LinkedIn Insight Engineering Chemistry -Engineering-VTU-July- 2018-Solution - Grad Plus

Engineering Chemistry -Engineering-VTU-July- 2018-Solution

Visvesvaraya Technological University

B.E. First Semester All Branches (C.B.C.S.) 

Engineering Chemistry

TIME: 3HOURS                                                                                                                                                      MAXIMUM MARKS-80

Note-Answer FIVE full questions, choosing one full question from each module.

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Q1.a) What are reference electrodes? Describe the construction and working of Calomel electrode mention the use.  [7M]

ANS:-Reference electrode:-

a)The electrode of standard potential, with reference to the potential of another electrode is called reference electrode.

b)The most commonly used reference electrode is the Hydrogen electrode. The potential of all other electrodes are measured with reference to the hydrogen electrode. Therefore, it is called as reference electrode.

c)Other more Reference electrodes available which are standardized using a standard electrode and then used as reference electrodes for measuring the potential difference of other electrodes. So, these electrodes are called as secondary reference electrodes.

Calomel Electrode.

Calomel Electrode is a secondary reference electrode. Calomel is also known as mercurous chloride and it is soluble in water.

Construction:

i)It consists of a thin layer of pure mercury at the lowest portion of the container. And on that paste of Hg+Hg2Cl2  is placed.

ii)The remaining part of the cell is filled with a solution of a normal or saturated solution of KCl.

iii)A wire made of platinum is dipped into the layer of mercury is used for making electrical contact. The side-tube is used for making electrical contact with the help of a salt bridge.

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Working:

i)The electrode is represented as,

Pt,Hg(l) ,Hg2Cl2(S)|KCl (xM) saturated with Hg2Cl2

ii)The electrode is of reversible type, if the reduction is occurring at this electrode, the reaction is as follows,

Hg2Cl2(S)⇔Hg2++2Cl

Hg2+2  +2e⇔2Hg


Hg2Cl2(S)+2e⇔2Hg+2Cl

Nernst Equation for the calomel electrode is,

\[ E_{Hg/Hg_2Cl_2}=E_{Hg/Hg_2cl_2}^0-\frac{2.303RT}{nF}\;\log\lbrack Cl^-\rbrack^2 \]

The potential of this electrode depends on the concentration of KCl. Calomel electrode with saturated KCl and 1M KCl have value of 0.2412 V and 0.28V.

Uses:-

1)Easy to construct and easy to transport.

2)Used in corrosion studies

3)Use to determine the potential of other electrodes.

4)Commonly used as a reference electrode.

 

b)Define battery. Explain the construction, working, and uses of Ni-metal Hydride battery. [7M]

ANS:-Battery:-A device consisting of a number of galvanic cells that can generate electric power and can act as a portable source of electrical energy. It is a compact device. It stores chemical energy in the form of active materials and converts it into electrical energy through redox reactions.

Nickel-metal hydride battery:

Usually these batteries are alklaine and rechargeable.

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Construction:-

i)The anode used is made up of metal hydride like MH and MH2. Active hydrogen storage alloy like LaNi5 are put on a very thin, highly porous nickel sheet.

ii)Cathode,is made of NiO(OH) is also put on thin and highly porous nickel sheet.

iii)Electrolyte used is aqueous potassium hydroxide.

iv)A thin layer of polypropylene is poured into the separator.

v)All the components are in glass container.

Working:-

Cell Representation:

MH2 |KOH(5M)| Ni(OH)2,NiO(OH)

Reactions:

At anode: MH2+2OH→M+2H2O+2e

At cathode: NiO(OH)+H2O+e→Ni(OH)2+OHX 2

Net Reaction: MH2+2NiO(OH)→M+2Ni(OH)2

EMF of the battery is 1.3V.

Advantages:

1)High capacity

2)Zero maintenance required

3)Long life

4)If there charge there is long shelf life.

5)Less environmental problem.

6)Recharging capability is rapid.

Applications:

There are various use of Nickel-metal hydride batteries. These batteries are used in computers, cellular phones, and other portable and consumer electronics applications where high specific energy is required.

c)What are fuel cells? Explain the construction and working of methanol oxygen fuel cells.  [6M]

ANS:-Fuel Cell:-Electrochemical cells are usually fuel cells. It consists of two electrodes and an electrolyte which help to convert the chemical energy of the chemical reaction between fuel and oxidant which converts directly into electrical energy.

The ordinary combustion process of fuel is

Fuel+Oxygen→ Combustion products+Heat

The process of the fuel cell is,

Fuel+ Oxygen→Oxidation products+Electricity

The process is the same as the electricity generator set, which helps to convert the chemical energy of diesel and air into electricity.

The conventional process to produce electrical energy is as follows:-

Chemical energy→Heat→Mechanical energy→Electrical energy

Methanol-Oxygen Fuel cell:-

Construction:-

  • These cells can be used either in alkaline or acidic mediums.
  • Methanol is used as fuel which has low carbon content and has easily oxidizable-OH group present in it.
  •  It consist of anodic and cathodic compartments. It contains a platinum electrode.
  • The electrolyte used is H2SO4 and it is passed through cathodic compartments. Oxygen is passed through the cathodic compartment.
  • To prevent the diffusion of methanol into cathode A membrane is provided.
  • The cells has emf of 1.2V

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Working-

Cell Reactions:-

At anode:-     CH3OH+H20→CO2+6H++6e

At Cathode:-  3/2O2+6H++6e→3H2O

Net cell reaction CH3OH+3/2O2→CO2+2H2O

Advantages:-1)Methanol has a low content of carbon

2)It is highly soluble in water.

3)The OH group is highly soluble in water.

Applications:- Used in equipment such as battery chargers and autonomous power for test and training equipment which is mostly used in military equipment.

Q2.a)Define single electrode potential? Derive Nernst equation for the single electrode. [7M] 

ANS:-Single Electrode potential:-An electrochemical cell consists of two half-cells. With an open circuit, the metal electrode in each half-cell transfers its ions into a solution. Thus an individual electrode develops a potential with respect to the solution. The potential of a single electrode in a half-cell is called the Single electrode potential.

Nernst’s equation is used for finding single electrode potential and EMF of a given cell.

Taking into consideration a redox reaction.

Mn++ne⇔M

The change in free energy for the above reaction is as follows:

ΔG=-nFE  ……………………………… (a)

Under standard conditions, when the concentration is unity, the standard free energy change is as follows:

ΔG0=-nFE0  ………………………………..(b)

The equilibrium constant K is associated with the change in free energy change by the VantHoff equation,

ΔG=ΔG0+RT ln K ……………………….(c)

Where K=[M]/[Mn+] put the value ok K in equation (c)

ΔG=ΔG0+RT ln [M]/[Mn+]

ΔG=ΔG0+RT ln [M]-RT ln[Mn+]……………(d)

Put the values of ‘G’ and ‘G0‘ from equations (b) and (c) in equation (d).

-nFE=-nFE0 +RT ln[M] -RT ln[Mn+]

Divide both sides by -nF

\frac{-nFE}{-nF}=\frac{-nFE^0}{-nF}+\frac{RT\;ln\lbrack M\rbrack}{-nF}-\frac{RT\;ln\mathit\;\lbrack\mathrm M^{\mathrm n+}\rbrack}{-nF}

Under standard conditions,M=1 hence above equation becomes,

E=E^0+\frac{RT\mathit\;ln\;\lbrack M^{n+}\rbrack}{nF}

Put R=8.314 JK-1 mol-1

F=96500 C mol-1 ,T=250C

Now, covert ln to log base 10 the above equation becomes,

And the equation becomes,

E=E^0+\frac{0.0591}n\log_{10}\;\;\lbrack M^{n+}\rbrack\;

 

b)What are concentration cells? The cell potential of Ag concentration cell,\frac{Ag_{(s)}}{AgNO_3}(0.001M)(AgNO_3(XM)/Ag_{(s)}\; is 0.0659V at 250C .Write the cell reactions and calculate the value of X . [7M]

ANS:-Given:- C1=0.001M ,C2=xM ,n=1

Ecell=0.0659 V

\begin{array}{l}E_{cell}=\frac{0.0591}n\;\log\frac{C_2}{C_1}\\\\0.0659=\frac{0.0591}n\log\frac x{0.001}\\\\x=0.0130\;M\end{array}

Cell Reaction:-

At anode     Ag→Ag++ne

At cathode  Ag++ne→Ag

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Ag+↔Ag+

 

c)Write a note on i)Capacity ii)Cycle life iii)Voltage [6M]

 

 

Q3.a)Define corrosion .Explain the electrothermal theory of corrosion by taking iron as an example.  [7M]

b)What is anodizing? Explain anodizing of aluminum,mention use. [7M]

c)Define electroless plating. What are the difference between electroplating and electroless plating? [6M]

 

OR

Q4.a)What is differential aeration corrosion? Explain pitting corrosion with anode and cathode reactions. [7M]

b)Define metal finishing? Explain electroplating of Nickel by Watt’s bath, mention the uses. [7M]

c)What is cathodic protection? Explain the sacrificial anode method and impressed current method. [6M]

 

Q5.a)Define GCV and NCV? How the calorific value of a solid/liquid fuel is determined using Bomb Calorimeter. [7M]

b)Define octane and cetane number? What is the objective of reforming of petrol and discuss the various methods of reforming? [5M]

c)What are solar cells? Describe the method of purification of silicon by zone refining. [6M]

 

Q6.a)A coal sample containing 92% C,7% H2, and 3% ash is subjected to combustion in a bomb calorimeter .Calculate the Gross and net calorific values. Given that mass of coal, sample is 0.85×10-3 Kg, mass of water in copper calorimeter is 2 Kg, water Equivalent of calorimeter is 0.75kg, rise in temperature of water is 2.50C ,latent heat of steam is 2454kJ/kg and specific heat of water is 4.187 kJ/kg/0C. [7M]

b)Describe the production of solar-grade Si by the union carbide process. [6M]

c)Explain the construction and working of a PV cell. [6M]

 

Q7.a)What are polymers? Illustrate the mechanism of addition polymerization by taking vinyl chloride as an example. [7M]

b)Describe the manufacture of i)PMMA ii)Kevlar Mention the use. [7M]

c)Define addition and condensation polymerization process with one example each. [6M]

 

Q8.a)Define glass transition temperature. Explain any three factors affecting Tg. [7M]

b)What are elastomers? Give the synthesis and application of i)Silicon rubber ii)Epoxy resin. [7M]

c)A polymer sample containing 50,100 and 150 molecules having molar mass 2000 g/mol 2500 g/ml and 3000 g/mol respectively. Calculate the number average and weight average molecular mass of the polymer. [6M]

 

Q9.a)What is boiler feedwater ? Explain the difference between scale and sludge formation in the boiler.   [7M]

b)What is desalination? Explain desalination of seawater by electrodialysis. [7M]

c)What are nanomaterials? Explain the synthesis of nanomaterial by sol-gel method. [6M]

 

Q10.a)Define COD and BOD. In the COD test 25.5cm3 and 12.5cm3 of N FAS solution are required for blank and sample titration respectively. The volume of the test sample used is 26cm3. Calculate the COD of the sample solution.  [8M]

b)Describe the synthesis of nanomaterials by chemical vapor condensation process.  [6M]

c)Write note on CNT and dendrimers.  [5M]

 

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