Determination of Sodium Monoxide in Sodium - Advances in

CHEMICAL SOCIETY. Peer Reviewed Book Chapter ... The purge gas is passed over hot titanium sponge for removal of oxygen. Error in transfer of solu...
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Determination of Sodium Monoxide in Sodium V. L. HANSLEY

and R. A.

KOLBESON

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

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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.

ADVANCES

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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

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

HANSLEY A N D KOLBESON—SODIUM

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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.

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4

Figure 2.

Amalgamation apparatus

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

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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.

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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

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

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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.

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

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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

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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)

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