PCC/PCD 101 Pharm. Analytical Chemistry I Lecture Notes PDF

PCC /PCD 101 Pharm. Analytical Chemistry I Fall 2024/2024 – Lecture week 4  Analytical Chemistry Quantitative Analysis Qualitative Analysis → determination of the identity (type) of...

PCC /PCD 101 Pharm. Analytical Chemistry I Fall 2024/2024 – Lecture week 4  Analytical Chemistry Quantitative Analysis Qualitative Analysis → determination of the identity (type) of a → determination of the concentration (amount) substance in a sample. of a substance in a sample. eg: Cations and Anions eg: Volumetric Analysis [Titrimetry]  Volumetric Analysis → Type of Quantitative Analysis based on measuring the amount (volume) of titrant (Standard solution) (known concentration) that reacts with the analyte (sample) (unknown concentration) to reach equivalence point in a process called titration. Burette Titration → Process of slow addition of titrant from the burette to the sample solution in the conical flask till complete reaction occurs between them. Equivalence point → A point in the titration at which the amount of added titrant is chemically equivalent to the amount of the sample. Conical Flask → It is a theoretical point [can be calculated]  Volumetric Analysis End point → A point in titration at which a physical change is observed [USING INDICATOR] associated with the condition of equivalence. It is a practical point which can't be calculated, but it is found after the titration process. Titration = End point - Equivalence point Error Indicator → Substance added to the analyte solution in the conical flask during the titration to make an observable physical change (end point) at or near the equivalence point  Volumetric Analysis Typical indicator changes: 1. Appearance or disappearance of color..... 2. Color change. 3. Appearance or disappearance of turbidity. eg: Phenol Phthalein (ph. ph.): Pink (Basic medium) Colorless (Acidic or neutral) Methyl orange (m.o.): Red (Acidic) Orange (Neutral) Yellow (Basic)  Volumetric Analysis Titrant→ a standard solution added from the burette into the titration vessel containing the analyte being titrated. Standard Solution → it is a solution of known concentration used to carry out volumetric analysis. Characteristics of ideal standard solution for titration: 1. Concentration must be stable over long time intervals. 2. Reaction with analyte must be rapid to give good end points. (reliable) 3. Undergo selective simple reaction with the analyte and can be demonstrated with a simple balanced chemical equation. Standard Solutions are classified as primary and secondary  1. Primary standard solution 1. Prepared by dissolving directly a known amount of primary standard substance in Examples of 1o Std: a measured volume of water. {Acids} : Benzoic acid, oxalic acid, potassium acid phthalate (KHC804H4), sulfamic acid (HS03NH2) 2. Its concentration can be calculated from the weight of the solute and the volume {Bases} Na2CO3, Borax (Na₂B4O7.10H20) of the solution. {Salts} KCI, NaCl M = wt x 1 Mwt V {Oxidizing agents} K2Cr2O7, Cerric ammonium nitrate, Arsenic oxide, potassium iodate (KIO4) 3. Its concentration does not change by time {Reducing agents} Sodium oxalate, Arsenious oxide. (years). 1. Primary standard solution Characteristics of primary standard substance: 1) Must be very pure [Reference material] 2) Stable and not affected by air (O2, CO2) 3) High Molecular (formula) weight, to minimize the weighing error (negligible) 4) Ease availability at modest cost. 5) Soluble in titration medium. {N.B} NaOH is not primary standard because it is hygroscopic. HCl is also not 1° std because it is volatile  2. Secondary standard solution eg: HCI, NaOH Its concentration can't be calculated from the weight of the solute and the volume of the solution because both may change by time. :. The concentration of 20 std changes by time ( not reliable) and needs regular standardization to know its concentration. Standardization is done by 2 methods: 1. Titration against primary standard solution. 2. Titration against a previously standardized secondary standard solution.  Requirements of reactions used for volumetric analysis 1] Simple single reaction and described by a balanced chemical equation. 2] Must be complete [Reaction must be quantitative, where equivalent amount of analyte and titrant reacts together]. 3] Must be rapid to give sharp end points. 4] A suitable method for end point detection should be available. (N.B) At equivalence point: Amount of analyte = Amount of titrant  Methods of Expressing Concentrations 1] Molar Concentration (Molarity) [M] Number of moles of chemical species in one liter of the solution. M = moles / VL Molarity = no. of moles of solute = no. of millimoles of solute VL of solution VmL of solution Unit of Molarity is M (mole/L) no. of moles of solute = M x VL = Wt (g) / Mwt no. of millimoles of solute = M x VmL = Wt (mg) / Mwt Preparation of By dissolving 1 mole (Mwt) of 1 Molar (1 M) a substance in 1 L of H2O. solution 1 M NaOH → 40g in 1 L H₂O 1 M HCI → 36.5g in 1 L H₂O 1 M H2SO4 → 96 g in 1 L H₂O  Methods of Expressing Concentrations 2] Normal Concentration (Normality) [N] Number of equivalents of chemical species in one liter of the solution. N = Equivalents/ VL Molarity = no. of equivalents of solute = no. of milliequivalents of solute VL of solution VmL of solution Unit of Normality is N (Equivalent/L) no. of Equivalents of solute = N x VL = Wt (g) / Eq.wt no. of milliequivalents of solute = N x VmL = Wt (mg) / Eq.Wt  Methods of Expressing Concentrations Calculation of equivalent weight (Eq.wt) Eq. wt = M. wt / n n: number of H+ released or consumed in neutralization reaction. n depends on the type of reaction (Neutralization, precipitation, complexation, Redox) * HCI, HBr, HI, CH3COOH (monoprotic acids) ↓ n=1 Eq.wt = Mwt/1  Methods of Expressing Concentrations * H2SO4 (strong diprotic acid) REMEMBER: ↓ n=2 N= n M Eq.wt = Mwt/2 N: normaility M : Molarity * NaOH, KOH (monobasic base) n=1 n : number of H+ released or consumed in neutralization reaction. ↓ n=1 No. of equivalents = n x no. of moles Eq.wt = Mwt/1 Ca(OH)2, Ba(OH)2 (dibasic base) ↓ n=2 Eq.wt = Mwt/2 Preparation of By dissolving 1 equivalent 1 Normal (1 N) (Eq.wt) of a substance in 1 L solution of H2O. 1 N NaOH → 40/1 g in 1 L H₂O 1 N H2SO4 → 96/2 g in 1 L H₂O  Methods of Expressing Concentrations 3] Percent Concentration: ( expressed in terms of %) a) Weight % w/w = wt of solute / wt of solution x 100 % 37 % W/W HCl → 37 g HCl in 100 g solution b) Volume % v/v = Volume of solute / volume of solution x 100 % 5 % Methanol→ 5 mL methanol in 95 mL H2O c) Weight/Volume % w/v = wt of solute(g)/volume of solution(mL) x100% 10 % AgNO3 → 10 g AgNO3 in 100 mL solution. N.B. % w/v → unit: g % , g / 100 mL , %  Methods of Expressing Concentrations 4] Parts per Million: ( used to express very low concentrations) 1 ppm = 1 mg/L = 1 µg/mL = 1 ng / µL  Treatment of Titration Data At Equivalence point: No. of milliequivalents sample = No. of milliequivalents titrant N. VmL sample = N. VmLtitrant Wt (mg) /EqWt Sample = N. VmLtitrant VmL Titrant = E.P. No. of millimoles sample = No. of millimoles titrant x R M. VmL sample = M. VmLtitrant Wt (mg) /M.Wt Sample = M. VmLtitrant R (Molar Ratio) = mmoles Sample / mmoles Titrant Examples: Sample: HCl and Titrant : NaOH Sample: H2SO4 and Titrant : NaOH HCl + NaOH → NaCl + H2O H2SO4 + 2 NaOH → Na2SO4 + H2O N. VmL HCl = N. VmL NaOH N. VmL H2SO4 = N. VmL NaOH M. VmL HCl = M. VmL NaOH x R (1/1) M. VmL H2SO4 = M. VmL NaOH x R (1/2) Sample: HCl and Titrant : Ba(OH)2 Sample: NaOH and Titrant : H2SO4 2HCl + Ba(OH)2 → BaCl2 +2H2O H2SO4 + 2 NaOH → Na2SO4 + H2O N. VmL HCl = N. VmL Ba(OH)2 N. VmL NaOH = N. VmL H2SO4 M. VmL HCl = M. VmL Ba(OH)2 x R (2/1) M. VmL NaOH= M. VmL H2SO4 x R (2/1)  DILUTION PROCESS C.V before dilution = C.V After Dilution (C : Concentration, M, N, g%, g/mL, ppm, …..) Important Conversions