Chemistry 1st Ch 02 Qualitative Chemistry

Chemistry - First Paper Chapter 2: Qualitative Chemistry Selected Questions and Answers (HSC English Version) 0.1 Chapter 2: Qualitative Chemistry Group A: Knowledge Based Questions [At a Glance] (1) Rutherford’s Atom Model Based: 1. What is alpha-particle? [Syl. B. 2016, 2017; R. B. 2016, 2019; Brd. Q. 2018] Answer: An alpha-particle (α) is a helium nucleus (He2+), consisting of two protons and two neutrons, with a +2 charge and a mass of 4 amu. 2. Which metal-plate was used in α-particle scattering expt.? Answer: A very thin gold foil (about 0.0004 cm thick) was used. 3. What is atomic nucleus? Answer: The atomic nucleus is the small, dense, positively charged central core of an atom containing all of its protons and neutrons. 4. What is the basis of Rutherford’s atom model? Answer: The basis of Rutherford’s atom model is his α-particle scattering experiment. 5. What is Maxwell’s electromagnetic theory? Answer: Maxwell’s theory states that any charged particle moving continuously in a circular path emits electromagnetic radiation continuously and loses energy. (2) Bohr’s Atom Model Based: 1. What is the basis of Bohr’s atom model? Answer: The basis of Bohr’s atom model is Max Pla

(3) Quantum Mechanical Atom Model Based: 1. What are quantum numbers? [B. B. 2016; J. B. 2016] Answer: Quantum numbers are a set of four numbers used to completely describe the size, shape, spatial orientation of an orbital, and the spin of an electron. 2. Write the equation for radius of nth orbit of electron. Answer: The radius is given by rn = n2h2 4π2mZe2 . 3. Write the equation for electron-energy in nth orbit. Answer: The energy is given by En = −2π2mZ2e4 n2h2 . 4. What is orbital? [J. B. 2015; Ctg. B. 2017] Answer: An orbital is a 3D region in space around the nucleus where the probability of finding an electron is maximum (usually > 90%). 5. What is sub-shell of electron? [Syl. B. 2016; D. B. 2017] Answer: A sub-shell is a subdivision of a principal energy level, designated by the azimuthal quantum number l (e.g., s, p, d, f). 6. What is node? Answer: A node is a region around the nucleus where the probability of finding an electron is zero. 7. How many d-orbitals are possible? Answer: There are 5 possible d-orbitals (m = −2, −1, 0, +1, +2). 8. What is isotope? [B. B. 2015; R. B. 2019] Answer: Isotopes are atoms of the same element having the same atomic number but differen

Answer: The wavelength range of visible light is from 380 nm to 780 nm. 5. What is the range of IR-rays? Answer: The IR region lies just beyond the red end of the visible spectrum, ranging from 780 nm to 1 mm. 6. What is the range of UV-range? Answer: The ultraviolet (UV) range spans from 10 nm to 380 nm. 7. Write Rydberg equation. Answer: The Rydberg equation is 1 λ = ¯ν = RH × Z2  1 n2 1 −1 n2 2  . 8. What is Lymen series? Answer: The Lyman series forms when an electron drops to the first energy level (n1 = 1). It falls in the UV region. 9. What is Balmer series? Answer: The Balmer series forms when an electron drops to the second energy level (n1 = 2). It falls in the visible region. 10. How is fake currency-note detected? Answer: Fake currency notes are detected using UV rays, which cause the fluorescent phosphors embedded in real notes to glow brightly. 11. What is fluorescence? Answer: Fluorescence is the emission of light by a substance almost instantaneously after absorbing light or other electromagnetic radiation. 12. What is the use of IR-theremograph of human body? Answer: An IR-thermograph maps the heat emitted by the skin to detect abnormalities in blood circulation,