FORD FLTM AK 103-02-2001 QUANTITATIVE ANALYSIS OF NITRITE (AS NO2) IN CLEANERS《清洁剂中亚硝酸盐(如二氧化氮)的定量分析》.pdf

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1、 FORD LABORATORY TEST METHOD AK 103-02 Date Action Revisions 2001 01 22 Revised Editorial no technical change A. Cockman 2000 03 22 Revised Editorial no technical change A. Cockman 1990 02 14 Printed copies are uncontrolled Page 1 of 8 Copyright 2001, Ford Global Technologies, Inc. QUANTITATIVE ANAL

2、YSIS OF NITRITE (AS NO2) IN CLEANERS Application This method describes two test procedures for determining the percent nitrite in a cleaner. The procedures are: distillation method by conversion to NH3 (preferred) and the permanganate method. Apparatus Required Analytical Balance - Having a precisio

3、n of +/- 0.1 mg Hot Plate Distillation Apparatus Titration Apparatus Kjeldahl Distillation Flask - 500 mL Erlenmeyer Flask - 500 mL Graduated Cylinder - 100 mL Materials Required Mossy Zinc Reagent grade Ferrous Sulfate Reagent grade Sodium Hydroxide Reagent grade. CAUTION: Corrosive Distilled or De

4、ionized Water 10 ppm max total dissolved solids (ASTM D 1888) FORD LABORATORY TEST METHOD AK 103-02 Page 2 of 8 Copyright 2001, Ford Global Technologies, Inc. Kerosene, Silicone or Strontium Chloride Refer to Note “A“ in the Procedure. CAUTION: Kerosene has a low flash point; strontium chloride is t

5、oxic. Potassium Permanganate Reagent grade. CAUTION: Dangerous fire and explosion hazard. Solutions Required Hydrochloric Acid Solution - 0.5 N Sodium Hydroxide Solution - 30 % cone and 0.5 N Methyl Red Refer to FLTM AZ 102-01 Potassium Permanganate - 0.1 N (KMnO4) Ferrous Sulfate - 0.1 N (FeSO4) Su

6、lfuric Acid - 50 % Conditioning and Test Conditions All test values indicated herein are based on material conditioned in a controlled atmosphere of 23 +/- 2 C and 50 +/- 5 % relative humidity for not less than 24 h prior to testing and tested under the same conditions unless otherwise specified. Pr

7、ocedure for Distillation Method The Distillation Method by Conversion to NH3 is preferred. 1. Place a 0.5 to 1.0 g aliquot of the prepared 1 % solution of cleaner into a 500 mL Kjeldahl distillation flask. 2. A receiving flask containing methyl red indicator and 25 mL of 0.5 N HCl must be in place p

8、rior to starting the distillation. 3. The end of the delivery tube must be immersed in the HCl solution during the distillation. 4. Dilute the sample in the distilling flask to 250 mL with distilled water. 5. Add to this 5.0 g of mossy zinc and 2.0 g of ferrous sulfate. FORD LABORATORY TEST METHOD A

9、K 103-02 Page 3 of 8 Copyright 2001, Ford Global Technologies, Inc. 6. Add 50 mL of a 30 % sodium hydroxide solution being careful not to touch the sides or lip of the flask. 7. Agitate this mixture by swirling. 8. Distillation should then be made for 3/4 to 1 hour until approximately half of the vo

10、lume of liquid in the distilling flask has been recovered in the receiving flask. 9. Wash the condenser and tube with distilled water into the receiving flask. 10. Titrate the excess 0.5 N HCl with 0.5 N NaOH. 11. Calculate the amount of NO2 as follows: % NO2 = A - B x 0.023 x 100 C Where: A = mL of

11、 0.5 N HCl B = mL of 0.5 N NaOH C = Weight of sample, grams Note “A“: On occasion, excessive foaming may take place. Addition of kerosene, silicone or strontium chloride to the distillation flask normally suppresses this foaming tendency. General Notes on the Distillation Method Nitrite, nitrate, am

12、monia and ammonium are quantitatively detected by this method. If two or more of these species are present, the result must be interpreted as total nitrogen. This may be useful information, since the contribution from ammonia, ammonium and nitrite can be determined by alternate methods. Some organic

13、 compounds also partly distill or give off ammonia on distillation with strong alkali. Mono, di-, and tri- ethanolamine, EDTA and other nitrogen-bearing compounds will contribute to the result but not in a quantitative manner. The presence of these nitrogen-bearing compounds is therefore undesirable

14、. For samples containing a low concentration of nitrite, better accuracy can be obtained by analyzing a larger sample. If the observed titration is less than 0.5 mL, the distillation must be repeated with a larger sample. This is necessary to ensure that nitrite is actually present in the sample bei

15、ng analyzed. FORD LABORATORY TEST METHOD AK 103-02 Page 4 of 8 Copyright 2001, Ford Global Technologies, Inc. General Information for the Distillation Method 1. In the basic solution, ferrous sulfate quantitatively reduces nitrite to ammonia in the presence of zinc. The ammonia is distilled into a r

16、eceiving flask containing standard 0.5 N HCl and neutralized. The excess HCl is titrated with standard 0.5 N NaOH. 2. The amount of nitrite in the sample, expressed as % NO2, is calculated as follows: % NO2 = (mL of 0.5 N HCl used to neutralize the NH 3) x 0.023 x 100 weight of sample (grams) 3. The

17、 mathematical factor in the formula is obtained as follows: 0.023 = 0.5 mol HCl x L x mol NH 3 x mol NO 2 x 46.0 g NO 2 L 1000 mL mol HCl mol NH3 mol NO2 4. The method also quantitatively reduces nitrate to ammonia and can be used as an alternative to FLTM AK 113-01. If nitrate is the only nitrogen

18、species present, the amount of nitrate, expressed as % NO3 can be calculated by substituting 0.031 for 0.023 in the formula. Procedure for the Permanganate Method 1. Place a 0.5 to 1.0 g aliquot of the prepared 1 % solution in a 500 mL Erlenmeyer flask. 2. Add distilled water to obtain a total volum

19、e of 200 mL. 3. Add 10 mL of 1:1 sulfuric acid. 4. Add potassium permanganate until a pink color persists. 5. To a fresh sample identical in size to the preliminary sample of material, add this amount of potassium permanganate plus 10 mL excess. 6. Then add 10 mL of 1:1 sulfuric acid. 7. Titrate the

20、 excess of permanganate with ferrous sulfate solution until the pink color is gone. 8. Add a slight excess of ferrous sulfate. 9. Titrate again with permanganate until one drop of permanganate makes a pink color persist. FORD LABORATORY TEST METHOD AK 103-02 Page 5 of 8 Copyright 2001, Ford Global T

21、echnologies, Inc. 10. Record the total volume of permanganate solution used. 11. Record the total volume of ferrous sulfate solution used. 12. Calculate the percent of nitrite as % NaNO2 by the following: % NaNO2 = A - B x 0.003451 x 100 C Where: A = mL of 0.1 N KMnO4 used B = mL of 0.1 N FeSO4 used

22、 C = Weight of sample, grams % NO2 = % NaNO 2 1.5 General Notes for the Permanganate Method Other materials oxidizable by potassium permanganate must be absent. For samples containing a low concentration of nitrite, better accuracy can be obtained by analyzing a larger sample. Glassware may be stain

23、ed by the decomposition of permanganate solutions. Manganese dioxide is readily soluble in HCl. General Information for the Permanganate Method In acid solution, potassium permanganate oxidizes nitrite to nitrate quantitatively. This method can be used to distinguish between nitrite and nitrate sinc

24、e no reaction occurs with the latter. However, if species other than nitrite that are also oxidizable by permanganate are present, they will interfere with the procedure. 1. A preliminary sample is titrated with potassium permanganate in the presence of sulfuric acid until a pink color persists. Rea

25、ction (1) 5 NaNO2 + 2 KMnO4 + 3 H2SO4 5 NaNO3 + K2SO + 2 MnSO4 + 3 H4O2 The products of the reaction are colorless. The pink color will not persist until permanganate is no longer being consumed. FORD LABORATORY TEST METHOD AK 103-02 Page 6 of 8 Copyright 2001, Ford Global Technologies, Inc. 2. To a

26、 fresh sample, identical in size to the preliminary sample, the same amount of potassium permanganate is added plus 10 mL excess. Then sulfuric acid is added. When the acid is added before the permanganate, as in the preliminary titration, there is danger of losing nitrous material by volatilization

27、. 3. The excess permanganate is titrated with ferrous sulfate until the permanganate color is destroyed. Reaction (2) 10 FeSO4 + 2 KMnO4 + 8 H2SO4 5 Fe2(SO4)3 + K2SO4 + 2 MnSO4 + 8 H2O 4. A slight excess of ferrous sulfate is added and the solution is titrated with potassium permanganate until one d

28、rop makes a pink color persist. 5. The amount of nitrite in the sample, expressed as % NaNO2, is calculated as follows: % NaNO2 = A - B x 0.003451 x 100 C Where: A = mL of 0.1 N KMnO4 used B = mL of 0.1 N FeSO4 used C = Weight of sample, grams The volume of 0.1 N KMnO4 used less the volume of 0.1 N

29、FeSO4 used represents the volume of 0.1 N KMnO4 used to oxidize nitrite to nitrate. The mathematical factor in the formula is obtained from the stoichiometry of Reaction (1) and the knowledge that when permanganate is reduced to Mn2+, 5 moles of electrons (equivalents) are consumed per mole of KMnO4

30、. 0.003451 = 0.1 equiv KMNO 4 x L x mol KMnO 4 x 5 mol NaNO 2 L 1000 mL 5 equiv KMnO4 2 mol KMnO4 x 69.00 g NaNO 2 mol NaNO2 Standard Solutions Potassium Permanganate, Standard 0.1 N A. Preparation Weight out 5.0 g of reagent grade potassium permanganate (KMnO4, formula weight = 158.04) and dissolve

31、 it in 1500 mL of distilled water in a 2000 mL beaker. Heat to near boiling for 1 hour, add 5 g of analytical grade filter aid (such as Celite) and cool. Stir well, filter through a fritted glass filter, and transfer to an amber-colored bottle. FORD LABORATORY TEST METHOD AK 103-02 Page 7 of 8 Copyr

32、ight 2001, Ford Global Technologies, Inc. B. General Information When preparing standard solutions of KMnO4, note that the equivalent weight of a substance in an oxidation-reduction reaction is that weight of a substance which produces or consumes one mole of electrons. When permanganate, MnO4- is r

33、educed to Mn2+, 5 moles of electrons are consumed, per mole of KMnO4. Therefore, the equivalent weight of KMnO4 is 20 % of the formula weight. The normality (equivalents/liter) of a KMnO4 solution is therefore 5 times the molar concentration (moles/liter). Aqueous solutions of permanganate are not c

34、ompletely stable because the ion tends to oxidize water. 4 MnO4- + 2 H2O 4 MnO2 + 3 O2 + 4 OH- This decomposition is catalyzed by light, heat, acids, bases, and manganese dioxide. It is therefore important to remove manganese dioxide from a freshly prepared KMnO4 solution by filtration and then to s

35、tore the solution in a dark bottle. Properly prepared permanganate solutions are quite stable. Standardization of 0.1 N Potassium Permanganate A. Procedure Weigh out an accurately known amount (about 0.3 g) of sodium oxalate (Na2C2O4, formula weight = 134.00), dissolve it in 100 mL of distilled wate

36、r in a 300 mL Erlenmeyer flask, add 15 mL of 1:3 sulfuric acid and heat to 80 C. Titrate at a temperature between 70 and 80 C with the potassium permanganate solution, with constant agitation. Add the permanganate slowly and allow the color to fade after each addition until finally a faint pink colo

37、r persists. Calculate the normality of the potassium permanganate solution. B. General Information Potassium permanganate is usually standardized against sodium oxalate. 2 KMnO4 + 5 Na2C2O4 + 8 H2SO4 K2SO4 + 2 MnSO4 + 5 Na2SO4 + 8 H2O + 10 CO2 This reaction proceeds slowly at room temperature. There

38、fore, the sodium oxalate is titrated with permanganate solution between 70 and 80 C. Even at this temperature, the hot oxalic acid solution decolorizes slowly at the beginning of the titration. The heating of solutions containing an excess of permanganate should be avoided because of the catalyzed d

39、ecomposition of permanganate. However, titrating hot oxalic acid directly with KMnO4 is acceptable because at no time during the titration is the oxidant concentration large. FORD LABORATORY TEST METHOD AK 103-02 Page 8 of 8 Copyright 2001, Ford Global Technologies, Inc. Ferrous Sulfate, Standard 0.

40、1 N A. Preparation Weigh out 28 g of reagent grade ferrous sulfate (FeSO4 7 H2O, formula weight = 278.05) and dissolve in a cooled mixture of 900 mL of distilled water and 100 mL of sulfuric acid (H2SO4). B. General Information The oxidation of Fe2+ to Fe3+ involves the production of one mole of ele

41、ctrons per mole of FeSO4. Therefore, the equivalent weight of the reagent, FeSO4 7 H2O, is equal to the formula weight and the normality (equivalents/liter) is equal to the molar concentration (moles/liter). Standardization of 0.1 N Ferrous Sulfate A. Procedure Take 40 mL of ferrous sulfate solution

42、 in an Erlenmeyer flask. Titrate at room temperature with 0.1 N potassium permanganate solution with constant agitation. Add the permanganate solution rapidly for at least three-quarters of the titration. Then add the permanganate slowly, allowing the color to fade after each addition until finally

43、a permanent faint pink color persists. Calculate the normality of the ferrous sulfate solution. B. General Information Ferrous sulfate can be standardized with potassium permanganate. 10 FeSO4 + 2 KMnO4 + 8 H2SO4 5 Fe2 (SO4)3 + K2SO4 + 2 MnSO4 + 8 H2O Solutions of ferrous sulfate are not stable sinc

44、e Fe2+ is easily oxidized to Fe3+. The prepared solution must be standardized prior to use for any determination. Chemicals, materials, parts, and equipment referenced in this document must be used and handled properly. Each party is responsible for determining proper use and handling in its facilities.