Chemistry 2nd Ch 01 Environmental Chemistry

Chemistry - Second Paper Chapter 1 : Environmental Chemistry HSC 2028 (English Version) - Question Bank Creative Questions Units of R 1. C.G.S. unit: R = 8.316 × 107 erg K−1 mol−1 Answer: Derived from P = 76 cm Hg = 76 × 13.6 × 981 dyne cm−2, V = 22400 cm3. Then R = PV nT = (76×13.6×981)×22400 1×273.15 ≈8.314 × 107 erg K−1 mol−1. 2. S.I. unit: R = 8.316 Joule K−1 mol−1 Answer: Derived from P = 101325 Pa, V = 22.414×10−3 m3. Then R = PV nT = 101325×22.414×10−3 1×273.15 ≈ 8.314 J K−1 mol−1. 3. Litreatm unit: R = 0.082 Litre-atm K−1 mol−1 Answer: Derived from P = 1 atm, V = 22.414 L. Then R = PV nT = 1×22.414 1×273.15 ≈0.0821 L atm K−1 mol−1. A. Knowledge Based Questions 1. What is TDS? [Dh.B.16] Answer: TDS (Total Dissolved Solids) is a measure of the dissolved combined content of all inor- ganic and organic substances present in a liquid in molecular, ionized, or micro-granular suspended form. 2. What is mole fraction? [R.B.16] Answer: Mole fraction is the ratio of the number of moles of a speci c component to the total number of moles of all components present in a mixture. 3. What is Charles's law? [R.B.16] Answer: Charles's law states that at constant pressure, the volume of

Answer: Acid rain is rainfall made su ciently acidic by atmospheric pollution (usually containing dissolved sulfur dioxide and nitrogen oxides) that it causes environmental harm, typically with a pH below 5.6. 8. What is BOD? Answer: BOD (Biochemical Oxygen Demand) is the amount of dissolved oxygen required by aerobic biological organisms to break down organic material present in a given water sample at certain temperature over a speci c time period. 9. What is COD? [J.B., Ch.B.16] Answer: COD (Chemical Oxygen Demand) is an indicative measure of the amount of oxygen that can be consumed by reactions in a measured solution, used to quantify the amount of oxidizable pollutants found in surface water or wastewater. 10. What is real gas? [Co.B.16, D.B19, B.B19, Dn.B19] Answer: A real gas is a non-hypothetical gas whose molecules occupy space and have intermolecu- lar interactions, therefore deviating from the ideal gas law at high pressures and low temperatures. 11. What is STP? [Dn.B.16, R.B19] Answer: STP (Standard Temperature and Pressure) is de ned as a temperature of 273.15 K (0◦C) and an absolute pressure of exactly 1 atm (101.325 kPa). 12. What is absolute zero temperatur

B. Understanding Based Questions 1. Why is the pressure of real gas lower than the pressure of ideal gas? [Dh.B.16] Answer: In a real gas, there are attractive intermolecular forces between molecules. As a molecule approaches the container wall to exert pressure, it is pulled back by adjacent molecules, decreasing the force of impact. An ideal gas has no such attractive forces, leading to a higher pressure. 2. AlCl3 is an acidic substance - explain. [R.B.16] Answer: According to the Lewis acid-base theory, an acid is an electron-pair acceptor. In AlCl3, the aluminum atom has an incomplete octet (6 valence electrons). It can accept a lone pair of electrons from a base (such as water or ammonia) to complete its octet, thus acting as a Lewis acid. 3. HCO3  is an amphoteric substance - explain. [S.B.16] Answer: According to the Brønsted-Lowry theory, an amphoteric substance can act as both a proton donor and a proton acceptor. HCO3  can donate a proton to become CO32 (acting as an acid) or accept a proton to become H2CO3 (acting as a base). 4. Why is ammonia called a Lewis base? Explain. [Co.B.16] Answer: A Lewis base is a substance that can donate a lone pair of electrons. In a