ANALYTICAL EDITION
November 15, 1942
87 1
(3) Hummel, F. C., and Willard, H. H., Ibi,d., 10, 13 (1938).
The method is easily carried out and requires no longer, possibly little less, time than usual titrimetric methods. Very few diverse ions interfere with the color and a \\ride range in p H values is possible. An alternate procedure for reducing the iron ivith stannous chloride is not recommended.
{:;,:!$E $$'**(:izj. 79
27 (1935)*
Ibid., 9, 162 (1937); 136 (1938). (7) Saywell, L. G., and Cunningham, B. B., Ibid., 9,67 (1937).
ABSTRACTED from a thesis submitted bg- H . R . Hulett t o t h e Graduate School of Oregon State College in partial fulfillment of the requirements for the degree of master of science. Published with the approval of the Monographs Publication Committee, Oregon State College. Research paper No. 65, School of Science, D e p a r t m m t of Chemistry
Literature Cited (1) Blau, F., Monatsh., 19, 647 (1898). (2) Fortune, W. B., and bfellon, M G., 1x0. ESG.C H G U . . - 1 s ~ E D~. .. 10, 60 (1938).
Detection and Semiquantitative Estimation of Group I Cations S. S. LEIKIYD, R O B E R T JIAURAIEYER, AND hIILTON CUTLER, Rrookl!n College, Brooklyn, N. Y.
IK
THE classical procedure for the qualitative analysis of Group I (silver, lead, mercury), the chlorides are precipitated and the lead chloride is extracted with hot ~ ~ a t e r . The residue is then treated with aqueous ammonia to separate the silver from the mercury. Two valid objections to this procedure are: The extraction of lead chloride is complete only after many washings and hence is necessarily time-consuming. Silver ion in the presence of comparatively large amounts of mercury sometimes escapes detection (in the hands of a beginner) when ammonia IS added to separate the silver from the mercury. This is due to the reduction of silver ion to metallic silver by the mercury formed as a result of the reaction between mercurous chloride and ammonia. Small amounts of silver may thus escape detection due t o their absence in the ammonia extract. Of course, the silver may be recovered later when the mercury residue is treated with aqua regia and then diluted. (The silver chloride separates out.) I n the authors' procedure these objections are overcome by extracting the lead chloride with an ammonium acetate solution containing acetic acid. Acetic acid is added to the ammonium acetate t o reduce to a minimum the hydrolysis of the latter. This must be done t o avoid loss of mercury, for the ammonia formed by hydrolysis interacts with the mercurous chloride and the resulting HgNHzCl enters into the lead chloride extract. The residue is then treated with aqua regia and after subsequent dilution with water and centrifuging, thelsilver is separated as chloride from the mercury.
Experimental
aid of a 1-ml. pipet add 1 ml. of concentrated hydrochloric acid. Stir for 2 minutes (to allow lead chloride to crystallize) and centrifuge for 3 minutes. The supernatant liquid now contains Groups I1 to V. Pour off and set aside. To the residue in the tube add 5 ml. of L reagent (a solution 2.6 M in ammonium acetate and 0.8 iM in acetic acid). Stir thoroughly for 0.5 minute and centrifuge until clear (not more than 3 minutes). Pour extract into another tube. Rrpeat with 5 ml. more of L reagent. Test for and estimate lead in the combined extracts by adding 2 ml. of potassium chromate. [A known number of milligrams of lead (say 20) are pipetted into a calibrated centrifuge tube (the blank or control) and the volume is made the same as in the unknown by using water and identical volumes (or weights) of reagents. When the potassium chromate is finally added simultaneously to both, the lead chromate which forms is allowed to settle under the influence of gravity (5 minutes). The number of milligrams of lead in the unknown is proportional to the volume of lead chromate in the blank. The procedure is similar for the silver (estimate as silver chloride) and the mercury (estimate as mercuric sulfide)]. Add 2 ml. of aqua regia to the residue in the centrifuge tube and boil down by inserting the tube in an upright position in a sand bath (to prevent bumping and subsequent loss of solution) until the aqua regia is destroyed (to about 1 ml.). Dilute the mixture to 10 ml. and centrifuge until the supernatant liquid is clear (an exceedingly faint cloudiness may be ignored). The residue is silver chloride. Pour off supernatant liquid equally into two tubes. To the first add stannous chloride reagent. A gray to black precipitate indicates the presence of mercury. Estimate it as mercuric sulfide (by passing in hydrogen sulfide) in the second tube only if a test has been received with the stannous chloride reagent. Add concentrated ammonia with stirring to the final residue (in the second paragraph preceding) until it dissolves. Add dilute nitric acid until the solution is just acid. Dilute to 10 ml. and estimate silver as chloride.
A new method proposed for the detection and semiquantitative estimation of Group I cations is much less timeconsuming than the classical one. It allows for the detecAND SEMIQUANTITATIVE ESTIMATION OF GROUP I CATIOKS tion Of about loo mg* Of TABLEI. RESULTSOF DETECTION metal as maximum with the (As performed by beginners in analysis a t Brooklyn College) lower limit of 0.2 mg. for silver Unknowna Ions Present Repprted b y Student Reported by Student Reported b y Studen? and mercury, and 15 mg. of A g + P b + + Hg+ Ag P b + + Hg A g + P b + + Hg A g + P b + + Hg Mg. Mg. M g . Mg. Mg. Mg. Mg. Mg. Ng. M g . Mu. Mg. lead, each metal alone or in 1 20 60 None 30 70 None 20 45 None 5 30 None the presence of each other. 2 5 95 None 25 40 None 3 5 70 None 10 45 None This method may be used in a 5 4 0 3 5 5 5 8 5 5 5 5 3 5 3 5 4 0 4 None 90 20 None 50 80 None 45 20 None 6 5 10 semimicro system of analysis. 40 10 25 75 10 25 25 50 25 15 5 30 30 6 None 30 40 None 15 40 None 45 50 None 20 80 Time of analysis is less than 40 None 10 50 None 30 30 None 55 7 50 None 10 30 minutes. 20 10 None 40 20 None None 50 20 None 40 30 8
In a 15-ml. centrifuge tube take the solution of the unknown (not more than 100 ma. of metal) and dilute to 10 ml. With the
a
20 None 9 20 10 10 None 40 None 10 20 11 100 20 5 12 13 25 None 25 14 None 20 None Three different students for each
15 None 25 20 None 20 None 25 20 220 10 5 50 None 50 None 50 None unknown: 42 etudents
10 None 26
10 20
None
20 40 None 15 None 15
None 10 80 75 70 None
60 None 25 30 10 None
30
30 None 25 None 25
None a
30
30 25
None
PRESENTEDbefore the Division oi Physical and Inorganic Chemistry at t h e 99th hleeting of t h e AXORICAN CHEMICAL SOCIETY, Cincinnati, Ohio.
