Determination of Sodium Monoxide in Sodium - Advances in

Determination of Sodium Monoxide in Sodium V. L. HANSLEY

and R. A.

KOLBESON

Research Division, U.S. Industrial Chemicals Co.,

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on June 2, 2015 | http://pubs.acs.org Publication Date: January 1, 1957 | doi: 10.1021/ba-1957-0019.ch017

Cincinnati 37, Ohio

A modification of the amalgam procedure for the determination of oxygen in sodium provides a high degree of accuracy. The argon atmosphere chamber for preliminary handling is replaced by dry, heavy oil. Actual sampling is p e r f o r m e d through a No. 1 Greenerd Arbor sodium press, which injects the sodium into the amalgam extraction tube as a 3/32-inch wire. The purge gas is passed over hot titanium sponge for removal of oxygen. Error in transfer of solution is eliminated by titrating the isolated oxide in place.

T H E entrance of s o d i u m into a series of n e w applications i n recent years has necessitated the development of a n a l y t i c a l methods for d e t e r m i n i n g trace i m p u r i ties such as oxygen, nitrogen, h y d r o g e n , a n d carbon. A t o m i c energy applications have developed some i n f o r m a t i o n , p a r t i c u l a r l y o n a n a n a l y t i c a l procedure for oxygen. A modification of the P e p k o w i t z a n d J u d d (1,2) m e t h o d for the determination of s o d i u m m o n o x i d e i n s o d i u m applies to sample p r e p a r a t i o n a n d apparatus, w h i l e the p r i n c i p l e of the method remains the same. T h e procedure is based o n the i n s o l u b i l i t y of s o d i u m m o n o x i d e i n the a m a l g a m f o r m e d b y a s o d i u m sample w i t h m e r c u r y a n d the density of the m o n o x i d e as c o m p a r e d to the a m a l g a m . T h e m o n o x i d e floats o n the surface of the a m a l g a m , a l l o w i n g separation f r o m the a m a l g a m b y several washings w i t h m e r c u r y . T h e weights of the s o d i u m sample a n d the oxide are d e t e r m i n e d b y titration of the a m a l g a m a n d the oxide i n solution, respectively. T h e s a m p l i n g technique has been so modified that a n argon atmosphere c h a m ber is e l i m i n a t e d a n d the p r e l i m i n a r y s o d i u m h a n d l i n g is done u n d e r h e a v y o i l . T h e s o d i u m is actually sampled t h r o u g h a N o . 1 G r e e n e r d A r b o r s o d i u m press w h i c h injects the s o d i u m into the a m a l g a m extraction tube as a 3 / 3 2 - i n c h w i r e . A rigorous argon p u r i f y i n g t r a i n u t i l i z i n g hot t i t a n i u m sponge is added. F i n a l titration of the isolated oxide is p e r f o r m e d i n place i n the a m a l g a m extraction tube. W i t h these modifications, procedures a n d apparatus are such that d e t e r m i n ations c a n be r u n b y a n average analyst, without specialized s k i l l , a n d w i t h a h i g h degree of accuracy. Apparatus T h e a r g o n - p u r i f y i n g system is s h o w n i n F i g u r e 1. A represents the source of gas w h i c h flows t h r o u g h tube D containing the t i t a n i u m sponge. D , constructed of Inconel m e t a l l ^ inches i n inside diameter, measures 18 inches to the Teflon gasket of the flange fitting. A b o v e the Inconel section is a stainless steel p a c k i n g 1

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In HANDLING AND USES OF THE ALKALI METALS; Advances in Chemistry; American Chemical Society: Washington, DC, 1957.

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IN CHEMISTRY SERIES

Figure 1. Argon purifier

g l a n d w i t h a n inside diameter of 1*4 inches a n d 3V4 inches long, w i t h a brass p a c k i n g g l a n d nut. A stainless steel p i p e runs the l e n g t h of the connected Inconel a n d stainless steel outer sections. T h i s pipe has a n 8 - i n c h u p p e r section V2 i n c h i n i n side diameter; the l o w e r section has a n inside diameter of 3/16 i n c h . T h e pipe also has several perforations at its e n d f o r gas entrance. T h e Inconel tube is filled to a depth of a p p r o x i m a t e l y 9 inches w i t h 8 to 20 m e s h t i t a n i u m sponge. Ε represents a pressure release consisting of a m e r c u r y t r a p w i t h the i n n e r tube i m m e r s e d so that t i t a n i u m purification tubes c a n be evacuated without d r a w i n g m e r c u r y out of the tube a n d into the p u m p or system. Β represents the source of heat capable of m a i n t a i n i n g 800 ° C . T h e heating c e l l is 9 inches i n d e p t h a n d 4 inches i n w i d t h . T h e furnace is a H o s k i n s T y p e F D 2020, 110 volts, 11.8 amperes. C represents the t h e r mocouple l e a d i n g to a P y r o - V a n e h i g h l i m i t cutoff thermoregulator f r o m the W h e e l c o Instrument C o . F i g u r e 2 represents the a m a l g a m a t i o n apparatus. A is a standard s o d i u m press ( 3 / 3 2 - i n c h w i r e die) ( N o . 1 G r e e n e r d A r b o r Press, F i s h e r Scientific C o . , N e w Y o r k , N . Y . ) . T h e d i e - r e t a i n i n g n u t has been lengthened b y silver soldering of a stainless steel n i p p l e (V - i n c h i n outside diameter) to the n u t f o r attaching a brass 28/12 b a l l joint. T h e borosilicate glass adapter, Β ( t u b i n g Ms-inch i n outside diameter w i t h 28/12 socket joint 21/2 inches l o n g f r o m joint to 1 0 - m m . stopcock), is c o m p r i s e d of a side a r m for the k n i f e , a 1 0 - m m . stopcock, a side a r m for e v a c u ating a n d filling w i t h argon, a n d a s p h e r i c a l connection joint. T h e s o d i u m cutting knife, C , is operated t h r o u g h a close-fitting pressure t u b i n g . 2

A s m a l l indentation cutting b l o c k is made i n the borosilicate glass t u b i n g opposite the opening for the cutter. T h e k n i f e is soldered to a 1/16 χ 6 ^ - i n c h brass rod. T h e side a r m f r o m adapter B , s/ -inch i n outside diameter a n d IY2 inches long, is r e d u c e d to a n outside diameter of V4-ineh w i t h a m e t a l r e d u c i n g v a l v e . A smaller v a c u u m t u b i n g (3*£ inches long) is attached to the 14-inch e n d of r e d u c e r a n d h a n d l e e n d of the brass r o d . A l l attachments of r u b b e r t u b i n g to glass a n d copper are w i r e - t i e d . D is a n i n n e r seal at the bottom of the adapter to prevent s o d i u m f r o m c o m i n g i n contact w i t h a n y stopcock grease. A 1 0 - m m . stopcock is 8


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i m m e d i a t e l y b e l o w this joint. T u b e Ε is used for r e c e i v i n g a s m a l l length of s o d i u m w i r e w h i c h cleans the die. T h i s tube is replaced w i t h analysis tube F after the f i r s t - r u n w i r e has been cut a n d the stopcock o n Β closed. T h e analysis tube (iy inches i n inside diameter a n d 5 inches i n length) has two c a p i l l a r y side arms w h i c h are needed to conduct titrations i n this vessel. T h e standard solution is i n t r o d u c e d into one a r m , w h i l e the other acts as a " b r e a t h e r . " D u r i n g the amalgamation a n d extraction steps m e r c u r y is i n t r o d u c e d t h r o u g h one a r m w h i l e the other is closed w i t h a piece of r u b b e r t u b i n g a n d a screw c l a m p . G is a reservoir for cleaning m e r c u r y , made f r o m a 250-ml. p e a r - s h a p e d b u l b . A m e d i u m - g r a i n fritted-glass filter is sealed into the bottom of the b u l b for a final cleaning of the m e r c u r y . In operation the filter is always kept covered w i t h m e r c u r y , w h i c h allows n i t r o g e n pressure to be used to force the m e r c u r y t h r o u g h the filter. T h e n i t r o g e n pressure regulator, H , is set at 10 pounds p e r square i n c h o n the l o w side of the pressure regulator to p r o v i d e constant pressure o n the m e r c u r y . T h e purified argon source, I, is s h o w n i n F i g u r e 2.


4

Figure 2.

Amalgamation apparatus


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T h e m e r c u r y - p u r i f y i n g system rs illustrated i n F i g u r e 3. T h e 500-ml. b o r o s i l i cate glass separatory f u n n e l has the t i p d r a w n out to a fine c a p i l l a r y to give a l o w m e r c u r y flow rate. Β leads f r o m a r e s e r v o i r of 1 % h y d r o c h l o r i c acid. T h e b o r o s i l i cate glass c o l u m n , C , is a p p r o x i m a t e l y 28 inches l o n g w i t h a n inside diameter of 1 i n c h , h a v i n g a n inlet at the bottom for dilute h y d r o c h l o r i c acid a n d a n outlet to d r a i n at the top. C o l u m n D has the same dimensions as C . A m e r c u r y seal at the bottom of each c o l u m n is effected b y the U - t u b e s . W a s h e d m e r c u r y is collected i n the borosilicate glass flask E. F represents the G l a s - C o l heating mantle for the 500-ml. borosilicate glass flask, G . T h e air condenser, H , is constructed of b o r o s i l i cate glass V2 i n c h i n inside diameter w i t h a l e n g t h of a p p r o x i m a t e l y 23 inches a n d a 24/40 Τ joint.


Reagents S t a n d a r d i z e d 0.5N h y d r o c h l o r i c a c i d solution S t a n d a r d i z e d 0.005IV h y d r o c h l o r i c acid solution S t a n d a r d i z e d 0.5N s o d i u m h y d r o x i d e solution 1% p h e n o l p h t h a l e i n solution Light naphtha (Skellysolve E ) 1 % h y d r o c h l o r i c acid solution

Procedure A l l parts of the a m a l g a m a t i o n apparatus must be t h o r o u g h l y cleaned a n d d r i e d . T h e s o d i u m sample is p r e p a r e d b y cutting a 2 - i n c h c y l i n d r i c a l piece f r o m a larger b r i c k of s o d i u m u n d e r heavy, d r y , inert m i n e r a l o i l w i t h a N o . 9 cork borer. T h e ends are t r i m m e d off w i t h a sharp putty knife a n d the sample is r i n s e d i n a series of three vessels containing d r y , light n a p h t h a . A f t e r a thorough r i n s i n g to r e m o v e a l l o i l , the sample is q u i c k l y inserted into the m o l d of the s o d i u m press, A ( F i g u r e 2 ) , w h i l e still coated w i t h a film of n a p h t h a . T h e upper part of the apparatus is sealed b y pressing a p p r o x i m a t e l y 2 inches of s o d i u m w i r e t h r o u g h the die. A few drops of h e a v y o i l placed at the top of the die a r o u n d the piston aids the sealing. A s m a l l tube, Ε ( F i g u r e 2 ) , is connected to the system at D for r e c e i v i n g the first cut of s o d i u m w i r e w h i c h is to be discarded. W i t h the stopcock o n Β open, the system is evacuated to b e l o w 25 microns w h i l e b e i n g flamed w i t h a B u n s e n b u r n e r . T h e system is then filled to a pressure of 25 c m . of m e r c u r y w i t h argon w h i c h has passed t h r o u g h the argon purifier ( F i g u r e 1) set at 800 °C. A f t e r p u r g i n g the system w i t h four successive evacuations a n d backfillings w i t h argon, a n additional 2 inches of s o d i u m is pressed w h i l e the system is u n d e r a 25-cm. p r e s sure. T h e total 4 inches is cut w i t h knife, C , a n d the stopcock o n Β is closed. T h e 4 - i n c h w i r e is discarded. T u b e F is p l a c e d at D ( F i g u r e 2 ) . T h e pressure t u b i n g leading f r o m the m e r c u r y reservoir to the lower c a p i l l a r y opening o n tube F is attached a n d the u p p e r c a p i l l a r y opening is closed w i t h a piece of r u b b e r t u b i n g a n d a p i n c h c l a m p . W i t h the stopcock opened o n tube F, the evacuation cycle is repeated three times a n d finally the system is filled to a n argon pressure of 5 c m . of m e r c u r y . A p p r o x i m a t e l y 20 m l . of m e r c u r y is admitted into tube F, using just sufficient pressure to force the m e r c u r y t h r o u g h the filter a n d into the tube. T h e stopcock o n Β is opened, and a sample of s o d i u m w i r e is pressed into the system u n t i l a length of 10 inches is obtained. ( T h e 3 / 1 6 - i n c h die i n the s o d i u m press w i l l produce a 10-inch length to w e i g h a p p r o x i m a t e l y 1 gram.) T h e s o d i u m w i r e is cut w i t h k n i f e C a n d d r o p p e d into the m e r c u r y . T h e reaction of s o d i u m w i t h m e r c u r y is vigorous even o n this scale. T h e heat developed necessitates the use of a safety screen between the operator a n d the apparatus for this step. T h e m e r c u r y extractions are started b y d r a w i n g off the o r i g i n a l a m a l g a m into a 500-ml. E r l e n m e y e r flask u n t i l the top surface of the c a p i l l a r y loop begins to show beneath the surface of the metal. T h e s o d i u m oxide, contained i n the s o d i u m sample a n d contaminated w i t h m e r c u r y , w i l l be floating as a dust o n the s m a l l amount of a m a l g a m r e m a i n i n g i n the extraction tube. A n o t h e r 10 to 15 m l . of m e r c u r y is i n t r o d u c e d a n d w a r m e d slightly w i t h a flame to facilitate the s o l u tion of a m a l g a m i n the n e w m e r c u r y . T h e extraction tube is s w i r l e d b y rotating



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10 V.

Figure 3. Mercury purifier

a r o u n d the b a l l joint, D . T h e a m a l g a m is a l l o w e d to stand for 3 to 4 minutes a n d then d r a i n e d into t h e 500-ml. E r l e n m e y e r flask just to the top of the c a p i l l a r y as before. T h e surface of m e r c u r y is n e v e r a l l o w e d to f a l l to the c a p i l l a r y o p e n i n g ; o t h e r wise some of the p o w d e r y oxide w h i c h floats o n the surface of the m e t a l w i l l be d r a w n into the c a p i l l a r y and apparent oxide analysis w i l l be too low. A total of four extractions is p e r f o r m e d i n this m a n n e r , after w h i c h the stopcock o n tube F is closed a n d the tube disconnected at D . W i t h the tube free the r e m a i n i n g e x t r a c tions are c a r r i e d out w i t h vigorous s h a k i n g . A total of 8 to 10 extractions u s u a l l y removes a l l of the a m a l g a m . H o w e v e r , extractions are continued u n t i l a sample of 2 to 3 m l . of m e r c u r y tests free of a l k a l i w h e n s h a k e n w i t h a f e w drops of p h e n o l p h t h a l e i n solution. A l l such test portions of m e r c u r y are added to the o r i g i n a l a m a l g a m i n the 500-ml. E r l e n m e y e r flask. T h e sample weight is accurately d e t e r m i n e d b y decomposing the a m a l g a m w i t h a measured excess of 0.5N h y d r o c h l o r i c acid. T h e m e r c u r y a n d aqueous solution are transferred to a separatory f u n n e l a n d shaken v i g o r o u s l y . T h e m e r c u r y is separated f r o m the aqueous l a y e r a n d the latter is r e t u r n e d to the 500-ml.


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flask, w h e r e it is b a c k - t i t r a t e d for r e s i d u a l h y d r o c h l o r i c acid w i t h 0.5N sodium h y d r o x i d e . T h e weight of s o d i u m sample is calculated f r o m the v o l u m e of 0.5N h y d r o c h l o r i c acid consumed. T h e amalgamation tube is r e m o v e d f r o m the apparatus a n d a p p r o x i m a t e l y 8 to 10 m l . of d i s t i l l e d water is i n t r o d u c e d t h r o u g h the lower c a p i l l a r y . T h i s water s h o u l d be freshly b o i l e d a n d neutralized to a p h e n o l p h t h a l e i n e n d point. T h e oxide i n solution is titrated w i t h 0.005N h y d r o c h l o r i c acid w i t h the tip of a m i c r o buret attached to the l o w e r c a p i l l a r y of tube F w h i l e the u p p e r c a p i l l a r y is used as a breather. G r a m s of sample = [ ( m l . of H C 1 χ Ν) - ( m l . of N a O H χ Κ) ] 23/1000


G r a m s of o x y g e n = m l . of H C 1 Χ Ν χ 8/1000 ^ grams of o x y g e n % oxygen = =— χ 100 grams of sample

Recovery of Oxygen K n o w n amounts of m e r c u r i c oxide were added to the a m a l g a m a t i o n tube, F , p r i o r to the addition of sodium. U p o n a m a l g a m a t i o n the tube was heated a n d v i g orously shaken for several minutes to b r i n g about the reaction of m e r c u r i c oxide a n d s o d i u m to produce s o d i u m monoxide. T a b l e I illustrates the recoveries of oxygen.

Table I. Recoveries of Oxygen from Sodium

0

Sample S o d i u m , No. Grams 1 2 3 4 5 6 a b

1.052 1.097 1.087 1.157 1.049 0.997

Oxygen Gram

Blank

0.0000728 0.0000618 0.0000635 0.0000804 0.0000492 0.0000804

0.00692 0.00554 0.00585 0.00694 0.00469 0.00806

%

Sodium, Grams 1.046 0.974 1.066 1.086 1.015 1.015

Oxygen Added, Gram 0.0000812 0.000133 0.000103 0.000251 0.000192 0.00162 b

Oxygen Gram

Found

0.000139 0.000107 0.000120 0.000254 0.000326 0.00163

0.0133 0.0109 0.0112 0.0233 0.0242 0.166

%

Blank and Theory. % 0.0146 0.0191 0.0152 0.0300 0.0235 0.167

T h e o r e t i c a l per cent and b l a n k per cent based on respective sample weights. E x t r a o x y g e n added as m e r c u r i c oxide.

Av.

Deviation

-0.0013 -0.0082 -0.0040 -0.0067 +0.0007 -0.001 0.0037

Discussion A s a l l joints are l u b r i c a t e d w i t h a h i g h - v a c u u m stopcock grease, the analyst must exercise extreme care i n p r e v e n t i n g the grease f r o m c o m i n g into contact w i t h the s o d i u m w i r e . If this happens, the grease later entraps the a m a l g a m a n d prevents its extraction w i t h m e r c u r y , l e a d i n g to h i g h results. P r o p e r l u b r i c a t i o n of stopcocks w i l l p r e v e n t this contamination. T h e m e r c u r y is recovered b y a n acid a n d water rinse using the apparatus s h o w n i n F i g u r e 3. T h e m e r c u r y is f e d t h r o u g h separatory f u n n e l A at a n a p p r o x i mate rate of 5 grams p e r m i n u t e . It receives a n acid w a s h i n c o l u m n C a n d a water w a s h i n c o l u m n D, w h i c h has water c o n t i n u a l l y r u n n i n g t h r o u g h it. T h e washed m e r c u r y is collected i n vessel E , f r o m w h i c h it is transferred to flask G , for d r y i n g u n d e r v a c u u m . C u r r e n t , controlled t h r o u g h a V a r i a c , is a p p l i e d u n t i l the m e r c u r y begins to reflux. T h e pot temperature w i l l be 140° to 160 ° C . A f t e r refluxing for 1 h o u r the m e r c u r y is cooled u n d e r v a c u u m a n d transferred to a clean, d r y stock bottle. T h e t i t a n i u m sponge i n the argon purifier reacts w i t h o x y g e n v e r y r a p i d l y . Consequently, the argon purifier s h o u l d be a l l o w e d to cool u n d e r a positive p r e s sure of a r g o n to prevent a n y air f r o m being d r a w n into the tube.

Literature Cited (1) (2)

P e p k o w i t z , L. P., J u d d , W . C., A n a l . Chem. 22, 1283 (1950). P e p k o w i t z , L. P., J u d d , W . C., D o w n e r , R. J., i b i d . , 26, 246 (1954)


Determination of Sodium Monoxide in Sodium - Advances in

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