Analytical Chemistry Basics - Lecture Notes PDF

Basics of Analytical Chemistry (chm201, chm219B) Dr Ibrahem M A Hasan  Assessment Type of Assessment Marks Theoretical 40 Practical 20 Oral 10 Midterm 10 Cont. Assess. 20 Total...

Basics of Analytical Chemistry (chm201, chm219B) Dr Ibrahem M A Hasan  Assessment Type of Assessment Marks Theoretical 40 Practical 20 Oral 10 Midterm 10 Cont. Assess. 20 Total 100 2  Weekly Hours Theoretical Practical Total Credit 1 3 4 2 Textbooks 1. Douglas A. Skoog, Donald M. West, F. James Holler, Stanley R. Crouch, Fundamentals of Analytical Chemistry, 10th edition, 2022, Cengage Inc., MA, USA. 2. Daniel C. Harris, Charles A. Lucy, Quantitative Chemical Analysis, 9th edition, 2016, W. H. Freeman and Company, NY, USA.  Syllabus Volumetric analysis Acid-base titrations – Strong acid (SA) with strong base (SB) – Weak base (WB) with SA – Weak acid (WA) with SB – WA with WB – Ploybasic acids with SB – Anions of WA with SA 4  Syllabus Precipitation titrations – Introduction – Fagan method (use of adsorption indicators) – Liebig's method (turbidity method) Oxidation-Reduction titrations – Introduction – End point detection Complex formation titrations 5 Volumetric Analysis 6 ITEMS Definition of some terms Classification of reactions in volumetric analysis Concentration of solution General method of computing results Preparation of standard solutions Theory of acid-base titration 7  Definition of some terms Volumetric analysis: any method of quantitative chemical analysis in which the amount of the substance is determined by measuring the volume (titrimetric analysis). Titration: process of adding the standard solution to the unknown until the reaction is just complete. Titrant: reagent of known concentration. Titrand: substance being titrated. Standard solution: solution of accurately known concentration. Standardization: a process to determine the exact concentration of a solution of unknown concentration by titrating with a primary standard. Direct titration: titrant is added to the analyte until the reaction is complete.  Definition of some terms End point: – The point at which the reaction is observed to be complete. – The end point in volumetric analysis is the signal that tells the analyst to stop adding reagent and make the final reading on the burette. – End point is observed with the help of an indicator. Equivalence point: – The point at which an equivalent or stoichiometric amount of titrant is added to the analyte based on the stoichiometric equation.  Reaction requirements For a reaction to be used in volumetric analysis, it must fulfill the following conditions: 1) The substance to be determined should react completely with the reagent in stoichiometric or equivalent proportions. 2) The reaction should be practically immediate or proceed with very high speed. 3) There must be a marked change in some physical or chemical property of the solution at the equivalence point. 4) An indicator should be available. 10 Classification of reactions in volumetric analysis Acid-base (Neutralization) Precipitation Complexometric Reduction- oxidation Classification of reactions in volumetric analysis 1) Neutralization reactions: Acidimetry: the titration of free bases or those formed by hydrolysis of salts of weak acids, with a standard acid. Alkalimetry: the titration of free acids or those formed by hydrolysis of salts of weak bases, with a standard base. These reactions involve the combination of hydrogen and hydroxyl ions to form water. HCl + NaOH NaCl + H2O H+ + OH- HOH 12 Classification of reactions in volumetric analysis 2) Complex formation reactions: depend upon the combination of ions, other than hydrogen or hydroxide ions, to form a soluble slightly dissociated ion or compound. Examples: – 2CN- + Ag+ [Ag(CN)2]- – 2Cl- + Hg 2+ [HgCl2] – Cu(H2O)42+ + 2EDTA → [Cu(EDTA)2]2- + 4H2O EDTA: Ethylenediamine tetraacetic acid 13 Classification of reactions in volumetric analysis 3) Precipitation reactions: depend upon the combination of ions, other than hydrogen or hydroxide ions, to form a simple precipitate. Example: Ag+ + NO3- + Na+ + Cl- → AgCl + Na+ + NO3- 4) Reduction oxidation (Redox) reactions: involve a change in valences or transfer of electrons. Example: MnO4- + 5Fe2+ + 8H+ → Mn2+ + 5Fe3+ + 4H2O 14  Concentration of solution Concentration: is the amount of solute in a given amount of solution (rarely “in amount of solvent”). UNITS: 1. Percent composition: a. % mass (% m/m) = (mass of solute/mass of soln) x 100 b. % volume (% v/v) = (volume of solute/volume of soln) x 100 c. % mass/volume (% m/v) = (mass of solute/volume of soln) x 100 2. Molarity (M) = moles of solute/liter of soln (v) 15  Concentration of solution UNITS: 3. Molality (m) = moles of solute/kg of SOLVENT 4. Parts per million (ppm) = (mass of solute/mass of soln) x 106 5. mole fraction (x) = moles of solute/total moles of soln 6. Mass per volume (g/L) = mass of solute/volume of soln 7. Normality (N) = gram equivalents of solute/liter of soln 16  Computing results At the end point: Normality = gram equivalents/liters Normality = milligram equivalents/milliliters (ml) Number of mg equivalents = Number of ml x Normality When a standard solution (A) reacts with unknown solution (B): VA x NA = VB x NB VA x MA = VB x MB Where VA and VB are the reacted volumes of solutions A and B, respectively and NA and NB are the normalities of solutions A and B, respectively Generally, VA x CA = VB x CB Where CA and CB are concentrations of solutions A and B in same units 17  Dilution Dilution: is adding extra solvent to decrease the concentration of a soln. The amount of solute remains constant before and after dilution, but the concentration decreases. Before dilution After dilution Conc1 x Vol1 = Conc2 x Vol2 M1 x V1 = M2 x V2 % 1 x V1 = % 2 x V2 Concentrations and volumes can be most units as long as they are consistent. 18 19