Chemistry 2nd Ch 03 Quantitative Chemistry

Chemistry - Second Paper Chapter 3 : Quantitative Chemistry Creative & Short Questions - HSC (English Version) 2 KClO3 −−→2 KCl + 3 O2 2 Pb(NO3)2 −−→2 PbO + 4 NO2 + O2 A. Knowledge Based Questions 1. What is ppm? [R.B.16, J.B.19] Answer: Parts per million (ppm) is a unit of concentration that expresses the mass of solute present in one million (106) parts by mass of the solution. It is commonly used to express trace amounts of contaminants in water or air. For aqueous solutions, 1 ppm is equivalent to 1 milligram of solute per liter of solution (1 mg/L). 2. What is standard solution? [S.B.16] Answer: A standard solution is a solution whose concentration (molarity, normality, etc.) is accurately known. It is prepared by dissolving an exactly weighed amount of a primary standard substance in a speci c volume of solvent, and is used to determine the unknown concentration of other solutions in titration. 3. What is called indicator? [Ch.B.16, S.B.19, R.B.19] Answer: An indicator is a chemical substance, usually a weak organic acid or base, that changes its color over a speci c pH range or in the presence of certain ions. It is used in titrations to indicate the end point (complet

Answer: Iodimetry is a direct volumetric analysis method where a standard solution of iodine (I2) is used as the titrant to directly determine the concentration of reducing agents (such as sodium thiosulfate, arsenite, or sul te) using starch as an indicator. 9. What is called titration? Answer: Titration is a quantitative analytical technique in which a solution of known concen- tration (the titrant) is added gradually from a buret to a known volume of a solution of unknown concentration (the analyte) until the chemical reaction between them is just complete, indicated by an end point. 10. What is neutralization reaction? Answer: A neutralization reaction is a chemical reaction in which an acid and a base react quantitatively with each other to form a salt and water as the only products. In terms of ions, it is the combination of H+ ions from the acid with OH ions from the base to form H2O. 11. What is oxidation number? Answer: The oxidation number (or oxidation state) is a formal integer assigned to an atom in a molecule or ion that represents the number of electrons it has lost, gained, or unequally shared compared to its pure elemental state. It indicates the degree of oxidati

3. BOD of a sample water is 500 ppm. What does it mean? [S.B.16] Answer: BOD (Biochemical Oxygen Demand) is the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample. A BOD of 500 ppm (500 mg/L) means that 500 milligrams of dissolved oxygen are required by bacteria to completely decompose the organic waste present in 1 liter of that water sample. This indicates highly polluted water. 4. Molar solution is a standard solution - explain. [S.B.16] Answer: A standard solution is one whose concentration is accurately known. A molar solution contains exactly 1 mole of solute dissolved in 1 liter of solution (1 M). Since its exact concentration (1 M) is known by de nition and preparation, a molar solution is a standard solution. 5. Why is HNO3 stronger acid than H3PO4? [Ch.B.16] Answer: The acid strength of oxyacids depends on the oxidation number and electronegativity of the central non-metal atom. In HNO3, the oxidation number of N is +5, while in H3PO4, the oxidation number of P is +5. Since both have the same oxidation number, we compare electronegativity. Nitrogen (3.0) is more electronegative and smaller th