Electrochemistry is a branch of chemistry that studies chemical reactions which take place in a solution at the interface of an electron conductor (a metal or a semiconductor) and an ionic conductor (the electrolyte), and which involve electron transfer between the electrode and the electrolyte or species in solution.
If a chemical reaction is driven by an external applied voltage, as in electrolysis, or if a voltage is created by a chemical reaction as in a battery, it is an electrochemical reaction. In contrast, chemical reactions where electrons are transferred between molecules are called oxidation/reduction (redox) reactions. In general, electrochemistry deals with situations where oxidation and reduction reactions are separated in space or time, connected by an external electric circuit to understand each process.
Electrochemistry Problems
Introduction to electrochemistry problems
Electro chemistry deals with chemical changes produced by passing electricity.The laws which govern the decomposition of substances on electrodes with passage of current are called Faraday's laws of electrolysis
Problems on Faraday's i Law ( Electrochemistry Problems)
1. Calculate the amount of sodium formed at the cathode by passing 965coulombs of electricity through molten sodium chloride.
Solution: NaCl--------->Na+ +Cl-
At cathode:Na+ + e - ---------->Na
23 grams of sodium is deposited by passing 96500 coulombs of electricity.
------- grams of sodium will be deposited by passing 965 coulombs of electricity.
965 x 23/ 96500 =.23grams
The amount of sodium formed by passing 965 coulombs of electricity is .23grams.
2. Calculate the amount of products formed at the electrodes when 2 Faraday's of electricity is passed through i)molten NaCl ii)aqueous NaCl.
Solution
i) When electricity is passed through sodium chloride the following reactions take place
NaCl--------->Na+ +Cl-
At Cathode:Na+ +e- --------->Na
23grams of sodium is deposited by passing 1Faraday of electricity or 96,500coulombs f electricity.
-------- grams of sodium is deposited by passing 2Faraday's of electricity
23x2=46grams
At Anode:2Cl - --------->Cl2 +2e-
35.5grams(equivalent weight of chlorine)is deposited by passing 1Faraday of electricity.
------grams will be deposited by passing 2Farady's of electricity.
35.5x2=71grams.
ii) when aqueous sodium chloride is subjected to electrolysis the following reactions take place
NaCl--------->Na+ +Cl-
H2O-------->H+ +OH-
At cathode2:H+ +2e- ------------>H2
Na+ do not get discharged at the cathode in the presence of H+ as they require more potential.
1gram of hydrogen gets deposited by passing 1faraday of electricity.
-----grams will be deposited by passing 2faradays of electricity.
1x2=2grams of hydrogen.
At Anode:2Cl - --------->Cl2 +2e- (chloride ions require lesser potential to get discharged compared to hydroxide ions so they get deposited at anode in preference to hydroxide ions)
35.5grams(equivalent weight of chlorine)is deposited by passing 1Faraday of electricity.
------grams will be deposited by passing 2Farady's of electricity.
35.5x2=71grams.
3. Calculate the time required for deposition of 4grams of Magnesium when 365 ampere of current is passed through fused magnesium chloride
solution: MgCl2----------->Mg+2 +2Cl-
cathode: Mg+2 + 2e----------------------> Mg
24 grams of magnesium is deposited by passing 2 Faraday of electricity (2x96,500c)
4 grams is deposited by 25733.3C
C = 365 amperes
Q = C x t
25733.3 = 365 x t
t = 25733.3/365
t = 70.50
Faraday's Second Law (electrochemistry Problems)
QUESTION: An electric current was passed through two voltameter cells containing copper sulphate (using copper electrodes)and the other containing silver nitrate solution (using silver electrodes) .The increase in weight of cathodes in two cases was respectively 0.189gm and 0.648 gm .Calculate the chemical equivalent of copper, taking that of silver as 108.
SOLUTION:
Weight of copper deposited = 0.189 gm
Weight of silver deposited = 0.648 gm
Eq. wt of silver = 108
Eq. wt of copper = ?
According to Faraday's second law
Wt of copper deposited = Eq.wt of copper
Wt . of silver deposited Eq.wt of silver
0.189/0.648 = Eq.wt of copper/108
= 0.189x108/0.648
Eq.wt of copper = 31.5
Electrochemistry Galvanic Cells
Electrochemistry is the study of production of electricity from energy released during spontaneous chemical reactions and the use of electrical energy to bring about non-spontaneous chemical transformations. The subject is of importance both for theoretical and practical considerations.
Introduction to electrochemistry galvanic cells
A large number of metals, sodium hydroxide, chlorine, fluorine and many other chemicals are produced by electrochemical methods. The reactions carried out electrochemically can be energy efficient and less polluting. The transmission of sensory signals through cells to brain and vice versa and communication between cells are known to have electrochemical origin.
Electrochemistry Galvanic Cells
Definition : A galvanic cell is an electrochemical cell that converts the chemical energy of a spontaneous redox reaction into electrical energy. In this device the gibbs energy of the spontaneous redox reaction is converted into electrical energy which may be used for running a motor or other electrical gadgets like heater, fan, geyser, etc.
Daniel cell is also a type of galvanic cell. The redox reaction of a Daniel cell is:
Zn(s) + Cu2+ (aq) âZn2+ (aq) + cu (s)
This cell converts the chemical energy liberated during the redox reaction to electrical energy and has an electrical potential equal to 1.1 V when concentration of Zn2+ and Cu2+ ions is unity. If an external opposite potential is applied and increased slowly, the reaction continues to take place till the opposing voltage reaches the value 1.1 v.
The redox reaction of the cell is a combination of two half reactions whose addition gives the overall cell reaction:
i. Cu2+ + 2e- â Cu (s) (reduction half reaction)
ii. Zn (s) â Zn2+ + 2e- (oxidation half reaction)
These reactions occur in two different portions of the daniell cell. The reduction half reaction occurs on the copper electrode while the oxidation half reaction occurs on the inc electrode. These two portions of the cell are also called half-cells or redox couples. The copper electrode may be called the reduction half cell and the zinc electrode , the oxidation cell.
Summary of Electrochemistry Galvanic Cells
Study of electrochemistry is important for creating new technologies that are ecofriendly.
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