Determination of Nitrate in Sodium Nitrite C . L. JOHNSON' Eastern Laboratory, E . I . dic Pont de Nemoiirs & Co., Inc., Gibbstown, IV. J . OWMAS
and Scott ( 1 )determined nitrate by pipetting a sample
lyas excluded, Reaction 2 could be reversed. The end result xould he the quantitative conversion of the nitrite originally present to nitrososulfuric acid arcording to Reaction 3. The nitrate crould then be titrated n i t h iron(I1) sulfatr nithout inteifeiencr from nitrite or nitrososulfuric acid. The required conditions 11 ere realized by adding an aqueous solution of the sample to caolci, roncentrated sulfuric acid in a n evacuated bottle.
13 under the surface of concentrated sulfuric acid and titrating the nitrate nith standard ironfII) sulfate solution: HSO?
+ 2FeSO4 + 2H2S04 =
HSOSO,
+ Fc?(SOa)Z+ 2H2O
(1)
This method is rapid and convenient. Although Boir-man and Scott stated that nitrite does not interfere, their data indicated increasing positive errors with increasing contents of nitrite. This error is due mainly to the formation of nitrate from nitrite, which always occurs to some extent TI hen a solution of nitrite is strongly acidified: 3HXO2
HSOa
+ 2x0 + H?O
(2)
I n this laboratory, it has been found possible to use the Bowman and Scott method for the determination of nitrate in sodium nitrite solutions by using a fine-tipped pipet to provide a slow addition of the solution to cold, rapidly stirred sulfuric acid, and applying a n empirical correction depending on the amount of nitrite present. Such empirical corrections hold only over relatively restricted ranges of nitrate and nitrite concentrations and require strict adherence to prescribed conditions. At low concentrations of nitrate, the correction may be larger than the amount of nitrate determined. A method free from these disadvantages of the Bowman and Scott procedure was desired. A modification of the method of Fischer and Steinbach (Z), in which nitrate was determined by the BowmaniScott titration after separation of nitrite as the volatile methyl ester, had been found applicable to the analysis of r e l a t i v e l y pure sodium nitrite salt. H o m v e r , errors became excessive a t nitrate concentrations above 15%, and the method was considered inapplicable in the analysis of solutions containing r e l a t i v e l y l a r g e a m o u n t s of nitrate. U b a l d i n i a n d Guerrieri (6) modified Figure 1. Reaction Yessel the procedure of Fischer and Steinbach by extracting the methyl nitrite with a solvent. This modification did not seem likely to overcome the deficiencies of the modified Fischer-Steinbach method. Other methods involving the preliminary destruction or separation of nitrite ( 4 ) were considered, but none appeared t o be as rapid, convenient, reliable, or generally applicable as n simple modification of the method of Bowman and Scott. I n this method, the bulk of the nitrite is converted to nitrososulfuric acid:
HSOz
+ H2SOa = IlNOSO4 + H2O
(3)
It is only as a result of high local concentrations of nitrite that Reaction 2 occurs. It seemed probable t h a t if the products of Reaction 2 could be retained in the reaction vessel n-hile oxygen 1 Present addrers, Burnside Laboratory, E. I Co., Inc., Penns Grove, 1- J
du Pont de XPrnoiir? 8:
PROCEDURE
Place 150 ml of cold (0' to 10" C.) concentrated sulfuric acid in a standard 500-ml. borosilicate glass reagent bottle tested to withstand 2 atmosphrres of external pressure (Figure 1) For additional safrty, the bottle should be enclosed in a suitahlc cover. Insert the funnel assembly and evacuate the bottle through the side arm n i t h a good vacuum pump for 3 minutes, snirling the acid to aid in the removal of dissolved air. Closr, the stopcock on the side arm and disconnect the bottle from t h r vacuum pump. For the analysis of sodium nitrite solutions, 1%-eigha 5- to 10ml. sample into a small glass-stoppered weighing bottle and transfer it to the funnel. For the analysis of sodium nitrite salt, weigh a 5-gram sample into a 30-ml. beaker. dissolve in 10 ml. of water, and transfer to the funnel. K i t h the bottle partlj- immersed in ice water, introduce the sample in small portions by careful manipulation of the stopcock, with good agitation and cooling between additions. K a s h the sample container and funnel with three 3-ml. portions of water. Shake the bottle to rinse d o m any salt which may have crystallized out in the upper part of the assembly. Shake the bottle vigorously, preferably in a mechanical shaker, for 20 minutes. Transfer the contents of the bottle to a 400-ml. beaker, rinsing the bottle twice with 15- to 20-ml. portions of sulfuric acid by vigorous shaking with the funnrl assembly in place. Cool to 10" C. or Ion-er and titrate to the first pink coloration with standard 0.6 -Yiron(I1) sulfate solution (176.5 grams of ferrous sulfate heptahydrate and 400 ml. of water diluted to 1 liter n-ith 60% sulfuric arid) For the mopt accurate results, the temperature a t the r a n d point should not be higher than 10" C. A N 4 L Y S I S OF KYOWN SAMPLES
I n Table I are shown the results of analysis of known mixtures of potassium nitrate and sodium nitrite by this procedure. These salts were used hecnuse samples of k n o m high purity were available.
Table I.
KNOs Taken, Grams 0.0000 0.0055 0.0537 0.5033 0 5978 0.9474 1.2003 1.2051 1.1954 1.2072
Analysis of Known Mixtures of Potassium Nitrate and Sodium Nitrite
NaNOt Taken, Grams 5,000 5,226 5,077 4.5080 4.5012 2.9733 1.2018 0.1295 0.1104 0.0000
FeSOI (0.03048 Gram of KNOs/
Ml.), M1. 0.17 0.30 1.86 16.48 19.27 31.27 39.26 39.36 39.06 39.62
KXOI KSOI KNOz Found, Present, r o u n d , Grams % % 0.0052 0.00 0.10 0.11 0.17 0.0091 1.05 1.11 0.0567 10.04 10.02 0.5023 11.72 11.52 0.5873 0 9531 24.16 24.31 49.80 1 , 1 9 6 3 49.97 1.1997 90.30 89.89 1 , 1 9 0 5 91.55 91.17 1.2076 100.00 100.03
Error, %
+o. 10
4-0.06 + O . 06 -0.02 -0.20 + O . 15 -0.17 -0.41 -0.38 to.03
Shaking Time, Minutes 20 20 15 30 10 5 15 15 15 15
These results indicate an accuracy nithin =t0.10% in the range 0 to lo%, within +0.2070 in the range 10 to 50%, and \Tithin +0.4Y0 at 90% potassium nitrate. Under the conditions given, the final concentration of sulfuric acid is about 81% when the titer is 40 ml. According to Lunge ( 3 ) , nitrososulfuric acid is stable in sulfuric acid of more than 6570 strength. Since the iron(I1) sulfate solution is about 4670 sulfuric acid, the amount of sulfuric acid in the final titrated 1276
V O L U M E 25, NO. 8, A U G U S T 1 9 5 3 solution will not fall below 65% even with titers as large as 100 ml. INVESTIGATION OF END POINT
130\vman and Scott stated that many experiments indicated that an excess of 0.2 ml. of 0.63 S iron(I1) sulfate solution is requircd to produce the end point in a volume of 100 to 150 ml. 1:rpcriments were made to check this point.
.I solution cont:iining 0.0012 grams of potassium nitrate per nil. \vas prrpareti. One milliliter of this solution was calculat,ed equivalent to 0.04 ml. (1 drop) of the iron(I1) sulfate solut!) tion. Onr hundrcd-milliliter portions of cold sulfuric acid were : ~ l d c dto I-ml. portion3 of the potassium nitrate solution. Various amounts of water were added, and the solutions were titrated at various tempt.rature3, with the results shown in Table 11. The titrations art. corrected for the 0.04 ml. of iron(I1) sulfate solution consumed by t>hepotassium nitrate added. 1118
The results indicate that, under suitable conditions of acid conc-cntration and temperature, the end point is produced by the firpt drop of excess reagent. Under such conditions, no blank should hr deducted. The concentration of acid appears to be the n i o i ~important fact,or. When no n-ater \vas added other than t h a t i i i the potasPiuni nitrate solution (so that the acid concentration :it thr tlnd point was 95 t o 96a/0), 0.14 to 0.21 nil. of excess iroti(I1) su1i':itc solution \vas requirrtl to produce the end point, Xvith more required at 23" C. than a t 7 " C. In t h c s t(ssts in which 10 to 21 i d . of witcr \vas added to give acid roncentrations of 86 to 111yo,thr rntl point x i s produced hy thct first drop of excess iroii(I1) sri1f:itr solution :it temperatures below 10" C. When the :ic,itl conc*rntr:itiou\vas about 91 :ind the temperature 23" C., 2 ( I r o p ~(0.07 nil.) ot' c x c e s iron( 11) sulfate wlution were required t o l~roduc*c~ thcl end point. I t \vas concluded that when t,he arid a t the end point is 86 to 9170 and the titration is c~ciiic~c~iit~:itiori
1277 Table 11. Excess of 0.6 X Iron(I1) Sulfate Solution Required for End Point under Various Conditions \I-ater added, ml. H80a solution,
it
0 95 23 0.21
'$6
Tcmp., C. I'cS0a for end point, nil.
n
93 7
0.14
9 Yl 23 0.07
9 91 6 0.03
20 86 6 0.04
conducted, or a t least finished, a t a tem#erature no higher than 10" C., no blank should be deducted from the iron(I1) sulfate titration. hlthough a positive error of 0.10% \vas found at 0 % potassium nitiate (Table I), other results in Table I indicate that deduction of a blank would impair the results when substantial amounts of nitrate are present. Examination of Reaction 2 suggests that prolonged shaking may be required to effect complete reversal of the reaction at very low roncentrations of nitrate. A shorter shaking period should suffice in the presence of substantial concentrations of nitrate. The specified 20-minute shaking time was chosen to provide a reasonably long time for reversal of Reaction 2 n ithout prolonging the determination. LITER-ITURE CITED
(1) Uowniaii, F. C., and Scott, IT. W., J . Irid. Eng. Chcm., 7, i 6 G (1915). ( 2 ) Fischer. W. M., and Steinbach, S . , Z. artorg. Cliern., 78, 134 (1912). ( 3 ) Lunge, George, "The LIanufactiire of Sulfuric .icid and .ilkali," 4th ed., Vnl. I , Part I, p. 339, Xew York, D . 1-an Xostrand Cn., 1913.
Seaman, W., S o r t o i i , .I.R., Mader, IT. J., and Hugorlet, J. J.. Isn. E s r ; . ('HEM., .\SAL. ED., 14, 420 (1042). ( 5 ) I.-lialdiiii, I.. and Guerrieri, F., -4rin. c h i m . ~ j ? p Z . ,38, i o 2 (1948). (4)
1IEcPIi.t.D
f o r review January 22, 1933.
Accepted May 23, 1953
7 1. Salicylamide (0-Hydroxybenzamide) Contributed b j W iLTEH C. MCCRONE 4YD H iLl'11 J . IIINCII, J R . , Armour Hesearch Foundation of Illinois Institute of Technology, Chicago 16, Ill. S - R . k Y 1 ) I F F R S C T I O I D.4T.I
u-OH Structural Formula for Salicylamide
('cll Dimensions. a = 12.93 A , , b = 5.02 A , , c = 24.80 i 0.2 .I. Formula IVeights per Cell. 8 (8.05 calculated from x-raxdata).
Firmula \\-eight. 137.13. Density. 1.320 (flotation and pycnometer) : 1.308 (x-ray).
Principal Lines is soluble in chloroform, ether. and alcohol, slightly soluble in water, and insoluble in benzene, carbon trtrachloritle, and xylene. It can be crystallized from ethyl alcohol (Figure 1) or he sublimed to give flat crystal plates. There is a polymorphic form obtained in fusion preparations. S.ycYL.mmE
MORPHOLOGY Crystal System. llonoclinic. Form and Habit. Rods from solvents or sublimation elongated parallel to 6 and showing the clinopinacoid ( O l O ) , ort,hopinaroid 1 100 1, basalpinacoid ( 001 } , and orthodomal prism { 1071. Axial Ratio. a:b:c = 2.576 : l-: 4.940. Inkrfacial Angles (Polar). lOlh100 = 23"; 100A001 = F3". ( 'RYBTAI.
0011101 = 940. Beta Angles. 117'
Cleavage.
Excellent parallel to b.
d 10.52 6.46
6.03 5.49 5.22 4.84 4.6.5 4.42 4.24 4.09 3.83
1/11 0.43 0.48 0.04
0.72 0.30 0.41 0.09
n 04 0.29 n 09 0.07
d 3.48 3.31 3.21 3.06 2.78 2.69 2.63 2.41 2.32 2.25 2.15
1/11 1.00 0.06 0.60 0.04 0.38
0 13 0.02 0 . 16 0.04 0.07 0.09
d 2.11 1.936 1.889 1.830 I . 780 1.747 1,703 1.632 1 607 1 549
1/11 0 09 n 05 0 06 o 06 o 04 0 03 0 OB 0 0.5 0 06 0 04
OPTIC.4L PROPERTIES
Refractive Indices (6893 -4.. 25' C.). LY = 1.595 f 0.002. = 1.63'7 f 0.001. y = 1.727 + 0.005. Optir Axial Angles (6893 &4., 25' (3.). 2H = (+)82.5". 27' = (+);So (calculated from p and 2 H ) , 2V = 75" (calculated from CY, ps and 7 ) . Dispersion. r > v , very strong. Optic Axial Plane. 010.
