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4th Week BE 1/4 2013-2014

ELECTRODE POTENTIAL:

The tendency of an element ot loose or gain electrons is called as Electrode Potential. The elements have a tendency to loose electrons is called as Oxidation. And the elements having a tendency to gain electrons is called as Reduction.

Consider a Single Electrode or a Half-Cell in which a metal behaves as electrode is placed in its solutble salt solution which behaves as Electrolyte. Then the following may happen:

Case 1:  M   ---------à Mⁿ⁺   +   ne^-

Case 2:  Mⁿ⁺ +  ne^- --------à  M

The previous one is dominating reaction. Also the flow of electrons may be any one of the following:

• Either electrons may go into solution, or
• electrons may go out, or
• electrons may get accumulated on the electrode.

Of the above, the electrons getting accumulated on the electrode is the one taking place.

Therefore, as a result we have -ve charge on the electrode and +ve charge adjacent to this, which will gives rise an "Electric Double Layer" formed at Electrode-Electrolyte Interface or Junction. At this junction a Potential was developed which is called as "Electrode Potential".


STANDARD ELECTRODE POTENTIAL (E^o):

It is defined as the potential developed at electrode-electrolyte interface, when a metal (electrode) is in contact with its soluble-salt solution (electrolyte) having 1.0M concentration, and it the electrode involves gaseous substance, they are at a pressure 1atm at 25^oC.

SINGLE ELECTRODE POTENTIAL (E):

It is defined as the potential developed at electrode-electrolyte interface, when a metal (electrode) is in contact with its soluble-salt solution (electrolyte) in other than 1.0M concentration, and it the electrode involves gaseous substance, they are at a pressure may or may not be at 25^oC.

It is not possible to measure single electrode potential. Hence it is connected with Standard Hydrogen Electrode (SHE, a Reference Electrode), a known SRP value. 

A Civil Engineer

Civil engineering is one of the most popular and broadest fields of engineering. It is a branch of engineering that deals with the construction and design of highways, dams, buildings, tunnels, bridges, reservoirs and other similar facilities. Civil engineers have a great deal of responsibility in their field. They are directly responsible for the planning and management of construction to take place. Not only do they aid in designing but also take an effective part in estimating, scheduling, obtaining materials, planning, costs, controlling costs and selecting equipment that is to be used.

There are two crucial aspects within this field. You may face difficulty in consulting both a civil engineer and contracting a civil engineer. The key responsibility of a consulting civil engineer is regarding designing of the project while contracting civil engineers deal with the actual construction where they play a significant role in transforming a planned designed layout into real architecture. Moreover, being a civil engineer, there are many further specializations that are an essential part of the sector.

A civil engineer job is engaged in different activities starting from the selection of land to the final construction. Some of the responsibilities and key roles of a civil engineer are as follows:

1. A civil engineer must start from analyzing various areas and factors that are related to designing and construction.
2. Find, investigate and examine the location of the site and verify whether it is appropriate for construction purposes.
3. It’s the job of a civil engineer to work according to a plan with regards to what are the key essentials and what needs to be modified before the construction starts.
4. Review and approve project reports and designs.
5. A civil engineer should develop detailed design layout that covers the requirement of the client.
6. Assess both challenges and potential risks of the planned project.
7. Undertake initiatives for risk management and take appropriate steps for it.
8. A civil engineer’s job also includes putting across construction proposal and site to the specified officials and supervising the tendering process.
9. Ensure that the said rules, regulations and guidelines are followed without any exception.
10. While the project is undergoing, a civil engineer is also responsible for safety measures on site.
11. Analyze and examine different strategies, equations and applications to ensure appropriate procedure application.
12. The civil engineer must also check if all tools and techniques like procedures of chemical testing, land surveying, drafting software and electrical test devices are working properly.
13. Monitor the operations and working of staff on the site.
14. Interact and communicate effectively with other subcontractors, architects and consultants.
15. The civil engineer must think creatively and logically to resolve various issues in the development process.
16. Set a perfect schedule for purchase of equipments and raw materials.
17. Last but not the least, the civil engineer must ensure that the project is completed on time within the planned budget.

It is necessary that both the consultant and field civil engineer maintain constant communication throughout the project. Because both have a high level of responsibility the weight of the entire project, safety, and codes lays upon their shoulders.

3rd Week BE 1/4 2013-2014

Types of Conductometric Titrations:

1. Titration of strong acid (HCl) with strong base (NaOH) :

Initially the conductivity of acid solution is high due to the presence of highly mobile H+ ions. This is represented by point A on the curve.
The conductivity cell is placed in the acid solution taken in the beaker and the alkali in the burette. On gradual addition of NaOH from the burette, highly mobile H+ ions are removed by the added OH- ions to form nearly non-conducting water molecules. 

                                    H+Cl- + Na+OH- _____________> Na+Cl- + H2O

                                                  Acid Base Salt Water(non-conducting)

Hence the conductivity of the solution decreases progressively, till the point B is reached. On further addition of NaOH, the conductivity of the solution will rise along the curve of BC, due to the addition of highly mobile OH- ions to the solution. At the minimum point B, there is no excess of either acid or base and hence, it corresponds to the equivalence point. The conductance at this point B is not zero because of presence of Na+ and Cl- ion in the solution.

2. Titration of a week acid (CH3COOH) and a strong base (NaOH) :

Acetic acid is a weak electrolyte has low conductivity, as represented by A. As NaOH is added, the poorly conducting acid is converted into highly ionized salt, CH3COONa and consequently the conductivity goes up along AB, the deciding factor on this curve is presence of Na+ ions. When the acid is neutralized, further addition of alkali causes a sharp rise in conductance along BC due to presence of highly mobile OH- ions. The intersection of AB and BC represents the equivalence point.

CH3COOH + NaOH _________> CH3COO-Na+ + H2O

3. Titration of mixture of a strong acid and weak acid with as strong base:

In the presence of strong acid, the dissociation of a weak acid is completely suppressed due to common ion effect. Therefore, addition of a base to such a mixture will first result in the neutralization of the strong acid. The weak acid starts reacting only after neutralization of strong acid. In the titration graph, the curve AB represents the neutralization of strong acid, the curve BC represents the neutralization of weak acid and curve CD represents the excess base added.

Point B corresponds to the equivalence point for Strong acid, whereas point C corresponds to total neutralization point, C-D = equivalence point for week acid. 

4. Strong Acid with a Weak Base, e.g. HCl Vs Ammonium hydroxide :

Initially the conductance is high and then it decreases due to the replacement of hydrogen ions. But after the endpoint has been reached the graph becomes almost horizontal, since the excess aqueous ammonia is not appreciably ionized in the presence of ammonium chloride (Fig.)

5. Weak Acid with a Weak Base: 

The nature of curve before the equivalence point is similar to the curve obtained by titrating weak acid against strong base. After the equivalence point, conductance virtually remains same as the weak base which is being added is feebly ionized and, therefore, is not much conducting.

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ELECTROCHEMICAL CELLS:

Chemical changes are always accompanied by energy changes, where the difference appears generally in the form of heat (either evolution or adsorption). The electrical energy is another form of energy. In this reaction system all electron movement takes place through an external electrical conductor and there by tap electrical energy. Conversely, a chemical reaction could be initiated by passing electricity through a reaction system. The chemical and electrical changes are carried in a device called Cell. A cell may be defined as a single arrangement consisting of two electrodes and capable of producing electricity due to chemical reaction and vice versa.

There are two types of cells in which the above electrochemical processes are carried out.

I. An Electrolytic Cell

II. A Galvanic or Voltaic Cell.

Electrolytic cell	Galvanic Cell (Or) Voltaic Cell
An electrolytic cell converts electrical energy into chemical energy.	A Galvanic cell converts chemical energy into electrical energy.
The redox reaction is not spontaneous and electrical energy has to be supplied to initiate the reaction.	Here, the redox reaction is spontaneous and is responsible for the production of electrical energy.
Both the electrodes are placed in a same container in the solution of molten electrolyte.	The two half-cells are set up in different containers, being connected through the salt bridge or porous partition.
Here, the anode is positive and cathode is the negative electrode. The reaction at the anode is oxidation and that at the cathode is reduction.	Here the anode is negative and cathode is the positive electrode. The reaction at the anode is oxidation and that at the cathode is reduction.
The external battery supplies the electrons. They enter through the cathode and come out through the anode.	The electrons are supplied by the species getting oxidized. They move from anode to the cathode in the external circuit.
	(Or Voltaic Cell)

GALVANIC CELL:

Under normal circumstances a redox reaction occurs when the oxidising agent comes in contact with the reducing agent. The electrons are transferred direclty from the reducing agent to the oxidizing agent. In order to tap the energy of the reaction in the form of electrical energy, the reactants must be physically separated so as to prevent direct transfer of electrons. Electrons are then allowed to go from anode to cathode through an external circuit. For this system the individual oxidation and reduction reactions ate the electrodes are caleed Half-Cell reactions.

In order to maintain electrical neutrality of both the compartments the SO4-2 and Zn+2 move across the prous partition. For the movement of each Zn+2 ion from anodic compartment to cathodic compartment there is a concurrent migration of SO4-2 ions from the cathodic compartment to anodic compartment.

The Daniel cell is a typical example of galvanic cell. It consists of a copper rod dipping in a solution of copper sulphate, which is separated with the help of a semi permeable membrane or salt bridge from a solution of Zinc sulphate in which a zinc rod is dipped. The salt bridge prevents the diffusion of the two liquids but allows the passage of ions through it, when the flow of electric current takes place.

Oxidation half cell reaction : Zn ---------à Zn2+ + 2e- (anode: oxidation)

Reduction half cell reaction : Cu2+ + 2e- --------à Cu (cathode: reduction) 

Cell reactions: Zn + Cu2+ -------à Zn2+ + Cu (Redox reaction)

When the circuit is complete the flow of electric current takes place. Here, zinc passes into the solution as Zn2+ liberating two electrons because of its higher electrolytic solution pressure, according to equilibrium reaction. In other words zinc possess lower reduction potential than that of copper.

At anode(-): Zn ---------à Zn2+ + 2e- (Oxidation)

The electrons thus liberated travel along the external circuit to the copper electrode where copper ions Cu2+ gain these electrons and converted to metallic copper.

At cathode(+): Cu2+ + 2e- --------à Cu (Reduction)

The movement of electrons from zinc to copper produces a current in the circuit and the net chemical change described as the cell reaction can be represented as follows.

Zn + Cu2+ -------à Zn2+ + Cu 

The total cell according to the convention is represented as

Zn | ZnSO4 || CuSO4 | Cu

The negative electrode is at the extreme left and the positive electrode on the extreme right. The double vertical between the two liquids signifies the salt bridge or semi permeable membrane separating the two half cells.

2nd Week BE 1/4 2013-2014

APPLICATION OF CONDUCTANCE MEASUREMENTS:

Conductance measurements find extensive application in chemistry and chemical industry for obtainining important information concerning the behavior of electrolytes, for analysis, and for concentration control. 

CONDUCTOMERTRIC TITRATIONS:

Conductance measurements may be employed to determine the end points of various titrations. Consider first the titration of a Strong Acid like HCl with a Strong Base like NaOH. Before base is added, the acid solution has a high content of the highly mobile hydrogen ions which give the solution a high conductance. As alkali is added the hydrogen ions are removed to form water, and their place is taken by the much slower cations of the base. Consequently the conducatance of the solution decreases and keeps on falling with additon of base until the equivalent point is reached. Further additon of alkali introduces now an excess of the fast hydroxyl ions, and these cause the conductance to rise again. When this variation of the conductance of the solution is plotted against the volume of alkali added, the result is curve ABS in Fig.

The descending branch of this curve gives the conductances of a Weak Acid (say Acetic Acid) Vs Strong Base (say NaOH). Since the acid is weak, its conductance is correspondingly low. As base is added, the poorly conducting acid is converted to highly ionized salt, and consequently the conductance goes up along AB. Once the acid is neutralized, addition of excess base causes another sharp increase in conductance, and the curve rises along BC. The equivalnce point is again the intersection of the two straight lines. 

Many titrations can be run conductomertically in water or mixed solvents which would be difficult or impossible with indicatiors, and that the method can be applied to mixtures of weak and strong acids, weak and stong bases, precipitaion, oxidation - reduction, and other types of reactions.

1st Week BE 1/4 2013-2014

CLASS - 1: General Introduction
CLASS - 2: Subject Introduction, Exam Pattern, Assignments etc.
CLASS - 3: Electrolysis

Chemistry is the study of matter, its properties, the changes that it may undergo and how these properties and changes are affected bi its composition. It is important for engineers to have knowledge of chemistry, since they can expect to find problems in fields as diverse as the design and development of new materials, quality control and environmental engineering that are basically chemical in nature. The standing and firmness of a structure is decided by the strength of foundation laid, although it is never expressed to the external world. Similarly the applied and engineering sciences derive strength from basic sciences and their growth is decided by inputs given by basic sciences.

Chemistry is the back bone in designing and understanding the nature of various engineering materials. Many advances in engineering either produce a new chemical demand as in the case of polymers or wait upon chemical developments for their application as in the case of implants and alloys.

Currently, the electronics and computers engineers are waiting for suitable bi polymers and nano molecules for use in super computers. The electrical engineers are in search of proper conducting polymers. The mechanical engineers are on lookout for micro fluids and the Civil engineers are looking for materials that are environment friendly, economical but long lasting. [Ref.: Text book on Eng. Chemistry, CPM, CVA, AN].

The following chapters will be discussed during your 1st Year.

1. Electrochemistry
2. Water Chemistry
3. Thermodynamics
4. Corrosion Science
5. Phase Rule
6. Chemical Fuels
7. Materials Chemistry

UNIT - 1: ELECTROCHEMISTRY


Electrochemistry is the branch of physical chemistry that concerns itself with the interrelation of chemical phenomena and electricity. It deals with the study of the electrical properties of solutions of electrolytes and with the elucidation of the relation between chemical action and electricity in such systems.


Michael Faraday, FRS (22 September 1791 – 25 August 1867) was an English scientist who contributed to the fields of electromagnetism and electrochemistry. His main discoveries include those of electromagnetic induction, diamagnetism and electrolysis.


Although Faraday received little formal education he was one of the most influential scientists in history.[1] It was by his research on the magnetic field around a conductor carrying a direct current that Faraday established the basis for the concept of the electromagnetic field in physics. Faraday also established that magnetism could affect rays of light and that there was an underlying relationship between the two phenomena.[2][3] He similarly discovered the principle of electromagnetic induction, diamagnetism, and the laws of electrolysis. His inventions ofelectromagnetic rotary devices formed the foundation of electric motor technology, and it was largely due to his efforts that electricity became practical for use in technology.


As a chemist, Faraday discovered benzene, investigated the clathrate hydrate of chlorine, invented an early form of the Bunsen burner and the system of oxidation numbers, and popularised terminology such as anode, cathode, electrode, and ion. Faraday ultimately became the first and foremost Fullerian Professor of Chemistry at the Royal Institution of Great Britain, a lifetime position.

Faraday was an excellent experimentalist who conveyed his ideas in clear and simple language; his mathematical abilities, however, did not extend as far as trigonometry or any but the simplest algebra. James Clerk Maxwell took the work of Faraday and others, and summarised it in a set of equations that is accepted as the basis of all modern theories of electromagnetic phenomena. On Faraday's uses of the lines of force, Maxwell wrote that they show Faraday "to have been in reality a mathematician of a very high order – one from whom the mathematicians of the future may derive valuable and fertile methods."[4] The SI unit of capacitance, the farad, is named in his honour. [Ref. http://en.wikipedia.org/wiki/Michael_Faraday]. 

Faraday's Laws Of Electrolysis:

"The mass of a substance involved in reaction at the electrodes is directly proportional to the quantity of electricity passed through the solution". This statement is known as Faraday's First Law of Electrolysis.

The question that immediately arises is: What mass of the substances will this quantity of electricity deposit? 

From a series of experiments Faraday arrived at his Second Law of Electrolysis, defined as, "the masses of different substances are directly proportional to their equivalent weights". Another way of stating this law is that "the same quantity of electricity will produce chemically equivalent quantities of all substances resulting from the process". OR "During electrolysis 96,487 coulombs of electricity will yield one equivalent weight of any substance". [1 Faraday = 96,500 coulombs].

To Watch Video: https://www.youtube.com/watch?v=XdlOVnYTS5s

Electrolysis:

The process of decomposition of an electrolyte by passing electric current through it is called Electrolysis. The process in which it is carried out is called Electrolytic cell. The cell contains aqueous solution of an electrolyte, in which two metallic rods (electrodes) are dipped which is connected to a battery. The electrode in which positive current enters the cell is called ANODE denoted as positive electrode. CATHODE is the negative electrode at which current leaves the cell.

An electrolyte is a substance which in aqueous solution or in molten state liberates ions and allows the passage of electric current to pass through it resulting chemical decomposition. 

Explanation with Electrolysis of Aqueous NaCl Solution:

The Cathode electrode by which electrons from Battery enter the solution. Inturn the electrons leave the solution from the Anode electrode to return to Battery. In solution we have sodium and chloride ions, and also some hydrogen and hydroxyl ions due to the partial ionization of the water.

Now, when the circuit is closed and a current passes through the solution, it is found that chlorine gas excapes at the anode and hydrogen gas at the cathode, while sodium hydrixide forms in the solution immediately adjacent to the cathode. 

Topic 1

A lecture on "Electrode Potential" will be held on 30th September 2013 (Monday) for all BE students of MJCET from 4pm at Room No. 4105.