GTU Maths Paper Solution

# Gujarat Technological University (GTU) ## BE - Semester I & II Examination – Summer 2025 ### Subject: Chemistry (Subject Code: 3110001) --- ## Question 1 ### Q.1 (a) Define the following terms: Chemistry, Ions, Atomic Size [03 Marks] #### 1. Chemistry Chemistry is the branch of physical science that deals with the study of the composition, structure, properties, and reactions of matter, along with the energy changes that accompany these processes. #### 2. Ions Ions are chemically charged species (atoms or groups of atoms) formed when a neutral atom/molecule either loses or gains one or more electrons. * **Cation:** A positively charged ion formed by losing electrons (e.g., $\text{Na}^+$). * **Anion:** A negatively charged ion formed by gaining electrons (e.g., $\text{Cl}^-$). #### 3. Atomic Size Atomic size (or atomic radius) is defined as the distance from the center of the nucleus of an atom to the outermost shell containing valence electrons. --- ### Q.1 (b) Discuss the periodic property for a periodic table. [04 Marks] Periodic properties are the characteristics of elements that show a regular, repeating pattern (trend) when elements are arranged in order of increasing atomic number in the periodic table. #### Key Periodic Properties and Trends ``` --- Decreases ---> (Atomic Radius) <--- Increases --- (Ionization Energy, Electronegativity) +-------------------------------------------------------------+ | | | | | | | | | I | D n | e c | c r | r e | e a | a s | s e | e s | s | | | | v (Atomic Radius) (IE, Electronegativity) v | +-------------------------------------------------------------+ ``` ##### 1. Atomic Radius * **Definition:** The distance from the nucleus to the outermost electron shell. * **Trend in a Period:** **Decreases** from left to right because the effective nuclear charge increases, pulling the electrons closer to the nucleus. * **Trend in a Group:** **Increases** from top to bottom due to the addition of new electronic energy shells. ##### 2. Ionization Energy (IE) * **Definition:** The minimum energy required to remove the most loosely bound electron from an isolated gaseous atom. * **Trend in a Period:** **Increases** from left to right due to smaller atomic size and stronger nuclear hold on electrons. * **Trend in a Group:** **Decreases** down the group because the valence electrons are farther from the nucleus and easier to remove. ##### 3. Electronegativity * **Definition:** The tendency of an atom in a molecule to attract shared pairs of electrons towards itself. * **Trend in a Period:** **Increases** from left to right. * **Trend in a Group:** **Decreases** down the group. ##### 4. Electron Affinity * **Definition:** The energy released when an electron is added to a neutral gaseous atom. * **Trend in a Period:** Generally becomes **more negative (increases)** from left to right. * **Trend in a Group:** Becomes **less negative (decreases)** down the group. --- ### Q.1 (c) Explain chemical bondings with suitable examples. [07 Marks] A chemical bond is the attractive force that holds atoms, ions, or molecules together to attain stability (by completing their octet/duplet configurations). The major types of chemical bonding are: #### 1. Ionic (Electrovalent) Bond Formed by the complete transfer of one or more valence electrons from a metal atom (which becomes a cation) to a non-metal atom (which becomes an anion). The bond is held together by strong electrostatic forces of attraction. * **Example: Sodium Chloride ($\text{NaCl}$)** * Sodium ($\text{Na}$, $Z=11$, configuration: $2, 8, 1$) loses $1$ electron to achieve stability: $$\text{Na} \rightarrow \text{Na}^+ + e^-$$ * Chlorine ($\text{Cl}$, $Z=17$, configuration: $2, 8, 7$) gains this $1$ electron: $$\text{Cl} + e^- \rightarrow \text{Cl}^-$$ * The resulting electrostatic attraction forms the ionic bond: $$\text{Na}^+ + \text{Cl}^- \rightarrow \text{NaCl}$$ #### 2. Covalent Bond Formed by the mutual sharing of valence electrons between non-metal atoms to achieve stable noble gas configurations. * **Single Covalent Bond:** Sharing of one electron pair, e.g., $\text{H}_2$ ($\text{H}-\text{H}$). * **Double Covalent Bond:** Sharing of two electron pairs, e.g., $\text{O}_2$ ($\text{O}=\text{O}$). * **Triple Covalent Bond:** Sharing of three electron pairs, e.g., $\text{N}_2$ ($\text{N}\equiv\text{N}$). ``` H . + . H ---> H : H (or H-H) Hydrogen Atoms Hydrogen Molecule ``` #### 3. Coordinate Covalent (Dative) Bond A special type of covalent bond where both the shared electrons are contributed by a single atom (the donor) to another atom (the acceptor). * **Example: Ammonium Ion ($\text{NH}_4^+$)** * Ammonia ($\text{NH}_3$) has a lone pair of electrons on the nitrogen atom. It donates this lone pair to an empty $1s$ orbital of an $\text{H}^+$ ion. $$\text{NH}_3 + \text{H}^+ \rightarrow [\text{NH}_3 \rightarrow \text{H}]^+ \text{ or } \text{NH}_4^+$$ #### 4. Metallic Bond The force of attraction that binds metal kernels (positive core of metal ions) to the mobile "sea of valence electrons" surrounding them. * **Example:** The cohesive forces keeping atoms bonded in solid copper ($\text{Cu}$) or iron ($\text{Fe}$). #### 5. Hydrogen Bond A weak electrostatic force of attraction between a hydrogen atom covalently bonded to a highly electronegative atom ($\text{F}$, $\text{O}$, or $\text{N}$) and another electronegative atom in the vicinity. * **Example: Water ($\text{H}_2\text{O}$)** $$\cdots \text{H}-\text{O} \cdots \text{H}-\text{O} \cdots \text{H}-\text{O} \cdots$$ --- --- ## Question 2 ### Q.2 (a) Define the following terms: Ionization Energy, Hard Acid, Covalent Bond [03 Marks] #### 1. Ionization Energy The minimum energy required to remove the most loosely bound electron from the outermost shell of an isolated, neutral gaseous atom in its ground state. $$\text{M}_{(g)} + \text{IE} \rightarrow \text{M}^+_{(g)} + e^-$$ #### 2. Hard Acid According to Pearson's HSAB (Hard and Soft Acids and Bases) principle, a hard acid is a Lewis acid that has a small ionic size, high positive oxidation state, and low polarizability (e.g., $\text{H}^+$, $\text{Na}^+$, $\text{Al}^{3+}$). #### 3. Covalent Bond A chemical bond formed by the mutual sharing of one or more pairs of electrons between two electronegative atoms (usually non-metals) to achieve a stable electronic configuration. --- ### Q.2 (b) Mention various sources and impurities present in water. [04 Marks] #### Sources of Water 1. **Surface Water:** Rainwater, rivers, lakes, streams, and reservoirs. 2. **Underground Water:** Springs and wells. #### Impurities in Water Water contains various physical, chemical, and biological impurities: ``` Impurities in Water | +-------------------------+-------------------------+ | | | Physical Impurities Chemical Impurities Biological Impurities - Suspended solids - Dissolved salts - Bacteria & viruses - Turbidity & clay - Dissolved gases - Algae & fungi - Color, odor, & taste - Organic matter - Pathogens ``` 1. **Physical Impurities:** * **Suspended matter:** Insoluble clay, sand, silt, and organic matter which make water turbid. * **Color, Odor, and Taste:** Caused by dissolved organic matter, industrial wastes, or dissolved gases. 2. **Chemical Impurities:** * **Dissolved Inorganic Salts:** Chlorides, sulfates, bicarbonates, and nitrates of calcium ($\text{Ca}^{2+}$), magnesium ($\text{Mg}^{2+}$), sodium ($\text{Na}^+$), and iron ($\text{Fe}^{2+}$). These salts cause hardness. * **Dissolved Gases:** $\text{O}_2, \text{CO}_2$, and $\text{H}_2\text{S}$ which lead to corrosion and unpleasant smells. 3. **Biological Impurities:** * Microorganisms like bacteria, viruses, protozoa, algae, and fungi, many of which are pathogens causing waterborne diseases. --- ### Q.2 (c) Explain various boiler problems & how can it be solved by engineering applications. [07 Marks] When hard water is fed into high-pressure boilers, it leads to several operating difficulties. #### 1. Scale and Sludge Formation * **Sludge:** A loose, slimy, and non-adherent precipitate formed in the colder parts of the boiler. It is caused by highly soluble salts like $\text{MgCO}_3, \text{MgCl}_2$, and $\text{MgSO}_4$. * **Scale:** A hard, dense, and strongly adherent crust formed on the inner walls of the boiler. It is caused by salts like $\text{CaSO}_4$, $\text{Ca(HCO}_3)_2$ (which decomposes to $\text{CaCO}_3$), and silica ($\text{SiO}_2$). * **Engineering Solutions:** * **Blow-down operation:** Regularly releasing a portion of concentrated boiler water to remove loose sludge. * **Internal conditioning:** Adding chemicals to convert scale-forming precipitates into soft sludges: * *Phosphate conditioning:* Adding sodium phosphate to precipitate calcium as soft calcium phosphate. * *Calgon conditioning:* Adding Calgon (sodium hexametaphosphate) to form a highly soluble complex with calcium ions. #### 2. Boiler Corrosion Chemical decay of the boiler's metallic surface due to reactions with the water or dissolved gases. * **Causes:** Dissolved oxygen, dissolved $\text{CO}_2$, or acids produced by the hydrolysis of salts (e.g., $\text{MgCl}_2 + 2\text{H}_2\text{O} \rightarrow \text{Mg(OH)}_2 + 2\text{HCl}$). * **Engineering Solutions:** * **Chemical de-aeration:** Adding reducing agents like sodium sulfite ($\text{Na}_2\text{SO}_3$) or hydrazine ($\text{N}_2\text{H}_4$) to scavenge dissolved oxygen: $$\text{N}_2\text{H}_4 + \text{O}_2 \rightarrow \text{N}_2 + 2\text{H}_2\text{O}$$ * **Mechanical de-aeration:** Spraying water over heated metal plates in a vacuum column to remove dissolved gases. #### 3. Priming and Foaming (Carry-over) * **Priming:** The rapid, violent boiling of water where small droplets of liquid water are carried into the steam pipes along with the steam. * **Foaming:** The formation of stable, persistent bubbles on the surface of boiler water that do not break easily, caused by high concentrations of oils, fats, and organic matter. * **Engineering Solutions:** * Maintaining low water levels in the boiler. * Installing mechanical steam purifiers and separators. * Adding anti-foaming agents like castor oil. #### 4. Caustic Embrittlement A type of stress corrosion cracking that occurs in high-pressure boilers, specifically at riveted joints and bends, where highly alkaline water containing sodium hydroxide ($\text{NaOH}$) concentrates and attacks the steel. $$\text{Fe} + 2\text{NaOH} \rightarrow \text{Na}_2\text{FeO}_2 + \text{H}_2$$ * **Engineering Solutions:** * Using sodium phosphate ($\text{Na}_3\text{PO}_4$) instead of sodium carbonate ($\text{Na}_2\text{CO}_3$) as a softening agent to avoid the formation of $\text{NaOH}$. * Adding tannins, lignins, or sodium sulfate ($\text{Na}_2\text{SO}_4$) to block the microscopic cracks and prevent concentration of $\text{NaOH}$ on the metal surface. --- ### OR (c) Explain various softening methods with suitable diagrams. [07 Marks] Water softening is the process of removing the dissolved calcium and magnesium salts that cause water hardness. The two most common modern industrial methods are the **Zeolite Process** and the **Ion-Exchange Process**. #### 1. Zeolite (Permutit) Process Zeolites are hydrated sodium aluminosilicates ($\text{Na}_2\text{O} \cdot \text{Al}_2\text{O}_3 \cdot x\text{SiO}_2 \cdot y\text{H}_2\text{O}$), represented simply as $\text{Na}_2\text{Ze}$. They have the unique property of exchanging their sodium ions for hardness-causing calcium and magnesium ions. ##### Mechanism Hard water is passed through a bed of zeolite. The calcium and magnesium ions are captured by the zeolite, and sodium ions are released into the water. $$\text{Ca(HCO}_3)_2 + \text{Na}_2\text{Ze} \rightarrow \text{CaZe} + 2\text{NaHCO}_3$$ $$\text{MgSO}_4 + \text{Na}_2\text{Ze} \rightarrow \text{MgZe} + \text{Na}_2\text{SO}_4$$ ##### Regeneration When the zeolite bed gets exhausted, it is regenerated by washing it with a $10\%$ brine ($\text{NaCl}$) solution. $$\text{CaZe} + 2\text{NaCl} \rightarrow \text{Na}_2\text{Ze} + \text{CaCl}_2 \text{ (washed out)}$$ ``` Zeolite Softener Diagram +------------------------------+ Hard Water | | ------------> | ================= | | / \ | | | Zeolite Bed | | <--- Brine (NaCl) Inlet | \ / | | ================= | | | +--------------+---------------+ | v Soft Water ``` --- #### 2. Ion-Exchange (Demineralization) Process This process completely removes all cations and anions from water, producing pure demineralized (deionized) water. It uses two columns filled with synthetic organic resins: ##### A. Cation-Exchange Column Contains acidic resins ($\text{RH}^+$) that exchange hydrogen ions ($\text{H}^+$) for cations like $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, and $\text{Na}^+$. $$2\text{RH}^+ + \text{Ca}^{2+} \rightarrow \text{R}_2\text{Ca}^{2+} + 2\text{H}^+$$ * **Regeneration:** The exhausted resin is treated with dilute $\text{HCl}$ or $\text{H}_2\text{SO}_4$. ##### B. Anion-Exchange Column Contains basic resins ($\text{ROH}^-$) that exchange hydroxyl ions ($\text{OH}^-$) for anions like $\text{Cl}^-$, $\text{SO}_4^{2-}$, and $\text{HCO}_3^-$. $$\text{ROH}^- + \text{Cl}^- \rightarrow \text{RCl}^- + \text{OH}^-$$ * **Regeneration:** The exhausted resin is treated with dilute $\text{NaOH}$ solution. * **Neutralization:** The released $\text{H}^+$ and $\text{OH}^-$ ions combine to form water: $$\text{H}^+ + \text{OH}^- \rightarrow \text{H}_2\text{O}$$ ``` Ion-Exchange Softening Unit +------------+ +------------+ Hard Water -> | Cation | ---> | Anion | -> Demineralized | Exchange | | Exchange | Water | Resin | | Resin | +------------+ +------------+ ``` --- --- ## Question 3 ### Q.3 (a) Define the following terms: Soft Water, Brine, Coagulant [03 Marks] #### 1. Soft Water Water that contains very low concentrations of dissolved calcium and magnesium ions, meaning it readily forms a rich lather with soap. #### 2. Brine A highly concentrated solution of sodium chloride ($\text{NaCl}$) in water, typically with a salt concentration of around $10\%$ to $20\%$. It is commonly used for regenerating zeolite and ion-exchange units. #### 3. Coagulant A chemical substance (such as alum or ferrous sulfate) added to water to neutralize the negative electrical charges on fine, suspended colloidal particles, encouraging them to clump together into larger, easily filterable aggregates called flocs. --- ### Q.3 (b) Mention various properties of metals with examples. [04 Marks] Metals are electropositive elements characterized by unique physical and chemical properties: #### 1. Physical Properties * **Malleability:** The ability to be beaten or hammered into extremely thin sheets without cracking. * *Example:* Gold ($\text{Au}$) and Aluminium ($\text{Al}$) foils. * **Ductility:** The capability of being drawn into thin, fine wires. * *Example:* Copper ($\text{Cu}$) and Tungsten ($\text{W}$). * **Electrical and Thermal Conductivity:** High conductivity due to the presence of free, mobile valence electrons. * *Example:* Silver ($\text{Ag}$) and Copper ($\text{Cu}$). * **Luster:** A shiny, reflective surface appearance when freshly cut. * *Example:* Platinum ($\text{Pt}$) and Chromium ($\text{Cr}$). #### 2. Chemical Properties * **Electropositive Nature:** Metals easily lose valence electrons to form stable cations. * *Example:* Sodium ($\text{Na} \rightarrow \text{Na}^+ + e^-$). * **Formation of Basic Oxides:** When heated with oxygen, metals form basic oxides. * *Example:* Magnesium ($2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$). --- ### Q.3 (c) Explain domestic water treatment and also desalination of brackish water. [07 Marks] #### 1. Domestic Water Treatment (Municipal Water Treatment) The process of treating raw surface water to make it safe, clean, and potable (suitable for drinking). ``` Raw Water -> [ Screening ] -> [ Sedimentation ] -> [ Coagulation ] -> [ Filtration ] -> [ Disinfection ] -> Potable Water ``` 1. **Screening:** Water is passed through large metal screens to remove large floating materials like leaves, branches, wood, and plastic. 2. **Plain Sedimentation:** Water is stored in large basins to allow heavy suspended sand, clay, and silt particles to settle out under gravity. 3. **Coagulation:** For fine colloidal particles that do not settle easily, coagulants like alum $[\text{Al}_2(\text{SO}_4)_3]$ are added. This forms a gelatinous precipitate of $\text{Al(OH)}_3$ which traps and carries down the fine colloidal particles. 4. **Filtration:** The clear water is passed through rapid/slow sand filters to remove residual suspended matter, micro-particles, and some bacteria. 5. **Disinfection (Sterilization):** Pathogenic bacteria are killed to prevent waterborne diseases. This is achieved using: * **Chlorination:** Adding liquid chlorine or bleaching powder, which forms hypochlorous acid ($\text{HOCl}$), a powerful disinfectant. * **Ozonization:** Using ozone ($\text{O}_3$), which acts as a powerful oxidant. * **UV Radiation:** Exposing water to ultraviolet light. --- #### 2. Desalination of Brackish Water Brackish water contains high concentrations of dissolved salts (salinity between $1,500$ to $35,000$ ppm). It is converted into fresh, potable water using **Reverse Osmosis (RO)**. ``` Reverse Osmosis (RO) Process Applied Pressure (> Osmotic Pressure) | v +---------------+---------------+ | Salt Water | Pure Water | | (Brackish) | | | | | +---------------+---------------+ ^ Semi-Permeable Membrane (SPM) ``` ##### Principle of Reverse Osmosis When two solutions of different concentrations are separated by a semi-permeable membrane, water naturally flows from the dilute side to the concentrated side (osmosis). If a hydrostatic pressure greater than the osmotic pressure is applied to the concentrated (saltwater) side, the direction of flow is reversed. Pure water is forced from the salt-rich side through the semi-permeable membrane to the freshwater side, leaving the salts behind. ##### Features * **Membrane material:** Thin-film composite membranes made of Cellulose Acetate, Polyamides, or Polysulfone. * **Advantages:** Extremely high efficiency, low energy requirements compared to thermal distillation, and simultaneous removal of ionic, organic, and biological contaminants. --- --- ### OR Q.3 (a) Define the following terms: Metals, Non-Metals, Alloy [03 Marks] #### 1. Metals Elements that are characterized by being electropositive, lustrous, malleable, ductile, and excellent conductors of electricity and heat (e.g., $\text{Fe}, \text{Al}, \text{Cu}$). #### 2. Non-Metals Elements that are highly electronegative, brittle in their solid state, non-lustrous, and poor conductors of heat and electricity (e.g., $\text{C}, \text{O}_2, \text{S}$). #### 3. Alloy A homogeneous, intimate mixture of two or more metals, or a metal and a non-metal, prepared by fusing them together to improve physical and mechanical characteristics (e.g., Brass, Steel). --- ### OR Q.3 (b) What are alloys, classify them with examples? [04 Marks] An **alloy** is an intimate, homogeneous metallic mixture composed of two or more chemical elements, of which at least one is a metal. ``` Alloys | +---------------------+---------------------+ | | Ferrous Alloys Non-Ferrous Alloys - Contain Iron - Do not contain Iron - Examples: Steel, Stainless Steel - Examples: Brass, Bronze ``` #### Classification of Alloys ##### 1. Based on the Presence of Iron (Fe) * **Ferrous Alloys:** Alloys where iron ($\text{Fe}$) is the major, primary constituent element. * *Example:* **Carbon Steel** ($\text{Fe} + \text{C}$), **Stainless Steel** ($\text{Fe} + \text{Cr} + \text{Ni} + \text{C}$). * **Non-Ferrous Alloys:** Alloys that do not contain iron as the principal constituent. * *Example:* **Brass** ($\text{Cu} + \text{Zn}$), **Bronze** ($\text{Cu} + \text{Sn}$), **Duralumin** ($\text{Al} + \text{Cu} + \text{Mg} + \text{Mn}$). ##### 2. Based on Phase and Microstructure * **Homogeneous Alloys (Solid Solutions):** A single-phase alloy where the solute atoms are distributed within the solvent metal lattice (e.g., Brass). * **Heterogeneous Alloys:** Multi-phase systems containing distinct microscopic phases (e.g., Lead-Tin solder). --- ### OR Q.3 (c) Explain the metallurgy of copper with industrial applications. [07 Marks] The commercial extraction of copper from its primary sulfide ore, **Copper Pyrites ($\text{CuFeS}_2$)**, involves several key steps: ``` Ore Extraction -> Crushing -> Froth Flotation -> Roasting -> Smelting -> Bessemerization -> Refining (99.9% Cu) ``` #### Extraction Steps ##### 1. Crushing and Grinding The mined lump ore is crushed in jaw crushers and then pulverized to a fine powder in ball mills. ##### 2. Concentration (Froth Flotation) The powdered ore is mixed with water, pine oil, and xanthates in a flotation tank. Air is blown through the mixture. The copper sulfide particles attach to the oil-coated air bubbles and rise to the surface as a froth, while the silicate gangue (impurities) sinks to the bottom. ##### 3. Roasting The concentrated ore is heated in a reverberatory furnace in the presence of air. Volatile impurities like arsenic ($\text{As}$), sulfur ($\text{S}$), and antimony ($\text{Sb}$) escape as oxides. $$2\text{CuFeS}_2 + \text{O}_2 \rightarrow \text{Cu}_2\text{S} + 2\text{FeS} + \text{SO}_2 \uparrow$$ ##### 4. Smelting The roasted ore is mixed with coke and sand ($\text{SiO}_2$) and heated in a blast furnace. Iron sulfide ($\text{FeS}$) oxidizes to ferrous oxide ($\text{FeO}$), which reacts with sand to form an easily removable liquid slag ($\text{FeSiO}_3$). $$2\text{FeS} + 3\text{O}_2 \rightarrow 2\text{FeO} + 2\text{SO}_2 \uparrow$$ $$\text{FeO} + \text{SiO}_2 \rightarrow \text{FeSiO}_3 \text{ (Slag)}$$ The remaining molten material is called **Copper Matte** (a mixture of $\text{Cu}_2\text{S}$ and some remaining $\text{FeS}$). ##### 5. Bessemerization Molten copper matte is transferred into a pear-shaped Bessemer converter, and air is blown through it along with sand. The remaining iron is converted into slag. The copper sulfide undergo self-reduction to produce copper metal: $$2\text{Cu}_2\text{S} + 3\text{O}_2 \rightarrow 2\text{Cu}_2\text{O} + 2\text{SO}_2 \uparrow$$ $$2\text{Cu}_2\text{O} + \text{Cu}_2\text{S} \rightarrow 6\text{Cu} + \text{SO}_2 \uparrow$$ The escaping bubbles of sulfur dioxide ($\text{SO}_2$) give the cooled solid metal a blistered surface. This product is called **Blister Copper** (about $98\%$ pure). ##### 6. Electrolytic Refining To make it suitable for electrical use, blister copper is refined. Anode blocks of blister copper and cathode sheets of pure copper are immersed in an acidic solution of copper sulfate ($\text{CuSO}_4$). On passing electric current, pure copper ($99.9\%$) deposits on the cathode. #### Industrial Applications of Copper * **Electrical Industry:** Because of its high electrical conductivity, it is the primary metal used for manufacturing electrical transmission wires, cables, electromagnets, and printed circuit boards (PCBs). * **Heat Exchangers:** Used in radiators, condensers, and boilers because of its high thermal conductivity and resistance to corrosion. * **Alloy Manufacture:** Widely used to produce industrial alloys like brass, bronze, and cupronickel. --- --- ## Question 4 ### Q.4 (a) Define the following terms: Polymers, Fibers, Rubber [03 Marks] #### 1. Polymers High molecular weight macromolecules formed by linking together a large number of small, repeating structural units called monomers via covalent chemical bonds. #### 2. Fibers A class of polymers characterized by high tensile strength, low elasticity, and strong intermolecular forces (such as hydrogen bonding) that allow them to be drawn into thin, long, thread-like structures. #### 3. Rubber (Elastomers) A class of linear polymers that possess high elasticity and low intermolecular attractive forces. They can be stretched to several times their original length under tension and return to their original shape when the stress is released. --- ### Q.4 (b) Mention different types of rubber and why it is vulcanized? [04 Marks] #### Types of Rubber 1. **Natural Rubber:** A polymer of isoprene (cis-1,4-polyisoprene) harvested from the latex of the *Hevea brasiliensis* tree. 2. **Synthetic Rubber:** Industrially manufactured elastomers designed to withstand harsh environments (e.g., **Neoprene**, **Buna-S**, **Buna-N**, and **Butyl rubber**). #### Why Rubber is Vulcanized Raw natural rubber has several undesirable properties: * It is soft and sticky when hot, and brittle when cold. * It has low tensile strength and poor wear resistance. * It absorbs large quantities of water and is easily dissolved by organic solvents. ##### The Vulcanization Process Vulcanization is the process of heating raw rubber with $1\%$ to $5\%$ sulfur at $100^\circ\text{C}$ to $140^\circ\text{C}$. This chemical process introduces cross-linking sulfur bridges between adjacent polymer chains. ``` Raw Rubber (Linear Chains) Vulcanized Rubber (Cross-linked) ==================== ==================== | | | | ==================== ====S===S===S===S=== | | | | ==================== ==================== ``` ##### Properties Improved by Vulcanization * **Elasticity & Strength:** The cross-linked structure prevents the chains from slipping past each other permanently, improving tensile strength and elasticity. * **Temperature Stability:** It remains resilient across a much wider temperature range. * **Solvent Resistance:** It becomes highly resistant to swelling, degradation, and dissolution by organic solvents and oils. --- ### Q.4 (c) Classify in detail fibers along with their importance to society. [07 Marks] Fibers can be systematically classified based on their origin and source: ``` Fibers | +----------------------------+----------------------------+ | | | Natural Fibers Semi-Synthetic Fibers Synthetic Fibers - Cotton, Wool, Silk - Rayon - Nylon, Polyester ``` #### 1. Detailed Classification ##### A. Natural Fibers Directly obtained from plants, animals, or minerals: * **Plant-Based (Cellulosic):** Made primarily of cellulose. * *Examples:* Cotton, Jute, Flax, Hemp. * **Animal-Based (Protein):** Composed of complex proteins. * *Examples:* Wool (from sheep/goats), Silk (from silkworms). * **Mineral-Based:** Naturally occurring mineral fibers. * *Example:* Asbestos. ##### B. Semi-Synthetic (Regenerated) Fibers Derived from natural cellulose that is chemically processed, dissolved, and extruded to reform new fibers. * *Example:* **Rayon** (Viscose), Cellulose Acetate. ##### C. Synthetic (Man-Made) Fibers Completely synthesized in factories from chemical petrochemical precursors through polymerization: * **Polyamides:** Nylon 6,6 and Nylon 6. * **Polyesters:** Terylene (Dacron). * **Acrylics:** Orlon. --- #### 2. Importance of Fibers to Society * **Apparel and Fashion:** Fibers are woven into textiles to produce clothing that provides comfort, style, and protection from the weather. * **Industrial and Structural Applications:** High-strength synthetic fibers like **Kevlar** are used in bulletproof vests, helmets, and radial tires. Nylon is used to manufacture seatbelts, climbing ropes, and parachutes. * **Medical Fields:** Synthetic biodegradable fibers are used as surgical sutures, vascular grafts, artificial skin, and filtration materials in face masks. * **Home Furnishings:** Essential for making carpets, ropes, insulation mats, bed sheets, and upholstery. --- --- ### OR Q.4 (a) Define the following terms: Nano Material, Fuel, Catalyst [03 Marks] #### 1. Nano Material Materials that have structured features with at least one dimension in the nanoscale size range of $1$ to $100$ nanometers ($1 \text{ nm} = 10^{-9} \text{ m}$). #### 2. Fuel Any combustible, carbonaceous substance that releases large quantities of heat energy through rapid chemical oxidation (combustion) that can be utilized economically for industrial or domestic heating purposes. #### 3. Catalyst A chemical substance that increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy, without undergoing any permanent chemical change itself. --- ### OR Q.4 (b) What are the sources, properties and applications of fullerenes? [04 Marks] Fullerenes are an allotrope of carbon where carbon atoms are linked in a hollow cage-like configuration. The most common and stable form is **Buckminsterfullerene ($C_{60}$)**, which consists of $20$ hexagons and $12$ pentagons structured like a soccer ball. ``` C60 Fullerene Structure (Truncated Icosahedron) ``` #### Sources of Fullerenes * Prepared in laboratories by vaporizing high-purity graphite rods in an electric arc under an inert helium atmosphere. * Found naturally in tiny amounts in soot from wood combustion and certain ancient carbonaceous rocks (shungite). #### Properties * **Structure:** Hollow, cage-like structure that is highly stable and resistant to extreme temperature and high pressure. * **Chemical Nature:** Highly electronegative; it acts as an electron acceptor and can easily undergo addition reactions. * **Electrical Behavior:** Pure fullerenes are semiconductors, but when doped with alkali metals (e.g., $K_3C_{60}$), they become superconductors at low temperatures. #### Applications * **Medical Field:** Used as targeted drug-delivery systems because their hollow cages can encapsulate drugs, and as powerful antioxidants to scavenge free radicals. * **Photovoltaics & Electronics:** Used as organic electron acceptors in modern solar panels and thin-film transistors. * **Industrial Lubricants:** Their spherical geometry allows them to behave like molecular ball bearings, reducing friction. --- ### OR Q.4 (c) Explain application of nano materials in catalysts, textile and medicine. [07 Marks] Because of their high surface-area-to-volume ratio, nanomaterials exhibit unique physical and chemical properties that differ from bulk materials. #### 1. Applications in Catalysts (Nanocatalysis) * **High Efficiency:** Decreasing the catalyst particle size down to the nanoscale increases the exposed surface area. This significantly increases the number of active catalytic sites per unit mass. * **Vehicle Exhaust Systems:** Precious metal nanoparticles (such as Platinum, Palladium, and Rhodium) are used in automotive catalytic converters to reduce toxic emissions ($\text{CO}$ to $\text{CO}_2$, $\text{NO}_x$ to $\text{N}_2$). * **Industrial Chemistry:** Nickel and Gold nanoparticles are used to catalyze organic hydrogenation and selective oxidation reactions at lower operating temperatures. #### 2. Applications in Textiles (Smart Fabrics) * **Water and Stain Repellency:** Coating fabrics with silica ($\text{SiO}_2$) or titanium dioxide ($\text{TiO}_2$) nanoparticles creates a microscopic rough structure. This structure repels water and oil, mimicking the self-cleaning "lotus effect." * **Antimicrobial and Anti-odor Clothing:** Embedding Silver nanoparticles ($\text{Ag-NPs}$) into fibers releases $\text{Ag}^+$ ions that destroy bacterial cell walls. This prevents bacterial growth and odor in activewear. * **UV Protection:** Incorporating zinc oxide ($\text{ZnO}$) or titanium dioxide ($\text{TiO}_2$) nanoparticles into clothing blocks ultraviolet radiation, protecting the skin. #### 3. Applications in Medicine (Nanomedicine) * **Targeted Drug Delivery:** Nanoparticles like liposomes, dendrimers, and gold nanoparticles can encapsulate therapeutic drugs. They can target cancer tumors directly by utilizing specific surface ligands, minimizing side effects on healthy tissues. * **Advanced Diagnostics and Imaging:** Quantum dots (fluorescent semiconductor nanocrystals) and magnetic iron oxide nanoparticles are used to enhance contrast in MRI scans, helping to detect cancers at a very early stage. * **Wound Healing:** Silver nanoparticle gels are used in burn dressings to prevent wound infections and accelerate skin regeneration. --- --- ## Question 5 ### Q.5 (a) Define the following terms: Combustion, Biotechnology, Enzyme [03 Marks] #### 1. Combustion A rapid, high-temperature exothermic chemical reaction between a fuel substance and an oxidant (usually atmospheric oxygen) that releases heat, light, and gaseous combustion products. #### 2. Biotechnology The industrial application of living organisms, biological systems, or cellular components to develop, modify, or manufacture products for human welfare, medicine, and agriculture. #### 3. Enzyme A biological catalyst, typically a complex protein molecule produced by living cells, that accelerates biochemical reactions with high specificity and efficiency under mild conditions of temperature and pH. --- ### Q.5 (b) What is fractional distillation? [04 Marks] Fractional distillation is a chemical separation process used to separate a mixture of two or more miscible, volatile liquids with boiling points that are close to each other (typically with a difference of less than $25^\circ\text{C}$). ``` Fractional Distillation Column [ Condenser ] ===> Liquid Fraction ^ | (Vapors of lower boiling component) +-----------------+ | Fractionating | | Column | <--- Repeated vaporization | (Glass beads / | and condensation cycles | trays) | +-----------------+ ^ | [ Boiling Flask ] (Liquid Mixture) ``` #### Principle The separation relies on the difference in volatility of the components. When the mixture is heated, the vapors produced contain a higher concentration of the more volatile (lower boiling point) component. As these vapors rise through a **fractionating column** (filled with glass beads or plates), they undergo repeated cycles of condensation and re-vaporization. With each cycle, the vapor becomes richer in the more volatile component, which eventually reaches the top of the column, condenses, and is collected as a pure liquid. The less volatile component condenses and falls back into the distilling flask. #### Industrial Example * The refining of crude petroleum in oil refineries into useful fractions like gasoline, diesel, kerosene, and lubricating oils. --- ### Q.5 (c) What is proximate analysis for coal? [07 Marks] Proximate analysis is an empirical, rapid analytical testing method used to assess the quality and commercial value of a coal sample. It determines the percentages of four main components: **Moisture, Volatile Matter, Ash, and Fixed Carbon**. #### 1. Moisture Content (M) * **Procedure:** $1 \text{ g}$ of finely powdered, air-dried coal is heated in a silica crucible in an oven at $105^\circ\text{C}$ to $110^\circ\text{C}$ for $1$ hour. It is then cooled and weighed. * **Calculation:** $$\% \text{ Moisture} = \frac{\text{Loss in weight of coal}}{\text{Initial weight of coal taken}} \times 100$$ * **Significance:** High moisture reduces the calorific value of the coal because it consumes heat to evaporate. Therefore, low moisture content is preferred. #### 2. Volatile Matter (VM) * **Procedure:** The moisture-free coal sample from the first step is placed in a covered crucible and heated in a muffle furnace at $950 \pm 20^\circ\text{C}$ for exactly $7$ minutes. * **Calculation:** $$\% \text{ Volatile Matter} = \frac{\text{Loss in weight due to removal of VM}}{\text{Initial weight of coal taken}} \times 100$$ * **Significance:** High volatile matter content causes coal to burn with a long, smoky flame, reducing heating efficiency and increasing air pollution. Therefore, low volatile matter is preferred. #### 3. Ash Content (A) * **Procedure:** The residue left in the crucible after removing moisture and volatile matter is heated in an open crucible (allowing air access) at $700^\circ\text{C}$ to $750^\circ\text{C}$ until all carbonaceous matter is completely burnt away. * **Calculation:** $$\% \text{ Ash} = \frac{\text{Weight of residue left (ash)}}{\text{Initial weight of coal taken}} \times 100$$ * **Significance:** Ash is the non-combustible inorganic residue. High ash content reduces the heating value, makes handling and disposal difficult, and can clog the furnace grates. Low ash content is preferred. #### 4. Fixed Carbon (FC) * **Procedure:** This is determined by subtracting the sum of the percentages of moisture, volatile matter, and ash from $100$. * **Calculation:** $$\% \text{ Fixed Carbon} = 100 - [\% \text{ Moisture} + \% \text{ Volatile Matter} + \% \text{ Ash}]$$ * **Significance:** Fixed carbon represents the main combustible material in coal. High fixed carbon is highly desirable because it directly increases the calorific value of the coal. --- --- ### OR Q.5 (a) Define the following terms: pH, Spectra, Conductance [03 Marks] #### 1. pH The negative logarithm (to base 10) of the hydrogen ion ($\text{H}^+$) activity or concentration in an aqueous solution. It indicates the acidity or alkalinity of a solution. $$\text{pH} = -\log_{10}[\text{H}^+]$$ #### 2. Spectra (Spectrum) A graphical chart or pattern of electromagnetic radiation emitted, absorbed, or scattered by a substance, plotted as a function of wavelength, frequency, or wavenumber. #### 3. Conductance The measure of the ease with which electrical current flows through an electrical conductor or electrolyte solution. It is the reciprocal of electrical resistance ($R$). $$G = \frac{1}{R} \quad (\text{Unit: Siemens or }\Omega^{-1})$$ --- ### OR Q.5 (b) How is biotechnology helpful in agriculture, food and in medicine? [04 Marks] #### 1. In Agriculture * **Genetically Modified (GM) Crops:** Development of pest-resistant crop varieties, such as **Bt Cotton**, which contain genes from *Bacillus thuringiensis* to resist insects, reducing the need for chemical pesticides. * **Environmental Tolerance:** Breeding drought-resistant, frost-resistant, and salt-tolerant crops. * **Biofertilizers:** Using nitrogen-fixing bacteria (like *Rhizobium*) to naturally enrich soil quality. #### 2. In the Food Industry * **Fermentation Products:** Utilizing specialized yeast and bacterial strains to produce bread, cheese, yogurt, wine, and beer. * **Nutritional Enhancement:** Engineering staple foods to contain higher nutrient concentrations, such as **Golden Rice**, which is enriched with Vitamin A. * **Enzymes:** Using enzymes like amylase and pectinase for fruit juice clarification and baking. #### 3. In Medicine * **Recombinant Hormones:** Mass production of human insulin (**Humulin**) using genetically engineered *E. coli* bacteria. * **Vaccines:** Developing modern recombinant subunit vaccines and mRNA vaccines (such as those used for COVID-19). * **Gene Therapy:** Inserting functional genes to correct genetic mutations and treat hereditary disorders. --- ### OR Q.5 (c) Mention the principles of spectroscopy along with their application. [07 Marks] Spectroscopy is the study of how electromagnetic radiation (EMR) interacts with matter (atoms, ions, or molecules). #### General Operating Principle When a sample is exposed to electromagnetic radiation, it can absorb, emit, or scatter specific wavelengths. This interaction induces transitions between quantized energy states of the atoms or molecules. The energy difference ($\Delta E$) is directly proportional to the frequency ($\nu$) of the absorbed or emitted radiation: $$\Delta E = h\nu = \frac{hc}{\lambda}$$ Where: * $h = \text{Planck's constant}$ * $c = \text{speed of light}$ * $\lambda = \text{wavelength}$ --- #### Major Spectroscopic Techniques | Spectroscopy Type | Key Principle | Major Industrial/Lab Applications | | :--- | :--- | :--- | | **1. UV-Visible Spectroscopy** | **Electronic Transitions:** Absorption of light in the UV ($200\text{-}400 \text{ nm}$) or Visible ($400\text{-}800 \text{ nm}$) region promotes valence electrons to higher energy molecular orbitals. Follows the **Beer-Lambert Law**: $$A = \epsilon c l$$ | * Quantitative analysis of colored metal complexes and organic drugs.
* Determining concentrations of solutions. | | **2. Infrared (IR) Spectroscopy** | **Molecular Vibrations:** Absorption of infrared radiation ($4000\text{-}400 \text{ cm}^{-1}$) changes the dipole moment of a molecule, inducing vibrational stretching and bending. | * Identification of organic functional groups (e.g., $-\text{OH}$ stretch, $-\text{C=O}$ stretch).
* "Fingerprinting" chemical structures. | | **3. Nuclear Magnetic Resonance (NMR)** | **Nuclear Spin Transitions:** Uses radiofrequency waves in a strong magnetic field to change the spin states of active nuclei (such as $^1\text{H}$ or $^{13}\text{C}$). | * Structural determination of complex organic molecules and synthetic polymers.
* Used as Magnetic Resonance Imaging (MRI) in clinical medicine. | | **4. Flame Photometry** | **Atomic Emission:** Exposing a sample to a flame thermalizes metal atoms, exciting their electrons. As they return to the ground state, they emit light at characteristic wavelengths. | * Estimating the concentration of alkali and alkaline-earth metals (like $\text{Na}^+, \text{K}^+, \text{Ca}^{2+}$) in soil and biological fluids. |