QP : Jan-2023 - EC [END SEM]

Que >1(A)

Derive the Nernst equation for oxidation and reduction reaction in detail.

Ans> For the reaction, aA+bB=cC+dD

Where,

A & B = reactants

C & D = products

a& b = number of moles of reactants

c& d = number of moles of product

• When 1 Faraday electricity is passed through the cell, the forward reaction becomes faster.

• According to thermodynamics, the work done in the electrochemical cell is related with decrease in the energy.

-ΔG = nFΔE ………………………….1

ΔG = Free energy change

n= the number of electrons transferred

F= Faraday constant = 96500 coulombs

ΔE= cell potential in volts When the electrochemical cell is in a standard state,

When the electrochemical cell is in a standard state

Where, ΔGo = standard free energy change

ΔEo = standard cell potential

• When a reaction attains equilibrium,

• According to VontHoff’s equation,

Where,

R = gas constant (8.314 J mol-1 K-1)

K = equilibrium constant

But for electrochemical cell

Substitute this value in equation no. 3, we get:

Dividing above equation both the sides by –nF,

Que>1(B)

[I] Discuss the Pitting Corrosion and Stress corrosion in detail.

Ans>

Pitting corrosion Ø The metal surface having pits or cavities undergoes corrosion due to development of separate anodic and cathodic areas. Here pits act as anode with respect to the normal portion. A typical pitting corrosion cell in iron surface is given below. Here corrosion is due to oxygen concentration cell.

Stress corrosion Ø Metallic materials under strain due to mechanical operations like welding, bending, pressing, hammering, etc. During corrosion the stressed portion acts as anode with respect to the normal portion leading to highly localized corrosion. Ø For example, caustic embrittlement, which occurs in mild steel exposed to alkaline solution as stressed areas such as joints and bent portion s at high temperature. Na2CO3 + H2O 2NaOH + CO2 Fe + NaOH Na2FeO3 3Na2FeO3 + 4H2O 6NaOH + Fe3O4 + H2

Que>1(B)

[II] Explain the Voltaic cell with its suitable diagram, reaction and procedure in detail.

Ans> • The galvanic cell uses two different metal electrodes, each in an electrolyte where the positively charge dions are the oxidized form of the electrode metal.

• One electrode will undergo oxidation (the anode) and the other will undergo reduction (the cathode).

• The metal of the anode will oxidize, going from an oxidation state of 0(in the solid form) to a positive oxidation state and become anion.

• At the cathode, the metal ion in solution will accept one or more electrons from the anode and the ion’s oxidation state is reduced to 0. This forms a solid metal that electrodeposits on the cathode.

• The two electrodes must be electrically connected to each other, allowing for a flow of electrons that leave the metal of the anode and flow through this connection to the ions at the surface of the cathode.

• This flow of electrons is an electrical current that can be used to do work, such as turn a motor or power a light.

• In this example, the anode is zinc metal which oxidizes (loses electrons) to form zinc ions in solution, and copper ions accept electrons from the copper metal electrode and the ions deposited the copper cathode as an electro deposit.

• This cell forms a simple battery as it will spontaneously generate a flow of electrical current from the anode to the cathode through the external connection.

• This reaction can be driven in reverse by applying a voltage, resulting in the deposition of zinc metal at the anode and formation of copper ions at the cathode.

• To provide a complete electric circuit, there must also be anionic conduction path between the anode and cathode electrolytes in addition to the electron conduction path.

• The simplest ionic conduction path is to provide a liquid junction

. • To avoid mixing between the two electrolytes, the liquid junction can be provided through a porous plug that allows ion flow while reducing electrolyte mixing.

• To further minimize mixing of the electrolytes, as a bridge can be used which consists of an electrolyte saturated gel in an inverted U-tube.

• As the negatively charged electrons flow in one direction around this circuit, the positively charged metal ions flow in the opposite direction in the electrolyte.

• A galvanic cell whose electrodes are zinc and copper submerged in zinc sulphate and copper sulphate, respectively, is known as a Daniel cell. Half reactions for a Daniel cell are these:

Que>2(A)

Discuss the principle, working mechanism and correction factors of Bom Calorimeter with its diagram in detail.

Ans>

Principle:- A known amount of fuel is burnt in excess of oxygen and the heat liberated is absorbed in a known amount of water. This heat liberated is measured by noting the change in temperature.

Calorific value of the fuel is then calculated by applying the following principle:

Heat liberated by fuel = Heat absorbed by water and the calorimeter.

Construction:-

It consists of the following parts:

Stainless Steel Bomb It consists of a long cylindrical container made up of stainless steel. It has a lid that is made air tight with the help of screws. The lid is provided with two holes for electrodes and has an oxygen inlet valve. A small ring is attached to one of the electrodes. This ring acts as a support for nickel or stainless steel crucible in which the fuel is burnt. Magnesium wire touching the fuel sample extends across the electrodes. The steel bomb is lined inside with platinum to resist corrosive action of HNO3 and H2SO4 vapors formed because of burning of fuel and is designed to withstand high pressure (25–50 atm).
Copper Calorimeter The bomb is placed in a copper calorimeter containing a known amount of water. The calorimeter is provided with an electrical stirrer and a Beckmann thermometer that can read accurate temperature difference of up to 1/100th of a degree.
Air Jacket and Water Jacket The copper calorimeter is surrounded by an air jacket and a water jacket to prevent loss of heat owing to radiation.

Working

· A known amount of fuel (0.5–1 g) is taken in a clean crucible supported over the ring. A fine magnesium wire, touching the fuel sample, is then stretched across the electrodes.

· About 10 mL of distilled water is introduced into the bomb to absorb vapors of sulphuric acid and nitric acid formed during combustion, and the lid of the bomb is tightly screwed.

· The bomb is filled with oxygen at 25 atmospheric pressure and placed in the copper calorimeter containing a known weight of water. The stirrer is started and the initial temperature of water is noted.

· The electrodes are then connected to a 6-volt battery to complete the circuit. The sample burns and heat is liberated. This heat is absorbed by water.

· Maximum temperature shown by the thermometer is recorded. Time taken to cool the water in the calorimeter from maximum temperature to room temperature is also noted. · The gross calorific value of the fuel is calculated as follows.

Que>2(B)

[I]Give the difference between Physical adsorption and Chemical adsorption.

ANS>

Que>2(B)

[II] Define: Adsorption, Negative Catalyst, Promoters & Adsorbate.

Ans>

Adsorption:-

Adsorption is the phenomenon of higher concentration of any molecular species at the surface than in the bulk.

Negative Catalyst:-

When a catalyst reduces the rate of a reaction, it is called a Negative catalyst or Inhibitor. This phenomenon is called Negative catalysis or Inhibition. Negative catalysis is useful to slow down or stop altogether an unwanted reaction

PROMOTERS:-

A substance which, though itself not a catalyst, promotes the activity of a catalyst is called a Promoter.

Que>3(A)

Discuss the classification of thermotropic liquid crystal in detail.

Ans>

->When long chain organic solids are heated, they undergo sharp phase

transition at particular temperature yielding liquid crystal. The phase

transitions involving these intermediate phases are most naturally effected

by the changing temperature and hence , they are called thermotropic liquid

crystal. Example: Ethyl –p-azoxy cinnamate, p-cholesteryl benzoate

->Thermotropic LCs are divided into three types, namely Nematic,

Cholesteric and Smectic. These three classes are distinguished by the

different kinds of molecular order they exhibit.

[A] Nematic Structure :

The molecules in the nematic structure possessing only orientational but no positional long range order.

The behaviour of nematic liquid crystal is closer to the true “anisotropic‟ liquids. This liquid crystal exhibit normal liquid flow characteristic having low viscosity, they flow smoothly, yet is turbid and anisotropic.

The nematic structure is the highest temperature mesophasein thermotropic liquid crystal. In this structure, the molecules have no particularpositional order, but tend to point vertically in same direction.

Example:P-methoxybenzylideneP1-N-butyl-aniline,P-n-Hexyl-P1-cyano Biphenyl

[B] Smectic Structure:

The word “Smectic” is derived from the Greek word which means soap. The origine is explained by the fact that the thick, slippery substance often found at the bottom of a soap dish is actually type of smectic liquid crystal.

Another distinct mesophase of liquid crystal substance is the smectic state. In this phase, the molecules maintain the general orientational order not present in the nematic state.The smectic LC does not flow as normal liquids.

The optical observations indicated different structures for these smectic phases and therefore, there are A, B and C type of smectic liquid crystal.

(i) Smectic Liquid Crystal-A:

There are the few characteristics of Smectic-A :

 They do not show layered structure. The thickness of layer is very close to the

full length of the constituent molecules.

There is no long –range molecular order.

It is optically active.

Example: Ethylp-(P1-Phenyl benzylamine) benzoate

(ii) Smectic Liquid Crystal –B:

There are the few characteristics of Smectic-B :

 They formed layered structure and these layers appear to have a „periodicity‟ and „rigidity‟ of two dimensional liquids.

Molecular order is found in each layer of the LC.

The layers of smectic- B are not flexible.

Example: Ethyl P-ethoxy benzal-P1-aminocinnamate

(iii) Smectic Liquid Crystal-C:

There are the few characteristics of Smectic-C :

 They formed layered structure.

Each layer is still two dimensional liquid.

It is optically biaxial.

Example: P-n-octyloxy benzoic acid

[C] Cholesteric Liquid Crystal :

The cholesteric LC phase is typically composed of nematic mesogenic molecules containing chiral centre which produces intermolecular forces that favor alignment between molecules at a slight angle to another.

This leads to the formation of a structure which can be visualized as a stack of very thin 2-dimentional nematic-like layers with the director in each layer twisted with respect to those above and below.

Example: Cholesterylnonanoate

2. Lyotropic LC: When a high concentration of long organic molecules of rod-like shape is dissolved in an isotropic solvent like water, lytropic liquid crystals are formed. The long ranges ordering in these lyotropic LC are mainly due to the solvent –solute interaction. Example: Deoxyribonucleic acid , Tobacco mosaic virus, synthetic polypeptidies,Sodium stearate.

(B)Applications :

LCD device like Liquid crystal thermometer: Cholesreric LC reflect light with a wavelength equal to to pitch. Because the pitch is dependent upon temperature, the colour reflect also is dependent on temperature. LC makes it possible to accurately gauge temperature just by looking at the color of the thermometer.

Auto Dashboards, Radios & Clocks ,Computers ,Blood Pressure Indicators, Calculators Cameras, Digital Meters, Electronic Billboards, Exercise Equipment, Gasoline Pump Indicators ,Highway Signs.

 Non-destructive Testing: Cholesteric LC s are color sensitive with temp.

Biological Systems and Medicine: In medical thermography which provides information on the normal and abnormal functioning of the sensory and nervous system, vascular dysfunction

Radiation sensing: Thermal imaging as well as specialized LC thermal detectors has grown into an important technology that is applied directly by users on the ground or from flying aircraft. Using thermal sensors coupled with optical systems one is able to see in the dark by detecting varying temperatures from different

objects in the scene.

Analytical Instrumentsz

Que>3(B)

[I] Explain the preparation, properties and application of Plaster of Paris in detail.

Ans>

Preparation

 plaster of paris is prepared by heating gypsum (CaSO4.2H2O) at 120°C in rotary kilns, where it gets partially dehydrated.

 The temperature should be kept below 140°C otherwise further dehydration will take

place and the setting property of the plaster will be partially reduced.

Properties

 It is a white powder. When mixed with water (1/3 of its mass), it evolves heat and

quickly sets to a hard porous mass within 5 to 15 minutes. During setting, a slight

expansion (about 1%) in volume occurs so that it fills the mould completely and takes a

sharp impression. The process of setting occurs as follows:

Uses

 In surgery for setting broken or fractured bones

 For making casts for statues, in dentistry, for surgical instruments, and toys etc

 In making black board chalks, and statues

 In construction industry

QUE>

[II] Discuss the properties of good refractory materials for different applications in detail.

ANS>

à A good refractory material should have the following properties:

 It should be able to withstand high temperatures generated in the furnace.

 It should be able to withstand sudden alternating heating and cooling, i.e., thermal

shocks.

 It should be able to withstand abrasion and rough usage.

 Its contraction and expansion due to the inevitable temperature variation should be

minimum possible.

 It should be able to withstand fluxing action of the slags and the corrosive action of

gases.

 It should have good heat insulating properties.

 It should be chemically inactive at elevated temperatures.

 It should be impermeable to gases and liquids as far as possible.

 If used in electric furnaces, it must have low electrical conductivity.

Que>4(A)

Explain the complexometric method for estimation of hardiness in water sample with the calcilation.

Ans>

The complexometric method is a common method used for the estimation of hardness in water. The method involves the formation of a complex between the metal ion present in the water and a complexing agent, also called a chelating agent. The complexing agent used is usually ethylenediaminetetraacetic acid (EDTA), which has a high affinity for metal ions. The steps involved in the complexometric method for estimation of hardness in water are as follows:

Sample Collection: Collect a water sample to be tested for hardness. The sample should be representative of the water source being tested.
Sample Preparation: Adjust the pH of the sample to around 10 using a buffer solution. This is done to ensure that the metal ions present in the sample are in their free ion form, which is necessary for the complexation to occur.
Titration: Add a small amount of indicator solution to the sample. The indicator used is usually a dye called Eriochrome Black T, which changes color from blue to wine red when it forms a complex with the metal ions. Then, add a standardized solution of EDTA to the sample until the color of the indicator changes from blue to wine red. The volume of EDTA solution required to reach the end-point is noted.
Calculation of Hardness: The hardness of the water sample is calculated using the formula:

Hardness (in mg/L) = (Volume of EDTA x Normality of EDTA x 1000)/Volume of Sample

The normality of EDTA is known, and the volume of the sample is measured. The hardness of the water sample is expressed in terms of milligrams per liter (mg/L) of calcium carbonate (CaCO3) equivalent.

Que>4(B)

[II] 0.25g of CaCO was dissolved in dil. HCl and then diluted up to 250 ml. 50ml of this solution requires 50ml of EDTA solution for titration. 50ml of hard water sample require 20 ml same EDTA solution for titration. 50ml of same hard water sample on boiling and filtering consumed 10ml of EDTA for titration. Calculate total, carbonate and non-carbonate hardness.

Ans>

Que>4(B)

[II] Discuss the Zeolite method with its suitable diagram, reaction and procedure for water purification.

Ans>

Zeolites are naturally occurring sodium aluminum silicates having different amounts of water of crystallization. They are represented as Na2O.Al2O3.xSiO2.yH2O where x and y varies from 2 to 10 and 2 t 6 respectively. They have the property of exchanging their Na ions for hardness causing ions like Ca⁺⁺ and Mg⁺⁺

Ca(HCO3)2+Na₂Ze→CaZe+2NaHCO3

MgSO4+Na2Ze→MgZe+Na2SO4

CaCl2+Na₂Ze→CaZe+2NaCl

where Ze represents zeolite.

The Ze mineral gets exhausted when all the Na⁺are replaced by Ca⁺⁺ and Mg⁺⁺ ions. Now Ze can be regenerated by passing Nacl solution,

CaZe+2NaCl→CaCl₂+Na₂Ze

MgZe+2NaCl→MgCl₂+Na₂Ze

The regenerated Ze can now be used for replacing Ca⁺⁺and Mg⁺⁺ from hard water. Zeolite softening is carried out in large cylindrical tank as shown, holding ze material on a perforated platform. The tank has two inlets for feeding raw water and passing saturated NaCl solution.

Limitations-

1) Raw material must be free from turbidity and suspended impurities.

2) Highly acidic water is not suitable as it affects mineral.

3) Zeolites of iron and manganese cannot be easily regenerated by passing NaCl solution. Hence iron and manganese impurities in the water to be treated must be minimum.

Advantages-

1) Water of about less than 15 ppm is obtained.

2) The process automatically adjusts for different hardness of incoming water.

3) Water obtained is quiet clear.

4) The equipment is compact and requires less space.

5) It requires less skill in maintenance as well as operation.

Any Four

Que>5 (A) Write a short note on chromic material in detail.

Ans>

Introduction:

Chromic material is made by a process that induces a change in the colors of compounds. The process is called as a Chromism .In most cases; chromism is based on a change in the electron states of molecules.

 Classification of chromic materials :

 Thermochromic material is induced by heat, that is a change of temperature.

Example: Cu2HgI4 is red at 200C but black at 700C, ZnO is white at room temperature but yellow at higher temperatures

 Photochromic material is induced by light irradiation. This phenomenon is based on the isomerization between two different molecular structures, light-induced formation of color centers in crystals, precipitation of metal particles in a glass, or other mechanisms. Example : piropyrans, spirooxazines

 Electrochromic material is induced by the gain and loss of electrons. This phenomenon occurs in compounds with redox active sites, such as metal ions or organic radicals. Example :arbazoles, methoxy biphenyls, fluorenones, benzoquinones, napthoquinones and anthraquinones

 Solvatochromic material is depends on the polarity of the solvent. Most solvatochromic compounds are metal complexes.

Applications:

 Plastic lenses for sunglasses

 children‟s toys

 logos on T-shirts, lunch boxes, crayons, jelly shoes, hair clips,

craft beads,

 PVC belts, watchbands,

 Drinking straws, spoons, cups, combs,

 Greeting cards, stickers and business cards.

 Environmental control of the temperature of a building using

smart glazing in windows.

Que>5 (B)Give the application of Nano materials.

Ans>

Nanoscale materials are defined as a set of substances where at least one dimension is less than approximately 100 nanometers. A nanometer is one millionth of a millimeter – approximately 100,000 times smaller than the diameter of a human hair.

 Nanomaterials are of interest because at this scale unique optical, magnetic, electrical, and other properties emerge. These emergent properties have the potential for great impacts in electronics, medicine, and other fields.Classification of nanomaterials based on structure.

 Nanomaterials have extremely small size which having at least one dimension 100 nm or less. Nanomaterials can be nanoscale in one dimension (eg. surface films), two dimensions (eg. strands or fibres), or three dimensions (eg. particles).

 They can exist in single, fused, aggregated or agglomerated forms with spherical, tubular, and irregular shapes. Common types of nanomaterials include nanotubes, dendrimers, quantum dots and fullerenes. Nanomaterials have applications in the field of nano technology, and displays different physical chemical characteristics from normal chemicals (i.e., silver nano, carbon nanotube, fullerene, photocatalyst, carbon nano, silica).

 According to Siegel, Nanostructured materials are classified as Zero dimensional, one dimensional, two dimensional, three dimensional nanostructures.

Que>5 (C)Give the difference between Dry process and Wet process of cement manufacturing.

Ans>