have, m = zq.
So, z =
If q = 1 colomb, z = m.
Hence, the electrochemical equivalent of a substance is defined as the amount of mass of the substance liberated or deposited in electrolysis when a charge of 1 colomb is passed through the electrolyte of substance.
In SI, m is expressed in kg and q is expressed in colomb(c). Hence, the unit of Z is kgC-1. However, more conviently, the ECE of a substance is expressed in gram per colomb (gC-1).
The quantity of charge required to deposit one gram equivalent (i.e. one chemical equivalent expressed in gram) of any substance is known as faraday. Its value is 96.500 Cml-1.
Primary cell:
A cell in which the chemical reactions are not reversible is called primary cell. When the cell delivers a current, its active material is used up. When the active material is finished, the cell stops delivering current. Now, for the cell to deliver current again, new electrolyte is to be replaced or a new cell is to be used. Due to this reason, the primary cells are expensive. Voltaic cell, dry cell, Lalancehe cell and Daniel cell are example of primary cell.
Secondary cell:
A cell in which chemical reactions are reversible is called secondary cell. When the cell delivers current, it plates change their chemical composition, the cell plates change all of their chemical composition, the cell is exhausted. The secondary cells are also called storage cells as accumulators. The most common secondary cells are (i) Lead Acid accumulators and (ii) Alkali accumulator.
Difference between primary and secondary cell:
Primary cell.
|
Secondary cell.
|
(i) Chemical reaction is irreversible .
|
Chemical reactions are reversible.
|
(ii) These cells cannot be recharged
|
These cells can be recharged.
|
(iii) These cells have high internal resistance.
|
These cells have low internal resistance.
|
(iv) High current are not obtained
|
High current can be obtained.
|
Different between Ionic and Electronic conduction:
Ionic conduction
|
Electronic conduction
|
|
a. the electronic conduction is possible inside the metallic conductor as well as semiconductor.
|
The number density (n) of ions in an electrolyte is very small as compared to that of free electrons in a metallic conductor.
|
The number density (n) of free electrons in a metallic conductor is higher then that of ions in an electrolyte
|
The drift velocity of ions in ionic conduction is smaller than small of electrons in electronic for a given electric field.
|
The drift velocity of electron in electronic for a given electric field is greater then that of the ionic conductance.
|
The resistance offered by the solution to ions in ionic conduction is much more than that offered by the metal to the drifting free electrons in electronic conduction.
|
The resistance offered by the metal to the drifting free electrons in electric conductionis less than thatof the ionic conduction.
|
Electrochemical equivalent:
The electrochemical equivalent of a substance is defined as the amount of mass of the substance liberated or deposited in electrolysis when a charge of 1C is passed through the electrolyte of the substance.
The relation between chemical equivalent & electrochemical equivalent:-
Let Q amount of charge is passed through two electrolytes whose chemical equivalents are E1 and E2 and electrochemical equivalent are z1& z2 respectively. If m1& m2 are the masses of the ions liberated or deposited in voltmeter respectively, then we have:
M1 =z1Q & M2= z2Q
Faraday’s constant:
Faraday’s constant is defined as the amount of charge requires depositing or liberating one mole of monovalent substance during electrolysis. The approximation value of the faraday’s constant is equal to 96500C/mole.
It is given by F= (EQ)/m
Where F= faraday’s constant
E=chemical equivalent of the substance
Q=charge and m=mass of deposit or liberate.
so finally,
Electrolysis:
The process of decomposition of an electrolyte into its constituent ions by the passage of electric current is called electrolysis.
If you find any mistakes the comment in the comment section below.
I don't own any of the content, these has been sent me to my dear students.
Thank you!!!!!!
0 Comments