Vidyalankar F.Y. Diploma : Sem. II [CD/CM/CO/CW/DE/ED/EE/EI/EJ/EN/EP/ET/EV/EX/IC/IE/IF/IS/IUMU] Applied Chemistry

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1 F.Y. Diploma : Sem. II [CD/CM/CO/CW/DE/ED/EE/EI/EJ/EN/EP/ET/EV/EX/IC/IE/IF/IS/IUMU] Applied Chemistry Time : 2 Hrs. Prelim Question Paper Solution Marks : 50 Q.1Attempt any NINE of the following: [18] Q.1(a) What are the constituents of copper matte? [2] Constituents : Mixture of molten Cu 2 S( Copper sulphide) FeS(Ferrous sulphide) traces. Q.1(b) State the two function of pigment. [2] (i) Provide opacity and colour to paint film. (ii) Give strength to the film. (iii)give protection to the paint film by reflecting harmful ultraviolet light. (iv) Provide resistance to paint film against abrasion, moisture and weather. (v) Give an aesthetical appeal (i.e pleasing to look at) to the paint film. Q.1(c) Write chemical reaction of formation of slag during smelting cu ore. [2] Copper dissolves in these acids with the formation of complex salts. e.g., 2Cu + 2HBr 2CuBr + H 2 2CuBr + 2HBr H 2 [Cu 2 Br 4 ] Q.1(d) Define the terms: [2] (i) Specific conductance (ii) Equivalent conductance (i) Specific conductance (k) : Specific conductance is the conductance of a 1 cm 2 of the substance or solution. OR The conductance offered by a solution of unit length & area of unit cross section is known as specific conductance. (ii) Equivalent conductance (v) : It is the conductance of the solution containing 1 gm equivalent of solute / electrolyte when placed between two sufficiently large electrodes 1 cm apart. Q.1(e) Write two applications of phenol formaldehyde resin as an adhesive. [2] (i) Used as adhesive for grinding wheels & brake linning. (ii) Used for decorative laminates wall covering & industrial laminates for electrical parts. (iii)used for making water-proof plywoods. (iv) Used in bonding articles in air craft and ship building. Q.1(f) Define corrosion. State the types of corrosion. [2] Corrosion: Any process of chemical or electrochemical decay or destruction of a metal due to the action of surrounding medium is called as corrosion. Types of corrosion (i) Atmospheric corrosion or direct chemical corrosion or Dry corrosion. (ii) Immersed corrosion or electro chemical corrosion or wet corrosion. Q.1(g) State the type of oxide film which is more protective towards corrosion with one example. More protective oxide films Examples: Stable nonporous oxide film Aluminium, Copper, Chromium etc. Unstable oxide film Gold, Silver, Platinum etc. [2] 1

2 : F.Y. Diploma Chemistry Q.1(h) Define liquid crystal polymers. [2] Liquid crystal polymers are a class of aromatic polyester polymers which are capable of forming regions of highly ordered structure (like crystal) even in the liquid phase. Q.1(i) Differentiate between dielectrics and insulators. [2] Dielectrics Insulators (i) The materials which are used to Insulators or insulating materials are the prevent the loss of electricity through substances which retard the flow of heat or certain parts of an electrical system are electricity or sound through them. known as dielectrics. (ii) The main function is storage of The main function of such materials is that electrical charge. (iii) All dielectrics are insulators because they avoid the flow of electric current through them. (iv) Examples : Air, N2 gas, CO2 gas, Silicon fluid etc of insulation. All insulators are not dielectrics because they can not store charges like dielectrics Examples: Rubber, Plastics etc. Q.1(j) List characteristics of Ni-Cd storage cell. [2] Characteristics of NiCd storage cell : (i) Each cell has an e.m.f. of 1.4V when fully charged. (ii) It has low internal resistance and longer life. (iii) It is expensive in cost. (iv) It can be recharged because no products are lost & no gas is evolved. Q.1(k) Write two applications of Teflon. [2] Teflon or Fluon Polytrifluoro-chloro-ethylene: (i) It is an ideal dielectric material with dielectric constant of 2 to 2.2. (ii) It is generally most thermally and chemically stable. It is stiff and so must be used in thin layers. Q.1(l) Give two limitations of Adhesive bonding. [2] Limitations of adhesive bonding (i) Because most of adhesives are organic materials, so they cannot be used at high temperatures and their bond strength decreases rapidly as the temperature rises. (ii) There is no single general purpose adhesive, which can join all types of surfaces. So for a particular job particular suitable adhesive is required and this may also require particular bonding conditions. Hence, careful selection of an adhesive, for each set of substances to be bonded is necessary. Q.2Attempt any FOUR of the following : [16] Q.2(a) How copper is obtained from its ore by smelting process? Write it with labeled diagram. [4] 2

3 Prelim Question Paper Solution Process: (i) Roasted copper ore is then mixed with coke & sand particles & then strongly heated at high temperature in a water jacketed blast furnace. (ii) At high temperature ferrous sulphide (FeS) is oxidised & converted into ferrous oxide (FeO) which further reacts with sand particles to form a fusible slag (FeSiO 3 ) 2FeS +3O 2 2FeO + 2SO 2 FeO + SiO 2 FeSiO 3 (iii)further cuprous oxide (Cu 2 O) formed during roasting combines with ferrous sulphide (FeS) to form ferrous oxide (FeO) & cuprous sulphide (Cu 2 S). The ferrous oxide (FeO) formed futher react with silica particals to form slag. Cu 2 O + FeS FeO + Cu 2 S (iv)thus during smelting process most of the ferrous sulphide impurity is converted into the fusible slag (FeSiO 3 )which is then removed from the upper slag outlet. (v) The molten mass containing mostly cuprous sulphide (Cu 2 S) & little quantity of ferrous sulphide (FeS) is called as matte which is then removed from the lower outlet. Q.2(b) Write mechanism of corrosion of metal due to action of oxygen. [4] Mechanism of corrosion of metal due to action of oxygen Differential aeration accounts for the corrosion of metals, partially immersed in a solution, just below the waterline. Thus, if a metal (say Zn) is partially immersed in a dilute solution of a neutral salt (say NaCl) and the solution is not agitated properly, then, the parts above and closely adjacent to the waterline are more strongly aerated (because of the easy access of oxygen) and hence, become cathodic. On the other hand, parts immersed to greater depth (which have less access of oxygen) show a smaller oxygen concentration and thus, become anodic (see figure 1). So, a difference of potential is created, which causes a flow of current between the two differentially-aerated areas of the same metal. Zinc will dissolve at the anodic areas, and oxygen will take up electrons at the cathodic areas to form hydroxyl ions. 2 ZnZn 2e (Oxidation) 1 O 2 H 2 O 2e 2OH (Reduction) 2 The circuit is completed by migration of ions, through the electrolyte, and flow of electrons, through the metal, from anode to cathode. In a similar way, iron corrodes under drops of water (or slat solution). Areas covered by droplets, having no access of oxygen, become anodic with respect to the other areas, which are freely exposed to air (see figure 2) Fig. 1 : Mechanism of differential aeration attack caused by partial immersion of a metal 3

4 : F.Y. Diploma Chemistry Fig. 2 : Mechanism of differential aeration attack, caused by the presence of drops of salt solution on the iron surface. Metal dissolves at the less-aerated anodic areas; whereas corrosion product (iron hydroxide) is deposited at the cathodic areas. Q.2(c) State composition properties and applications of Tinmann's solder or rose metal. [4] Solder Composition Properties Applications Tinmann's Sn = 66 % 1. It melts at 180C. It is used for joining articles of tin. solder: Rose metal Pb = 34 % Bi = 50% Pb = 28% Sn = 22% 1. It is easily fusible alloy. 2. Its melting point is 89C 1. It is used for making fire alarms. 2. It is used in electrical fuse wires, 3. It is used for casting for dental works. 4. It is used in automatic sprinkler system. Q.2(d) Describe the process of electrolytic reduction of A1. [4] The pure alumina is bad conductor of electricity & its melting point is 20000c. Hence electrolytic reduction of alumina is carried out in presence of cryolite because the presence of cryolite decreases the melting point of alumina & also increases its electrical conductivity. Carbon anodes Carbon lining Steel Sheets Lining of fire brick Na 3 AlF 6 + Al 2 O 3 Anode + Glow Lamp _ Cathode Coke Powder Fused cryolite + Alumina Al(molten Aluminum) Process: Figure shows electrolytic reduction of alumina(al2o3) (i) Alumina is dissolved in fused cryolite and electrolyzed in an iron tank lined inside with carbon which acts as cathode. (ii) The anode consists of number of carbon rods, suspended vertically from the copper clamps. (iii)the electrolyte is a mixture of alumina and cryolite. The temp of electrolyte bath is kept at about C iv. On passing current, alumina decomposes to aluminium and oxygen. 2 Al 2 O 3 4Al + 3O 2 (vi) The molten aluminium gets collected at the bottom of the cathode, while oxygen formed at anodes gets oxidized to CO and CO2. The process is continuous and fresh quantity of Al2O3 is added time to time. L 4

5 Prelim Question Paper Solution Q.2(e) Describe the hydrogen evolution mechanism of immersed corrosion. [4] Steel tank: Anode, Cu strip:- Cathode These types of corrosion occur usually in acidic environments like acidic industrial waste, solutions of non oxidizing acids. Process: Consider a steel tank containing acidic industrial waste and small piece of copper scrap. The portion of the steel tank in contact with copper becomes anodic and is corroded most with the evolution of hydrogen gas at cathodic area (copper piece). At anode Fe Fe e (Oxidation) These electrons flow through the metal from anode to the cathode At cathode H + ions are eliminated as H 2 gas 2H e H 2 (Reduction) Thus, over all reaction is Fe + 2H + Fe ++ + H 2 Q.2(f) Describe sherardizing process for protection of small articles of iron from corrosion. Write its applications. Sherardizing (i) The iron articles (bolts, screws, nails etc) to be coated are first cleaned and then packed with Zn dust and ZnO powder in a steeldrum, which is provided with electrical heating arrangement. (ii) The drum is slowly rotated for 2-3 hrs. and it s temp. is kept between C. (iii)during this process Zn slowly diffuses into iron surface forming Fe - Zn alloy at the surface which protects iron surface from corrosion. Applications: It is used for protecting small steel articles like bolts, screws, nuts, threaded parts, washers, valves, gauge, tools etc. Q.3Attempt any FOUR of the following : [16] Q.3(a) Write construction and working of Ni-Cd cell with labeled diagram. [4] Atmospheric corrosion: This type of corrosion occurs when metal surface comes in immediate contact directly with atmospheric gases like O 2, Cl 2, Br 2, I 2, H 2 S, CO 2, SO 2, NO 2 etc. Mechanism: Metallic surfaces when exposed to air undergo oxidation and the process of corrosion is represented by the equation. [4] 5

6 : F.Y. Diploma Chemistry 2M + O 2 2MO (Metal Oxide) (Metal) (Oxygen) A thin oxide layer is formed on the metal surface and the nature of this film decides further action depending upon the film so produced. 2 MM 2e (lossof electrons) Metalion 2 O2e O (gainof electrons) 2 2 MO M O MO(MetalOxide) Mechanism of Atmospheric Corrosion Q.3(b) Give construction and working of hydrogen-oxygen fuel cell. [4] OR OR Construction: (i) Positive plates are made up of nickel plated tubes, containing a mixture of nickel oxide (NiO 2 ) & hydroxide + 17% flakes of graphite or metallic nickel for increasing conductivity. (ii) They also contain an activated additive 2% Ba(OH) 2 which increases the life of plates. Negative plates consist of spongy Cadmium. (iii) The electrolyte is 20-15% solution of KOH to which small quantity of lithium hydroxide (LiOH) is added to increase the capacity of cell. Working: Discharging: Positive Plate: NiO 2 (s) + 2H 2 O (l) + 2e - Ni (OH) 2 (s) + 2OH - Negative Plate: Cd (s) + 2OH - (aq) Cd (OH) 2 (s) + 2e - Net reaction: NiO 2 (s) + Cd(s) + 2H 2 O Ni(OH) 2 + Cd(OH) 2 6

7 (B) Charging: Positive Plate: Ni(OH) 2 (s) + 2OH - (a) NiO 2 (s) + 2H 2 O + 2e - Negative Plate: Cd(OH) 2 (s) + 2e - Cd(s) + 2OH(s) Net reaction: Ni(OH) 2 + Cd(OH) 2 NiO 2 (s) + Cd(s) + 2H 2 O Thus, discharging & charging reactions can be shown simultaneously as:- NiO 2 (s) + Cd (s) + 2H 2 O 2Ni(OH) 2 + Cd(OH) 2 OR Discharging: Positive Plate: NiO(OH) + 2H 2 O + 2e - 2Ni (OH) 2 + 2OH - Negative Plate: Cd + 2OH - Cd (OH) 2 + 2e Net reaction: NiO(OH) + Cd + 2H 2 O 2Ni(OH) 2 + Cd(OH) 2 (B) Charging: Positive Plate: Ni(OH) 2 + 2OH - NiO(OH) + 2H 2 O + 2e - Negative Plate: Cd(OH) 2 + 2e - Cd + 2OH - Net reaction: Ni(OH) 2 + Cd(OH) 2 NiO(OH) + Cd + 2H 2 O Thus, discharging & charging reactions can be shown simultaneously as: NiO(OH) + Cd (s) + 2H 2 O 2Ni(OH) 2 + Cd(OH) 2 Prelim Question Paper Solution Q.3(c) Describe the construction and working of lead - Acid storage cell. [4] Construction: 1. It consist of several lead plates which are connected to each other & are acting as a Anode (-ve electrode) 2. It consist of several lead oxide plates which are connected to each other & are acting as a Cathode (+ve electrode) 3. 20% H2SO4 Solution having sp.gravity1.15 at 25 0C is used as an electrolyte 4. Lead & lead oxide plates are separated from each other by strips of insulating materials like wood or rubber or glass fiber. 7

8 : F.Y. Diploma Chemistry Working: (i) Discharging: - While discharging chemical energy gets converted into electrical energy. At Anode: Pb Pb e (Oxidation) Pb 2+ + SO 2-4 PbSO 4 At Cathode: PbSO 2 + 4H + + 2e - Pb H 2 O (Reduction) Pb 2+ + SO 2-4 PbSO 4 Net reaction during is discharging:- Pb + PbO 2 + 4H + + 2SO 2-4 2PbSO 4 + 2H 2 O Lead sulphate is precipited at both the electrodes. The voltage of each cell is 2.0 volts at 25C. (ii) Charging:- To recharge a lead storage cell, the reactions taking place during discharging are reversed by passing an external e.m.f. greater than 2 volts from a generator. At Cathode: PbSO 4 + 2e - Pb + SO 4 2- At Anode: PbSO 4 + 2H 2 O PbO 2 + 4H + + SO e - Net reaction during Charging: 2PbSO 4 + 2H 2 O Pb + PbO 2 + 4H + + 2SO 4 2- During the process of charging, the electrodes of the cell are restored to their original conditions (to Pb and PbO 2 respetively). Q.3(d) Define adhesives with two examples. Write any two advantages. [4] Adhesives:Any substance which is capable of holding the materials together by surface attachment is called as an adhesive. Examples:- Epoxy resins, Urea formaldehyde, Phenol formaldehyde Advantages: (i) Adhesives have advantages of joining material such as glass & metal, metal metal, metal & plastic, plastics-plastic, ceramic & ceramic. (ii) Surfaces are easily & rapidly attached to each other by adhesives. (iii)adhesives introduce heat as well as electrical insulating layers in between the bonding surfaces (iv) The process of applying adhesives is very simple, so it does not require highly specialized person. (v) In several cases of bonding by adhesives, no high heat is required. (vi) Adhesive bonding requires less after finishing as compared with other joining processes such as welding, soldering etc. (vii) Metal joined by an adhesive can resist corrosion. (viii)adhesive joints are leak proof for gases & liquids. So adhesive bonding is used in preparing water light wood boats (ix) The structural members joined by adhesives are free from any residual stress which makes it possible to fully utilize the inherent strength of any material. Q.3(e) State two properties and two uses of silicone fluids. [4] Properties : 1. They can be used in temperature range of - 90C to 220C 2. They have excellent dielectric properties over a wide range of temperature 3. They have high heat stability & good oxidation resistance 4. They are non corrosive to metals up to 200 0C, fire proof.non toxic, chemically inert & odourless 8

9 Prelim Question Paper Solution 5. They have excellent water repellency 6. Their viscosity does not change readily with the change in temperature. 7. They are chemically inert. 8. They are non-greasy, non-irritating and odourless. 9. They have tendency to break down and give considerable amounts of gases (H 2 ) and residue which mainly contains carbon, silicon, carbide and SiO 2. Because of this drawback silicone fluids are not suitable to be used as switchgear oils. Uses: 1. As a lubricant: excellent lubrication for plastic and elastomeric surfaces. 2. In polishes and chemical specialities: It is used in automobile and furniture polishes due to its high gloss and water repellency. 3. As a mechanical fluid: It is used as hydraulic or transformer oils, damping mediums. 4. As coolant: They are used as coolant in radio, pulse and aircraft transformers. 5. As a foam preventive: effectively control foam in many machines like photocopiers and laser printers. 6. Also used in cosmetic and pharmaceutical industries. 7. In electrical and chemical specialities: Used as an insulator in medium and high voltage applications i.e. in transformers. 8. As a release material: an odourless, non-toxic, noncarbonizing moulds release for rubber, plastics and metal die castings. Q.3(f) Write for properties and applications of urea-formaldehyde resin. [4] Properties : (i) The bond film produced by urea formaldehyde resin is quite rigid & transparent. (ii) It is good resistant to moisture, insects & fungi. (iii) However action of acids & alkalies deteriorate the resin film after some time. (iv) It can be used in cold but a little heating helps in accelerating the setting process. Applications: (Any two) (i) Used for bonding wooden surfaces. (ii) Used for bonding water proof plywood, laminates. (iii) Bonding articles in aircraft & ship building industries etc. 9