http:\\asadipour.kmu.ac.ir 24 slides Typical Applications of Neutralization Titrations Elemental Analysis 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Keldahl Nitrogen Analysis 1)With HCl 2)With H3BO3 13920208 http:\\asadipour.kmu.ac.ir 24 slides

Apparatus used in Kjeldahl II. Distillation & absorption apparatus I. Digestion apparatus 13920208 (I) http:\\asadipour.kmu.ac.ir 24 slides (II)

http:\\asadipour.kmu.ac.ir 24 slides Keldahl Nitrogen Analysis (1) Step 1: Kjeldahl digestion (decomposing and dissolving) Step 2: Neutralization by adding base Step 3: Distillation NH3 into excess HCl standard Step 4: Titrating unreacted HCl with NaOH standard 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Example: A typical meat protein contains 16.2% (w/w) nitrogen. A 0.500 mL aliquot of protein solution was digested, and the liberated NH3 was distilled into 10.00 mL of 0.02140 M HCl. The unreacted HCl required 3.26 mL of 0.0198 M NaOH for complete titration. Find the concentration of protein (mg protein/ml) in the original sample. Solution: 13920208 http:\\asadipour.kmu.ac.ir 24 slides

Keldahl Nitrogen Analysis (2) 1. Digestion NCOC + H2SO4 （NH4）2SO4 + CO2 + SO2 + H2O 2. Neutralization &distillation 2NaOH +（NH4）2SO4 2NH3↑+Na2SO4 + 2H2O 3. Absorption by boric acid :      2NH3 + 4H3BO3 （NH4）2B4O7 + 5H2O 4. Titration by strong acid （NH4）2B4O7 + 5H2O + 2HCl 2NH4Cl + 4H3BO3 (* NCOC, N containing organic compounds, N:HCl = 1:1) 催化剂 煮沸 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Example: A typical meat protein contains 16.2% (w/w) nitrogen. A 0.500 mL aliquot of protein solution was digested, and the liberated NH3 was distilled into 100.00 mL of 0.0200 M H3BO3. The mixture required 3.26 mL of 0.0198 M HCl for complete titration. Find the concentration of protein (mg protein/ml) in the original sample. Solution: 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides The Determination of Inorganic Substances Ammonium Salts are conveniently determined by conversion to ammonia with strong base followed by distillation. Ammonia is collected and titrated as in the Kjedahl method. Nitrates and Nitrites ions are first reduced to ammonium ion by Devarda’s alloy (50% Cu, 45% Al, 5% Zn) or Arnd’s alloy (60% Cu, 40% Mg). Granules of the alloy are introduced into strongly alkaline solution of the sample in Kjedahl flask. The ammonia is distilled after reaction is complete. 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides CO2 & CO32- chemistry pKa1=6.38 pKa2=10.33 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides CO2 & CO32- chemistry Na2CO3 →2Na+ + CO32- CO32- HCO3-  H2CO3 pKb1=3.64 pKb2=7.62 13920208 http:\\asadipour.kmu.ac.ir 24 slides

Titration of Na2CO3 with HCl Step 1: Na2CO3 + HCl  NaHCO3 + NaCl Step 2: NaHCO3 + HCl  H2CO3 + NaCl Overall: Na2CO3 + 2HCl  H2CO3 + 2NaCl Phenolphthalein pH BCG n=1 Ve1 n=2 Ve2 Equivalents of HCl added 13920208 http:\\asadipour.kmu.ac.ir 24 slides

Determination of Carbonate in a Sample A 1.2040-g sample containing sodium carbonate and inert material was dissolved in water and titrated to the bromcresol green end point, requiring 32.50 mL of 0.1020 M HCl. Calculate the % Na2CO3 in the sample. BCG For the BCG endpoint, the reaction is Na2CO3 + 2HCl  H2CO3 + 2NaCl 13920208 http:\\asadipour.kmu.ac.ir 24 slides

Effect of CO2 Absorption on Phenophthalein Endpoint Reaction of CO2 with carbonate solutions CO2(g) + H2O(l) + CO32(aq)  2HCO3(aq) pH of carbonate solutions may be unstable due to exchange of CO2 with atmosphere. This effect may be avoided by excluding air from the titration system. 13920208 http:\\asadipour.kmu.ac.ir 24 slides

Effect of Absorbed CO2 on Titration of Na2CO3 with HCl Ve1 Ve2 Before absorption After absorption Ve1 decreases Ve2 is not affected Use Ve2 for calculations CO2(g) + H2O(l) + CO32(aq) 2HCO3(aq) 13920208 http:\\asadipour.kmu.ac.ir 24 slides

Effect of CO2 Absorption on OH- concentration OH- standard solutions can react with CO2 CO2(g) + 2 OH- → CO32(aq) This effect may be avoided by excluding air from the titration system. In presence of BCG--------no error In presence of Phenol phetalein------- Carbonate Error 13920208 http:\\asadipour.kmu.ac.ir 24 slides

Boiling to Enhance Visual Endpoint in Titration of Na2CO3 with HCl Na2CO3 +HCl  HCO3- NaHCO3 HCO3- +HCl  H2CO3 Boiling removes H2CO3 as gaseous CO2 NaHCO3 + H2CO3 H2CO3(aq)  CO2(g) + H2O 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Titration curves and indicator transition ranges for the analysis of mixtures containing : OH- CO32- Winkler method Mixture of CO32- +OH- 1)Titrate the mixture with H+ In presence of BCG OH-≈ 1H+ --CO32-≈2H+ 2)Excess BaCl2 is added CO32- + Ba2+→BaCO3 --Titrate the mixture with H+ Titrant-≈ OH- 3) Titrant1-titrant2 ≈ CO32- HCO3- OH- CO32- CO32- HCO3- 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Titration curves and indicator transition ranges for the analysis of mixtures containing : OH- CO32- Winkler method Mixture of CO32- + HCO3- 1)Titrate the mixture with H+ In presence of BCG HCO3-≈ 1H+ --CO32-≈2H+ 2)Excess BaCl2 is added CO32- + Ba2+→BaCO3 --Titrate the mixture with H+ Titrant-≈ HCO3- 3) Titrant1-titrant2 ≈ CO32- HCO3- OH- CO32- CO32- HCO3- 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Titration curves and indicator transition ranges for the analysis of mixtures containing : OH- CO32- Mixture of 2 weak acids Mixture of CO32- + HCO3- 1)Titrate the mixture with H+ In presence of BCG (A ml) HCO3-≈ 1H+ -- CO32-≈2H+ 2)Titrate the mixture with H+ In presence of Phenol phetalein (C ml) Titrant≈ CO32- 3) (A-2C)=Bml ≈ HCO3- HCO3- OH- CO32- CO32- HCO3- 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Carbonate and Carbonate Mixtures 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides The Determination of Organic functional Groups Carboxylic acid group Most CA have between 10 –4 > Ka > 10–6. CA are not sufficiently soluble in water for direct titration in this medium. the acid can be dissolved in ethanol and titrated with aqueous base. Alternatively, the acid can be dissolved in an excess of standard base followed by back-titration with standard acid. Sulfonic acid group Sulfonic acids are generally strong acids and readily dissolve in water. Their titration with a base is therefore straightforward. 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Amine group A) titrated in aqueous media. 1) Aliphatic amines generally have Kb on the order of 10–5 and can thus be titrated directly with a solution of a strong acid. 2) Many saturated cyclic amines, such as piperidine, tend to resemble aliphatic amines in their acid-base behavior and thus can be titrated in aqueous media. B) titrated in non-aqueous solvents Many amines that are too weak to be titrated as bases in water are readily titrated in non-aqueous solvents, such as anhydrous acetic acid, which enhance their basicity. 3) aromatic amines such as aniline and its derivatives are usually too weak for titration in aqueous medium (Kb 10–10 ). 4) The same is true for cyclic amines, such as pyridine and its derivatives. 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Ester groups Esters are commonly determined by saponification with a measured quantity of standard base: R1COOR2 + OH–  R1COO – + HOR2 The excess base is then titrated with standard acid. Hydroxyl groups Hydroxyl groups in organic compounds can be determined by esterification with various carboxylic acid anhydrides or chlorides; the two most common reagents are acetic anhydride and phthalic anhydride. (CH3CO)2O + ROH  CH3COOR + CH3COOH The acetylation is ordinarily carried out by mixing the sample with a carefully measured volume of acetic anhydride in pyridine. After heating, water is added to hydrolyze the unreacted anhydride : (CH3CO)2O + H2O  2CH3COOH The acetic acid is then titrated with a standard solution of alcoholic sodium or potassium hydroxide. A blank is carried through the analysis to establish the original amount of anhydride. 13920208 http:\\asadipour.kmu.ac.ir 24 slides

http:\\asadipour.kmu.ac.ir 24 slides Carbonyl groups Many aldehydes and ketones can be determined with a solution of hydroxylamine hydrochloride. The reaction, which produces an oxime, is R1 R1 C=O + NH2OHHCl  C=NOH + HCl + H2O R2 R2 where may be an atom of hydrogen. The liberated HCl is titrated with base. Here, the conditions necessary for quantitative reaction vary. Typically, 30 min suffices for aldhydes. Many ketones require refluxing with the reagents for 1 hr or more. 13920208 http:\\asadipour.kmu.ac.ir 24 slides