QUE 1>
A> Green Chemistry is an approach to designing chemical processes and products that aim to minimize or eliminate the use and generation of hazardous substances. The principles of Green Chemistry are:
- Prevention: It is better to prevent waste and pollution at the source than to clean it up after it is formed.
- Atom economy: Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product, minimizing waste and reducing the use of hazardous substances.
- Less hazardous chemical syntheses: Synthetic methods should be designed to use and generate substances that have minimal toxicity, are renewable, and are biodegradable.
- Designing safer chemicals: Chemical products should be designed to have little or no toxicity, and should be made from renewable materials whenever possible.
- Safer solvents and auxiliaries: The use of auxiliary substances such as solvents, separation agents, and catalysts should be minimized and should be selected to be as benign as possible.
B> The hydroxide, carbonate, and bicarbonate ions can be estimated by titration method. A known volume of water sample is titrated with standard acid solution using suitable indicators. The hydroxide ions are determined by direct titration with standard acid using phenolphthalein as an indicator. The carbonate and bicarbonate ions are determined by back titration method. The carbonate and bicarbonate ions are first reacted with excess standard acid and then the excess acid is back-titrated with standard alkali using methyl orange as an indicator. The concentration of hydroxide, carbonate, and bicarbonate ions in the water sample can be calculated based on the volume of standard acid and alkali used in the titration.
C> The rate of corrosion process is influenced by several environmental factors such as temperature, humidity, pH, dissolved oxygen, salinity, and the presence of other corrosive substances in the environment. Higher temperatures and humidity can accelerate corrosion rates, while low pH and dissolved oxygen can enhance the process. Salinity can increase the rate of corrosion, while pollutants and corrosive substances such as acids and salts can also contribute to the corrosion process. Understanding and controlling these environmental factors can help in preventing corrosion and preserving materials.
QUE 2>
A> Green synthesis is a valuable method for producing eco-friendly and sustainable materials in a cost-effective manner. Some of the applications of green synthesis include the production of pharmaceuticals, cosmetics, and agrochemicals. It is also used in the synthesis of nanoparticles, which have applications in drug delivery, imaging, and other fields.
The traditional method for extracting gold from its ore involves the use of cyanide, which is toxic and poses a serious threat to the environment. On the other hand, the greener method for gold extraction involves the use of non-toxic reagents such as thiosulfate, which is safer and more sustainable. This method also requires less energy and produces less waste, making it an environmentally friendly alternative to the traditional method.
B> Electrodes are critical components in electrochemical analysis, and there are different types of electrodes used for different purposes:
1.Reference electrodes: These electrodes provide a stable and known potential against which other electrodes can be measured. Examples include the Standard Hydrogen Electrode (SHE), the Silver/Silver Chloride Electrode, and the Calomel Electrode.
2.Indicator electrodes: These electrodes respond to changes in the analyte concentration and generate a signal that can be detected. Examples include the Glass Electrode, which is used to measure pH, and the Ion-Selective Electrode, which measures specific ion concentrations.
3.Working electrodes: These electrodes are placed in contact with the analyte and are used to generate or measure the electrochemical signal. Examples include the Platinum Electrode, which is commonly used for electrochemical reactions, and the Carbon Electrode, which is used in applications such as electroanalysis and energy storage.
4.Counter electrodes: These electrodes are used to complete the circuit in an electrochemical cell and provide a surface for the counter reaction. Examples include the Platinum Electrode and the Graphite Electrode.
B>First, let’s calculate the amount of soda and lime required to treat the given water:
Calculation for Soda:
Given that the concentration of NaCl in water is 20 mg/ltr and 1 molecule of NaCl reacts with 1 molecule of soda (Na2CO3) to form 2 molecules of NaCl and 1 molecule of Na2CO3.
Number of moles of NaCl in 80,000 ltr of water = (20 mg/ltr) x (80,000 ltr) / (1000 g/kg) / (58.5 g/mol)
= 544.22 mol Therefore, number of moles of Na2CO3 required = 544.22 / 2 = 272.11 mol
Now, since the soda is impure (17% impure), we need to adjust the amount of soda required accordingly. Let’s assume that the impurities are inert and do not take part in the reaction with NaCl.
Therefore, the amount of impure soda required = (272.11 mol) / (0.83) = 327.6 mol
Weight of impure soda required = (327.6 mol) x (106 g/mol) = 34,716 g
Calculation for Lime:
Given that the concentration of CaCO3 in water is 40 mg/ltr and 1 molecule of CaCO3 reacts with 2 molecules of lime (Ca(OH)2) to form 1 molecule of CaCO3 and 2 molecules of Ca(OH)2.
Molecular weight of CaCO3 = 100 g/mol
Molecular weight of Ca(OH)2 = 74 g/mol
Number of moles of CaCO3 in 80,000 ltr of water = (40 mg/ltr) x (80,000 ltr) / (1000 g/kg) / (100 g/mol)
= 320 mol Therefore, number of moles of Ca(OH)2 required = 320 x 2 = 640 mol
Now, since the lime is impure (14% impure), we need to adjust the amount of lime required accordingly. Let’s assume that the impurities are inert and do not take part in the reaction with CaCO3.
Therefore, the amount of impure lime required = (640 mol) / (0.86) = 744.18 mol
Weight of impure lime required = (744.18 mol) x (74 g/mol) = 55,054 g or 55.054 kg
Therefore, 34.716 kg of impure soda and 55.054 kg of impure lime are required to treat 80,000 ltr of water with the given impurity percentages.
B> Ion-exchange or Deionization or Demineralization Process – Recently ion-exchange resins have been used to remove all minerals from water. It is a process by which ions held on a porous, essentially insoluble solid are exchanged for ions in solution that is brought in contact with it.
Ion-exchange Resin – An ion-exchange resin is a crosslinked organic polymer network having some ionisable group. It may be of two types depending upon the nature of the ionizable group.
(i) Cation Exchange Resin or Cation Exchanger – Such resins have – SO3H, — COOH or -OH (phenolic) group as the ionizable group. Since these resins exchange the cationic portion of minerals by their hydrogen atom, they are known as cation exchangers.
(ii) Anion Exchange Resin or Anion Exchanger – These resins have -NH2, -NHCH3, -N(CH3)2 or -OH group. They exchange the anionic portion of the minerals and they are known as anion exchanger.
Uses of Ion-exchange Resin – Water treatment by ion-exchange resin includes softening deionization and de-alkalization of water. Therefore, hard water can be converted into soft water by making use of ion-exchange resins.
Process – In this process first we passed hard water through cation exchange column, which removes all the cations (like Ca+2, Mg+2 etc.) from it and equivalent amount of H+ ions are released from this column to water.
Thus,
2RH+ + Ca+2 -> R2Ca+2 + 2H+
2RH+ + Mg+2 -> R2Mg+2 + 2H+
After this process, hard water is passed through anion exchange column, which removes all the anions (like SO4-2, Cl– etc.) from it, and equivalent amount of OH– ions are released from this column to water. Thus,
R’OH-2 +Cl-2 -> R’Cl–+ OH–
2R’OH- + SO2-4 -> R‘2 SO2-4 + 2OH–
2R’OH- + CO2-3 -> R‘2 CO2-3 + 2OH–
H+ and OH – ions get combined to produce water molecule
H+ + OH– + H2O
The water coming out from the exchanger is free from cations as well as anions. Ion-free water is known as a deionized or demineralized water.
QUE 3>
A> 1. Salt bridge: A tube or a strip of a porous material that connects the two half-cells of an electrochemical cell, allowing the exchange of ions to maintain charge neutrality and electrical continuity.
2.Electronegativity: The ability of an atom in a molecule to attract shared electrons towards itself.
3. Electra Affinity: The energy released when an atom or ion gains an electron to form a negatively charged ion.
4.Ionization Energy: The energy required to remove an electron from an atom or a positive ion.
5.Electromotive force: The energy per unit charge that is generated by an electrochemical cell, measured in volts (V). It is also known as the cell potential or voltage.
A> Impressed Current Method: This method involves the use of an external power source to provide a continuous supply of current to the metal structure, which helps to prevent corrosion. The current is passed through the metal structure to counteract the natural electrochemical reactions that lead to corrosion. This method is used in large structures such as pipelines, storage tanks, and ships.
Sacrificial Anodic Method: In this method, a more reactive metal is connected to the metal structure that needs protection. The more reactive metal (called the sacrificial anode) corrodes preferentially to the metal structure, thereby protecting it from corrosion. Examples of sacrificial anodes include zinc, aluminum, and magnesium. This method is commonly used in small structures such as boats, underground tanks, and water heaters.
Both methods are effective in preventing corrosion, but their choice depends on the nature of the structure, the environment in which it operates, and the economic considerations involved.
B> The Standard Hydrogen Electrode (SHE) is a reference electrode commonly used in electrochemistry to measure the electrochemical potential of other electrodes. It consists of a platinum electrode coated with a layer of platinum black, which provides a large surface area for hydrogen gas to be adsorbed. The electrode is immersed in an acidic solution of known concentration, usually 1M HCl. The half-reaction at the electrode is:
2H+ + 2e- -> H2
The SHE has a potential of exactly 0 V at standard conditions (25°C, 1 atm pressure of H2 gas, and 1 M H+ concentration). By convention, the SHE is assigned a potential of 0 V at all temperatures and pressures, and all other electrode potentials are measured relative to it. The SHE is also used as the reference electrode in the Nernst equation, which relates the potential difference between two electrodes to the concentration of the species involved in the redox reaction.
c>
The corrosion which takes place in the absence of moisture or water is called Dry corrosion. It is uniform corrosion. This happens due to the direct interaction of atmospheric components such as O2, X2, SO2, NO2, H2S, etc with the metallic materials in the absence of moisture. This can be discussed under basic three categories.
1) Corrosion due to oxygen
Alkali and alkaline earth metals react with oxygen at room temperature. Other metals except Ag, Au, Pt react with oxygen at elevated temperature.
Further interaction depends on the nature of the oxide film formed.
Stable film: If the oxide film is stable , it remains adhered to the surface strongly. This prevents further penetration of oxygen to the base metal. Egg. In case of oxides of Al, Pb, Cu etc.
Unstable film: If the oxide formed is unstable, it dissociates back to metal and oxygen. Therefore corrosion does not take place. E.g., Oxides of Ag, Au, Pt.
Volatile: If the oxide film is volatile, it gets volatized to expose new surface to interact with oxygen. Here corrosion continues to eat the whole metallic structure. Therefore corrosion is rapid and continuous, e.g., oxide of molybdenum.
Porous: Here the oxide film has pores or channels through which oxygen slowly diffuses to interact with the base metal. Therefore in this case corrosion is slow but continuous. E.g., Oxide of iron
2) Corrosion due to other corrosive gases:
The extent of corrosion depends on the chemical affinity between the base metal and the atmospheric components.
3) Liquid metal corrosion
This type of corrosion occurs when a molten liquid is passed continuously on a solid Metal/alloy surface. The corrosion is attributed to either dissolution of the molten liquid Into the solid metal phase.