GTU 3110001 Chemistry Summer 2023 Solved Paper & Solutions

• Definition: Priming is the violent, rapid boiling of boiler water, causing liquid water droplets to be carried along mechanically with the outgoing steam into the steam line (producing "wet steam").
• Causes:

1. High boiler water level.
2. Extremely high steam withdrawal velocity.
3. Sudden steam demand variations.
4. Improper boiler design lacking adequate steam space.

• Prevention:
• Maintain optimal water levels.
• Avoid sudden steam production spikes.
• Install steam purifiers and separators.

• Definition: Foaming is the formation of persistent, stable bubbles or foam on the surface of boiler water that does not easily break, rising into the steam pipe.
• Causes:
• Presence of dissolved oily, fatty, soapy substances or high concentrations of suspended organic solids and alkalis ($NaOH$) that lower the surface tension of water.
• Disadvantages of Priming & Foaming (Carry-Over):
• Dissolved boiler salts enter steam turbines and superheaters, forming corrosive deposits and causing mechanical water-hammer damage.
• Prevention of Foaming:
• Add anti-foaming agents like Castor Oil or synthetic polyamides.
• Blow-down boiler water periodically to discharge accumulated dissolved solids.

Electrochemical corrosion occurs when a metal comes into contact with a conducting aqueous electrolyte. Galvanic micro-cells (anodic and cathodic regions) are set up on the metal surface:

Cathodic protection forces the entire metal structure to behave as a cathode, preventing oxidation:

Proximate analysis is a standardized experimental method (ASTM D3172) used to assess the commercial quality of coal by determining the percentages of Moisture, Volatile Matter, Ash, and Fixed Carbon.

• High moisture and ash reduce calorific value and increase shipping cost. High fixed carbon denotes premium high-rank coal (Anthracite).

Refining separates crude petroleum oil into commercially useful fractions based on their boiling point ranges in a tall fractionating column.

• Vapors ascend bubble-cap trays; heavier components with higher boiling points condense near the bottom, while lighter fractions with lower boiling points condense higher up.

1. High Calorific Value: Produces maximum heat per unit mass.
2. Moderate Ignition Temperature: Not too low (safety hazard) and not too high (difficult to ignite).
3. Low Moisture & Ash Content: Moisture absorbs heat; ash reduces heating value and clinkers grates.
4. Harmless Combustion Byproducts: Free from toxic and corrosive gases ($SO_2, H_2S, CO$).
5. Controllable Combustion Rate: Clean and steady combustion without explosion.
6. Economical & Easy Transport: Cheap, readily available, safe storage.

• Definition: Measures the anti-knocking capability of petrol in spark-ignition (SI) internal combustion engines.
• Standard Scale:
• Iso-octane ($2,2,4$-trimethylpentane): Excellent anti-knocking properties $\implies \text{Octane Number} = 100$.
• n-Heptane: Severe knocking $\implies \text{Octane Number} = 0$.
• Octane Number is the percentage by volume of iso-octane in a mixture with n-heptane that matches the knocking of the test fuel.

• Definition: Measures the ignition delay of diesel fuel in compression-ignition (CI) diesel engines.
• Standard Scale:
• Cetane (n-hexadecane): Short ignition delay $\implies \text{Cetane Number} = 100$.
• $\alpha$-Methylnaphthalene: Long ignition delay $\implies \text{Cetane Number} = 0$.
• Higher Cetane number means faster ignition, smoother cold starts, and minimal engine knock.

• Lambert's Law: When a monochromatic light beam passes through a homogeneous absorbing medium, the rate of decrease of intensity with the path length (thickness) of the medium is directly proportional to the incident light intensity.

• Beer's Law: The rate of decrease of light intensity with path length is directly proportional to both the incident light intensity and the molar concentration of the absorbing solute.

• Combining both laws:

• Integrating between limits: when $x = 0$, $I = I_0$ (incident intensity); when $x = l$, $I = I_t$ (transmitted intensity):

• Converting to base-10 logarithm ($\\log_{10}$):

• Define Molar Absorptivity / Extinction Coefficient $\epsilon = \frac{k}{2.303}$, and Absorbance $A = \log_{10}\left(\frac{I_0}{I_t}\right)$:

where $c$ = concentration (mol/L), and $l$ = path length of cuvette (cm).

Fermentation is an anaerobic, bio-chemical metabolic process in which microorganisms (such as yeast or bacteria) enzymatically convert complex carbohydrates (sugars, starches) into simpler organic compounds like alcohols or organic acids, releasing carbon dioxide.

• Raw Material: Molasses (a byproduct of sugar mills containing $\approx 50\%$ fermentable sugars like sucrose, glucose, and fructose).

1. Dilution: Molasses is diluted with water to a sugar concentration of $10 - 15\%$.
2. Acidification: Diluted mash is acidified to $pH \approx 4.0 - 4.5$ using dilute $H_2SO_4$ to inhibit pathogenic bacterial growth and favor yeast growth.
3. Nutrient Addition: Ammonium sulfate or phosphate is added to nourish yeast cells.
4. Inoculation & Fermentation: Yeast (Saccharomyces cerevisiae) is added at $25^\circ\text{C} - 30^\circ\text{C}$. Yeast secretes two vital enzymes:

• Invertase: Hydrolyzes sucrose into glucose and fructose:

• Zymase: Converts glucose/fructose into ethanol and carbon dioxide:

5. Fractional Distillation: Fermentation completes in 2–3 days yielding "wash" ($8 - 10\%$ alcohol). Fractional distillation yields Rectified Spirit ($95.6\%$ ethanol).

1. Extremely High Specific Surface-to-Volume Ratio:

• As particle size decreases to the nanoscale ($1 - 100\ \text{nm}$), the percentage of surface atoms with uncoordinated active sites skyrockets, multiplying catalytic reaction rates.

2. Industrial Applications:

• Platinum ($Pt$) & Palladium ($Pd$) Nanoparticles: Used in automotive catalytic converters to convert toxic $CO$ and $NO_x$ emissions into harmless $CO_2$ and $N_2$.
• Gold ($Au$) Nanoparticles: Highly active for room-temperature oxidation of carbon monoxide ($CO$).
• Titanium Dioxide ($TiO_2$) Nanoparticles: Used in photocatalytic water purification to degrade organic pollutants under UV/solar light.

1. Targeted Drug Delivery:

• Nanocarriers (liposomes, polymeric nanoparticles, dendrimers) functionalized with target ligands selectively deliver toxic chemotherapy drugs directly to tumor cells (EPR effect), minimizing side effects on healthy tissues.

2. Bio-Imaging & Diagnostics:

• Quantum Dots (CdSe/ZnS): Semiconductor nanoparticles with size-tunable fluorescence used for cellular tracking and cancer imaging.
• Superparamagnetic Iron Oxide Nanoparticles (SPIONs): MRI contrast enhancement agents.

3. Antimicrobial Agents:

• Silver Nanoparticles ($AgNPs$): Incorporated into wound dressings, surgical implants, and catheters to eradicate antibiotic-resistant bacterial biofilms.

Conductometric titration determines the equivalence point by measuring changes in electrical conductivity of the solution as a titrant is added. Conductivity ($\kappa$) depends on the number and ionic mobility of free ions:

• Ionic mobility order: $H^+ (350) > OH^- (198) \gg Na^+ (50) > Cl^- (76)$ (in $\Omega^{-1} \text{cm}^2 \text{mol}^{-1}$).

• Chemical Reaction:

1. Before Equivalence Point:

• As $NaOH$ is added to $HCl$, highly mobile $H^+$ ions (mobility 350) are neutralized to form unionized $H_2O$ and replaced by much slower $Na^+$ ions (mobility 50).
• Consequently, solution conductivity steeply decreases along a linear line until the acid is fully neutralized.

2. At Equivalence Point ($V$):

• Conductivity reaches a sharp minimum, containing only $Na^+$ and $Cl^-$ ions.

3. After Equivalence Point:

• Adding excess $NaOH$ introduces highly mobile free $OH^-$ ions (mobility 198) along with $Na^+$ ions.
• Conductivity steeply increases along a linear line.

4. Locating the Equivalence Point:

• The intersection of the two extrapolated straight regression lines gives the exact equivalence volume of $NaOH$ without relying on color indicators.