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TITRATIONS IN NON-AQUEOUS SOLVENTS

TITRATIONS IN NON-AQUEOUS SOLVENTS. WATER, as SOLVENT. ☻ cheap, clean (can easily be purified) ☻ high relative permittivity ( ε ): good solvent. ADVANTAGES:.  0 - 100 ° C temperature range  apolar substances can not be disolved

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TITRATIONS IN NON-AQUEOUS SOLVENTS

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  1. TITRATIONS IN NON-AQUEOUS SOLVENTS

  2. WATER, as SOLVENT ☻cheap, clean (can easily be purified) ☻high relative permittivity (ε): good solvent ADVANTAGES: 0 - 100 °C temperature range apolar substances can not be disolved Kw = 10−14, therefore Kd ≤ 10−7 unmeasurable DISADVANTAGES: WATER actively participates in all type of reactions: - acid and base: acid-base reactions take place through connection to water first (amphoteric) - complex formation: cations: aqua complex anions : H-bond - precipitation: dissolves precipitate of ionic lattice (high hydration energy) - oxidant and reductant; range of redox potential: 0 −1,23 V theoretical -0.8 − 2,1 V practical

  3. CLASSIFICATION of SOLVENTS ACIDIC (protogene): H2SO4, CH3COOH, HCOOH, acetone proton donor BASIC (protophyl): pyridine, liq. NH3, amins, dioxane proton acceptor AMPHOTERIC (amphiprotic): H2O, alcohols, acetonitrile APROTIC: liquid SO2 INERT: CCl4, CHCl3, benzene, carbohydrates

  4. REACTIONS in NON-AQUEOUS SOLUTIONS ☻neutralization (protolytic solvents) ≈ 90 % ☻ complex formation, precipitation, redox≈ 10 % NEUTRALIZATION ANALYSIS in NON-AQUEOUS SOLVENTS − pH scale depends on the value of KHL = [H2L+][L−] AUTOPROTOLYSIS EQUILIBRIA determines the ionic product : solvent K pH scale neutr. point 2 H2O H3O+ + OH−10−140 - 147 2 CH3COOH CH3COH2+ + CH3COO− 10−13 0 - 13 6,5 2 NH3  NH4+ + NH2− 10−32 0 - 32 16 2 C2H5OH C2H5OH2+ + C2H5O− 10−19 0 - 19 9,5

  5. REACTIONS in NON-AQUEOUS MEDIUM − Brönsted equation can be used − reactions take place through reaction of acids or bases with the solvents E.g. HClO4 + pyridine (Py) in glacial acetic acid K =[CH3COOH2+][CH3COO−] = 10−13 acid: HClO4+CH3COOH ClO4− +CH3COOH2+ base:Py+CH3COOHPyH++CH3COO− ClO4−+ CH3COOH2+ PyH++CH3COO− PyH+ClO4−+2 CH3COOH 2 CH3COOH

  6. ADVANTAGES of USING NON-AQUEOUS SOLVENTS ☻1.More than 3 acids/bases can be measured in mixture due to the wider pH range compared to water E.g.methyl-ethyl-ketone water 0 - 25.7 pH range 0 - 14 pH range 5 comp. measurable max. 3 acids (3 x ΔpH(4) = 12) HClO4 - HCl - Salicylic acid - Acetic acid - Phenol (can titrated with TBAH (C4H9)4N+OH−)

  7. ADVANTAGES of USING NON-AQUEOUS SOLVENTS ☻2.Differentiation- levellingeffect(Kd~ 10−12 can be measured) a) Differentiation effect: in water:HClO4 ≈ HCl ≈ HNO3 in CH3COOH:HClO4> HCl > HNO3 in HF:medium > weak > base acid Conclusions: Strong acids (in water) can separetely be measured in acidic solvents Strong bases - ″- in basicsolvents b) Levelling effect: in water:HCl > CH3COOH > benzoic acid inpyridine:HCl ≈ CH3COOH ≈ benzoic acid Conclusions: Weak acids (in water) can be measured in basic solvents Weak bases - ″ -in acidic solvents EXPLANATION by the protonaffinity

  8. ADVANTAGES of USING NON-AQUEOUS SOLVENTS ☻3.Determination of organic acids and bases which have a limited solubility in water. ☻4.Application of new reagents and indicators is possible due to DISADVANTAGES of USING NON-AQUEOUS SOLVENTS expensive volatile toxic  removal of water is necessary, can take water (humidity) from the air

  9. STANDARD SOLUTIONS −HClO4 in glacial acetic acid − HCl in propylene-glycol /chloroform mixture ACIDIC : application: - weak bases: Kb : 10−7 − 10−12 e.g. aromatic amines, amides, alcaloides, etc. - high-molecular-weight organic bases, that have limited solubility in water E.g. Determination of „Lidocain” (Lidocainum Ph.Hg. VII.) −TBAH (C4H9)4N+OH−)in pyridine − KOH in ethanol BASIC : application: - weak acids: Ka : 10−7 − 10−12 e.g. carboxylic acids, phenols, enols etc. - high-molecular-weight organic acids, that have limited solubility in water

  10. END POINT DETECTION −phtaleins (phenolphtalein) (e.g. in pyridine) CHEMICAL: (INDICATORS) −azo compounds (methyl red) (e.g. in alcohol) −crystal violet (in glacial acetic acid) R +  C-R  R ibolya R +R-H 2+   C-R + H+C - R  R R ibolya zöldeskék R +R-H 2+ R-H 3+    C-R + H+C - R + H+ C-R   R R R-H violet green yellow −potentiomety : glass electrode in glacial acetic acid − conductometry INSTRUMENTAL:

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