Science Majorship: Chemistry Session 1 Diagnostics

The session begins with fundamental chemistry questions. Question 1 classifies a dilute aqueous potassium nitrate solution as a homogeneous mixture. Question 2 distinguishes between elements and compounds by asking which can be chemically decomposed, identifying ammonia (a compound) as decomposable, unlike elements such as oxygen or silicon. Question 3 introduces the simplest alkene, ethene, highlighting its double bond, sp2 hybridization, and trigonal planar molecular geometry.

Question 4 establishes that a neutral atom must contain an equal number of protons and electrons, clarifying the relationship between electrical charge and particle counts in atoms and ions. Question 5 defines 'formula mass' as the sum of atomic masses in a molecule, distinguishing it from atomic weight and isotopic mass. Question 11 explains molecular and empirical formulas, illustrating how the empirical formula is the simplest whole-number ratio of atoms in a compound.

Question 12 focuses on the Pauli Exclusion Principle, stating that no two electrons in an atom can have the same four quantum numbers. This is further explained with analogies for the Aufbau Principle and Hund's Rule. Question 13 discusses electron energy levels, noting that electrons in higher energy levels (e.g., the third energy level) possess more energy and are less stable compared to those in lower energy levels.

Question 14 describes the properties of a semi-metal (metalloid) – shiny, brittle, poor electrical conductivity, and high melting point, distinguishing it from metals and non-metals. Question 15 confirms that elements in the Periodic Table are arranged by increasing atomic number, not atomic mass. Questions 16 and 17 differentiate between 'gas' (naturally gaseous at room temperature) and 'vapor' (a gas formed from a substance that is liquid or solid at room temperature), and outline the physical properties of solids, liquids, and gases, emphasizing the slow diffusion rate in solids.

Questions 18 and 19 define physical and chemical properties, as well as intensive and extensive properties. A physical property is observable without changing identity, while a chemical property involves a composition change. Intensive properties (like density) are independent of amount, unlike extensive properties (like mass). Questions 20, 28, 29, and 30 cover chemical reactions, defining reactants, products, and the law of conservation of mass, which states that the total mass of reactants equals the total mass of products in a closed system. Question 27 identifies baking soda reacting with vinegar as a chemical change due to the formation of a new substance.

Questions 8, 23, 26, 32, and 33 delve into various separation techniques. Chromatography separates mixtures based on solubility and molecular polarity (e.g., ink dyes). Filtration is used for insoluble solids from liquids (e.g., sand from water). Evaporation recovers dissolved solids. Magnets separate magnetic materials (e.g., iron filings from sand). The 'DFE' sequence (Dissolve, Filter, Evaporate) is explained for separating salt from sand.

Question 34 clarifies that isotopes of an element have the same number of protons but different numbers of neutrons. Question 35 identifies 'Proterium' as a non-existent isotope of Hydrogen, while Protium, Deuterium, and Tritium are actual isotopes. Question 36 describes ionic compounds as being formed between a metal and a non-metal via electron transfer. Question 37 asks for the common name of hydrochloric acid ('muriatic acid'). Question 40 demonstrates classical naming for ionic compounds with transition metals, identifying Fe₂(SO₄)₃ as Ferric sulfate.

Question 38 explains that a neutral atom becomes a cation by losing electrons. Question 39 defines an ion as an atom or group of atoms with a net positive or negative charge. Question 41 connects balanced chemical equations to the law of conservation of mass. Question 42 specifies '(aq)' as the symbol for a substance in an aqueous solution. Question 49 highlights Sodium-24 as an isotope used in medicine to detect blood clots. Finally, Question 50 refers to the Law of Conservation of Mass as the 'law of indestructibility of matter'.