Optical Absorbance in Nitric AcidNitrogen Dioxide-Water System S. LYNN, D. & MASON, I. AND B. H. SAGE Calgormia Institute of Technology, Pasadena, Calif.
T
the glass cap. A three-junction, copper-conatantan thermocouple for determining the Cemperature of the contents of the cell was mounted within the stirrer. The electromotive force from the thermocouple was measured by means of a potentiometer with a sensitivity of 1Opv. The temperature of the contents of the tranemission cell was known to be a t 32' F. within a probable error of 0.1' F. A glase piston-cylinder combination mounted on a nlicrometer screw was employed for the separate introduction of nitrogen dioxide and water to the nitric acid. The injector was maintained a t the ice point by circulation of alcohol through a glass jacket. Calibration of the injector with mercury indicated that the nitrogen dioxide was added with B probable error of less than 1 X 10-5 pound, which corresponded to an uncertainty of 0.5% of the weight of nitrogen dioxide added. In the case of mixtures containing small quantities of nitrogen dioxide a dilute solution of 0.03 weight fraction nitrogen dioxide in nithc acid was prepared and used in the glass piston-cylinder combination to make up these samples. This procedure permitted the small quantity of nitrogen dioxide to be established within 1% of the quantity added. Duplicate measurements were often made and no difficulty was experienced in obtaining a reproducibility of absorbance corrcEponding to 0.001 weight fraction nitrogen dioxide throughout the range of compositions investigated.
HE analysis of the liquid phase of mixtures of nitric acid, nitrogen dioxide, and water is of importance to industry. T h e optical absorbance of this phase appears to afford a means of estimating the quantity of nitrogen dioxide without the need for employing chemical techniques. Only limited studies of the optical absorbanee of the nitric acid-nitrogen dioxide-water system have been made. Hall and Blacet (6) established the abporption spectra of nitrogen dioxide, and Dalmon and Freymann (3)the absorbance of the nitric acid-water system at wave lengths Erom 950 to 1050 mp. White (9) recorded the use of infrared absorption in predicting the composition of commercial samplea of fuming nitric acid.
MATERIALS
The nitric acid was prepared in accordance with the procedures described by Giauque ( 4 ) which involved vacuum distillation of the acid from a mixture of recrystallized potassium nitrate and concentrated sulfuric acid a t a temperature of a poximately 100" F. Titration of a diluted sample with a stan&rdized solution of sodium hydroxide indicated that the acid as prepared contained less than 0.001 weight fraction of material other than nitric acid. Until ready for use the acid was stored a t a temperaturc below 0" F. after collection a t liquid air temperatures. Figure 1. Transmission Cell and
Thermocouple
Stirrer with
A n a result of the limited background of experimental data, measurements of the optical absorbance of the nitric acid-nitrogen dioxide-water system were ma.de a t atmospheric pressure and 32' F. for wave lengths of 425 and 500 mN. The studies a t 425 mp were limited to compositions containing a maximum of 0.008 weight fraction nitrogen dioxide and 0.007 weight fraction water and a minimum of 0.986 weight fraction nitric acid. Throughout this discussion the term "nitrogen dioxide" is used to designate equilibrium mixtures of nitrogen dioxide and nitrogen tetroxide. At 500 mp measurements were carried out for compositions containing a minimum of 0.70 weight fraction nitric acid. For present purposes optical absorbance is defined by the equation
A
=
-10g(I/1~)
(1) WAVE
In this equation A is the optical absorbance, Z is the intensity of light transmitted through the sample, and I , is the intensity of light transmitted through the cell filled with dry air. METHODS AND EQUIPMENT
The optical absorbance was measured with a Beckman D U spectrophotometer ( 1 , 6 ) that was modified so that the t,ransmission cell could be maintained a t 32" F. by immersion in an ice bath. Figure 1 is a photograph of the glass transmission cell and stirrer. The stirrer entered the cell through small holes in
LENGTH
m)l
Figure 2. Semiquantitative Effect of Wave Length on Absorbance of Mixtures of Nitric Acid and Nitrogen Dioxide a t 32' F.
Nitrogen dioxide was obtained from the Allied Chemical and Dye Corp. and was fractionated in a glass column provided with 16 plates. The central 707 of the overhead was collected over phosphorus pentoxide and stored in a atainless eteel vessel. Samples of nitrogen dioxide prepared in a similar manner from the same stock yielded less than 0.2 pound per square
1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
1954
Vol. 46, No. 9
~~~
TABLE I. XBSORBAZrCE
AT
500 h1.u FOR
.kCID-xITROGEU
SITRIC
Absorbance -log (I/I0j] 0 00 0 0,050 0.100 0.150 0,200 0 300 0,400
0.500 0,600 0,700 0.800 0,900 1.000 I . 100 1 200 1 300 1 400 1.500 1 600 1,700 1 800
0 0.0155 0.0300 0.0631 0 0556 0 0777
0 0100
0
0.0171 0.0315 0.0443 0.05% 0.0768 0.0976 0.0832 0 1129 0.1161 0 1332 0 1293 0,1446 0.1190 0 1641 0 1592 0.1728 0.1782 0.1'319 0.1860 0.1982 0.2045 0 209Y 0.2105 0 . 2 2 8 3 0.2211 0.2317 0 2393 o.25ni 0 . 2 4 2 5 0,2G07 0 , 2 5 2 7 0.2621 0 2708 0.2809 0 2718
0 0200
0 0.0182 0 0325 0 04.53 0.0539 0.0753 0.0928 0,1994 0 1251 0 1398 O.lj40 0 lU72 0 1799 0 1919 0 2032 0 2130 0 2244 0.2349 0.2447 0 2537 0 2630
NITRIC
0 0300 0 0.0186 0.0328 0 0449 0 0550 0 0739 0 0802 0 1063 0 1213 0 1356 0 1492 0 1820 0 1743 0 1859 0 1989 0 2080 0 2178 0 2281 0 2376 0 2462 0 2556
0 0400 0 0.0181 0.0322 0 0-136 0.0537 0.0718 0.0880 0.1032 0.1178 0 1314 0.1418 0.1571 0,1690 0,1804 0 1910 0.2007 0.2118 0.2217 0.2310 0,2399 0.2490
_________~_ ____
0 0500 0 0000 0 0700 0 0800 .Weight Fiaction h i t r o g e n Dioxide
0 0900
0 0.0171 0 0308 0.0413 0 0.516 0.06S1 0.0851 0.1000 0 1140 0.1276 0,1403 0.1524 0 . 1R41 0.1752
0 0.0120 0.0231 0.0325 0.0410
0.1858
0 1961 0.2062 0.2159 0 2254 0.2847 0,2438
ACID
0 0.0158 0.0291 0.0392 0.0491 0.0662 0,0822
0.0968 0,1106 0.1239 0.1363 0.1480 0.1595 0.1704 0.1809 0.1919 0,2012 0.2107 0.2205 0.2300 0.2394
0 0.0146 0.0274 0 0371 0.0470 0 0638 0.0781 0,0938 0 1071 0 1203 0 1326 0 1439 0 1551 0.1660 0 1764 0,1867 0.1968 0.2061 0,2162 0 2260 0 2352
0 0.0131 0 0252 0.0317 0.0443 0.0607 0,0729 0 0905 0.1037 0 1167 0.1288 0.1398 0.1510 0.1618 0.1722 0.1827 0.1925 0.2018 0.2121 0.2221 0.2316
(-1024
O.Ot570 0.0729 0,0874 0.1005 0 1131 0.1230 0,1370 0,1470 0 1577 0.1682 0.1780 0 1883 0 1981 0 2081 0.2185 0,2279
inch change in vapor pressure with a change in fraction in the gas phase from 0.02 to 0.5 a t a temperature of 160' F. Deaerated distilled water mas taken from the laboratory supply and was not further purified.
0 1200
0 0.0109 0.0211 0.0303 0.0392 0.0551 0.0698 0.0841 0.0971
0.1096
0.1224 0.13% 0.1433 0.1539 0.1646 0.1750 0.1850
0 1946 0 2018 0 2149 0 2243
0 1300
____ 0 0,0099 0.0191 0.0282 0 0369 0.0521 0.0666 0.0811 0,0938 0,1069 0.1170 0 . I280 0.13'56 0,1504 0.1699 0.1713 0.1812 0.1919 0 2008 0 2114 0 2210
0 0.0092 0 0174 0,0263 0.0348 0.0493 0 0637 0,077S 0 0903 0 1024 0.1141 0 1253 0 1301 0.1468 0.1572 0.1677 0 . 1777 0.1896 0.1973 0.2079 0.2174
*kBSORB.iNCE A T 425 >Ip FOR XITRIC L%CID-XITROGEN DIOXIDE-~~'.4TER SYSTEM AT 32" F.
___ K e i g h t Fraction Katcr---0.00 0,00300 0.00600 Weight Fyaction Kitrogen Uioxido n n n ;. 00093 6.00102 0.00185 0.00204 0,00277 0,0030ii 0.00369 0,0040G 0,00462 0.00607 0.0055? 0,00604 0.00647 0.00706 0,00741 0.00743 0.00801 0,00842
(I/,Iojl
n
500 M p
0 1100
__
hlearbance,
Effect of Composition on Absorbance at
0 1000
of the weight fraction of water for a wave length of 500 mp. Similar information is presented in Table I1 for studies a t a wave length of 425 mp. Figure 3 presents the results obtained for the ternary system a t a wave length of 500 mM and a temperature of 32" F. Variations in the weight fraction of water exert only a small effect on the absorbance particularly at low weight fractions of nitrogen dioxide. The behavior of the ternary system is shown in a somewhat different fashion in Figure 4, which illuatrates the effect of nitrogen dioxide on the absorbance for constant weight fractione of water. This behavior is relatively simple except a t sniall weight, fractions of nitrogen dioxide where the effect of lrater on the absorbance becomes more complicated. Similar information is presented in Figure 5 for the absorbance a t 425 mp. A t this wave length an increase in the weight fract,ion
T-IBLE11.
Figure 3.
32" F.
DIOXIDE--\ylTER SYSTEM A T
'&eight Fraction Watei
6,200
0 *on
0.600 0.800 i.ono 1.200 1 100 1,600
RESULTS
Exppioratory measurements of the absorbance of mixtures of nitric acid and nitrogen dioxide as a function of wave length were made in older to ascertain the most appropriate frequencies to employ in the detailed investigation. The results of these preliminary investigations are shown in Figure 2. For a system of constant composition the absorbance decreases rapidly with an increase in wave length. On the ba4s of the data presented in Wis figuie, wave lengths of 425 and 500 m p u-ere selected for the btudy. At these n'ave lengths the absorbance could be reproduced n i t h the spectrophotometer a i t h a probable error of lcss than 0.2570 The detailed experimental measurements a t 426 and 600 mp are available elsenhere ( 7 ) These data vere smoothed with respect to composition. In Table I the weight fraction of nitrogen dioxide is reported for even values of the absorbance as a function
004
008 WEIGHT
Figure 4.
012
016
FRACTIOY
020
NlTROGE'\.
024
028
3 CX13E
ibsorbance of Nitric Acid-Nitrogen DioxideWater System at 500 M p
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1954
electrical conductivity measurements ( 8 ) . A combination of the absorbance and electrical conductance affords a means of estimating the composition without t h e need of dilution except for ranges of composition where the same absorbance and electrical conductance were not obtained for two different compositions. Figure 7 depicts the interrelation of electrical specific conductance (8) and absorbance a t a wave length of 500 mfi. The relatively simple relationship of absorbance to the weight fraction of nitrogen dioxide makes this intensive property particularly useful in determining the quantity of this compound in fuming nitric acid.
1.6
w
9 2 0 2
1955
1.2
0.8
4
0.4 NITRIC ACID
Figure 5 .
Absorbance of Nitric Acid-Nitrogen Dioxide-Water a t 425 Mp
of water decreased the absorbance] as was the case at small weight fractions of nitrogen dioxide with a wave length of 500 mp. As a matter of interest, the behavior at the latter wave length a t zero weight fraction water has been included in Figure 5. A limited number of measurements a t 425 mp of the absorbance for the nitric acid-nitrogen dioxide-potassium nitrate system were made. The detailed experimental results are available (?), and the smoothed data are presented in Table 111. The effect of potassium nitrate on the absorbance of this ternary system is shown in Figure 6. In this instance an increase in weight fraction of potassium nitrate increased the absorbance for a fixed weight fraction of nitrogen dioxide. POSSIBLE METHOD OF ANALYSIS
Dilution techniques were employed in determining the composition of the nitric acid-nitrogen dioxide-water system from
TABLE 111. ABSORBAKCE AT 425 h4p FOR NITRICACID-NITROGEN DIOXIDE-POTASSIUII
NITRATE SYSTEM AT 32' F. Keight Fraction Potasslum Xitiate
Absoihance, [--log
umi
0 02000
0 04000
Weight Fraction Nitrogen Dioxide 0 0 0.00058 0.00072 0.00120 0.00144 0.00185 0.00216 0,00244 0,00292 0.00365 0.00310 0.00373 0.00440 0,00433 0.00811 0,00495 0,00583
0 0,200 0.400 0,600 0.800 1,000 1.200 1.400 1.600
1.6
Yz m
d
0
:0.6 0.4
WEIGHT
FRACTION
NITROGEN DIOXIDE
Figure 6. Absorbance of the Nitric Acid-Nitrogen Dioxide-Potassium Nitrate System a t 425 M p
Figure 7. Effect of Composition on Absorbance and Specific Conductance of Nitric Acid-Nitrogen D i o x i d e Water System ACKNOWLEDGMENT
This paper presents the results of one part of a research carried out for the J e t Propulsion Laboratory, California Institute of Technology, under Contract No. W-64-200 ORD-455 sponsored by the U. S. Army Ordnance Department. W. Ii. Lacey reviewed the manuscript. LITERATURE CITED
(1) Cary, H. H., and Beckman, A. O., J . Opt. SOC.Am., 31, 682-9
(1941). (2) Clark, J., Department of Defense, Research and Development Board, Washington, D. C., Symposium on Analysis of A-itric Acids, pp. 65-81, Dee. 31, 1951. (3) Dalmon, R., and Freymann, R., Compt. rend., 211,472-4 (19409, (4) Forsythe, W. R., and Giauque, W. F., J . Am. Chem. Sac., 64, 48-61 (1942). (5) Gibson, K. S., and Balcolm, M. M.,Research Paper 1798, J. Research Nut. Bur. Standards, 38, 610-16 (1947). (6) Hall, T. C., and Blacet, F. E., J . Chem. Phus., 20, 1745-9 (1952). (7) Lynn, S.,Mason, D. M., and Sage, B. H., Washington, D. C., Am. Doc. Inst., Doc. No. 4313 (1953). (8) Robertson, G. D., Jr., Mason, D. M., and Sage, B. H., IND. ENG.CHEY.,44, 2928-30 (1952). (9) White, L., Jr., Department of Defense, Research and Develop ment Board, Washington, D. C., Symposium on Analysis of Nitric Acids, pp. 43-53, Dec. 31, 1951. RECEIVED for review January 1, 1954. ACCEPTED April 10, 1954. A more detailed form of this paper (or extended version, or material supplementary to this article) has been deposited as Document No. 4313 with t h e AD1 Auxiliary Publications Project: Photoduplication Service, Library of Congress, Washington 25, D. C. A copy may be aeoured by citing the document number and b y remitting $1.25 for photoprints or $1.25 for 35-mm. microfilm. Advance payment is required. Make checks or money orderr, payable to Chief, Photoduplication Service, Library of Congress.
