CHEMICAL PROJECTS Research Ideas for Young Chemists JAY A. YOUNG, King's College, Wilkes-Barre, Penna. JOHN K. TAYLOR, National Bureau of Standards, Washington, D. C.
The Chemistry of Silver See SCAWENCK, J. R.,J . Chem. Edvc., 36, 45 (1959). Beginning with metallic silver, which is oridiaed to the ion in aqueous nitric acid solution, a. sequentid series of reactions is followed in which silver is precipitated. The steps fallow: first precipitate as the carbonate which is converted successively to the oxide and then to the chloride which is dissolved by the addition of ammonia, then reprecipitated as t,he bromide, dissolved w ~ t hthiosulfato, and precipitated once more as the iodide. Dissolution with cyanide follows and then precipitation as tho sulfide, which is reduced, by aluminum in hot aqueous carbonate media, to metallic silver once more. I n each case, the srscessive precipitates are progressively less soluble, and t,he complexes used to dissolve them have progressively smaller instabi1it.y constants. Questions: Show t h a t the order of addition of reagents, outlined in the
article is, or is not, important in order to obtain repetitive precipitations and dissolutions of the silver compounds and ionic species described. Select one or more parts of the series of steps described in the article and identify the reactions which occur. Can you extend thc series of reactions described, either h y additional steps between the precipitation of silver carhonate and of silver sulfide or h p extra, steps hefore or after these? Select mother metal instead of silver and devise a series of precipitations and dissolutions ahich depend, far their snccessful progressiw application in consecutive order, upon favorably decreasing mlubilitios of the precipitates and corrcspanding variations in the properties of the dissolving reagents.
The Preparation of Magnesium Nitride See FROMM, F.,
AND
RIVERA, P. .T., J . Chem. Edue., 21, 196 (1944).
Magnesium nitride can be prepared by passing nitrogen over heated magnesium: a procedure lor this preparation of magnesium nitride is described in the article. However, from the data cited, i t is clear t h a t most sitmples of powdered magnesium are contaminated with magnesium oxide. Magnesium oxide, alone, will not react with nitrogen under thc condit,ions described by the authors, although msgnesium oxide when mixed with metallic magnesium will react, according to the results ohtained by the authors.
lodomercurates
Questions: When magnesium oxide (mired with magnesium) reacts with ,,itrogen, farlning ,,itride, happens to the gen? Will m y other gmes, in addition to nitrogen, react with m a p nesium, with magnesium oxide or mixtures of these t.wa solids? What products are formed? Write equations for tho renetions which occur and verify their validity.
,
Sap I\~EYER, M., J . Chem. Educ., 20, 145-6 (1943).
Few componnds are as interesting as the iodomercurates. T h r y are brightly colored and change color when heated, or cooled. The preparation of many iadomereurxtos is straightforward; mixing of solutions of potassium iodomercurrtte(I1) and a salt of a. metal will yield the metallic iodomercurste as n precipitate in many caws. For example, in this reaction, 2Kt.IHeLI-- 2Kt Ae.[HeI,I 2Aef
+
+
Qvestionr: From the discussion in the article, using similar procedures or procedures which you devise, prepare other iodomercurates and determine their probable iormula, from the results of your snzlysis of the products. Some iodomercurates are heat sensitive, their compositian changes when the temperature is raised. Can you determine
A960 / Journal of Chemical Education
the nature of the compound, or mixture, formed nhen a heat sensitive iodomercurate is suhjeeted to a high temperature? Some iodomercurates are photo sensitive. What products are formed when such a. compound is exposed to light? Or, can this property be used advantageously in the preparation of photographic plates and films? Do you agme t h a t when a n attempt is made to prepare lead iodomercuratr(I1) by the method descrihed by the author, i t is contaminated with Ph(OH)?, either as a mixture or as a compound of fixed composition? Can you account for the fact t h a t the composition of basic bismuth iodomercurate varies from one preparation to another? C s n you prepare cadmium iodomercurate(II), succeeding where the author failed? What is the nature oi the precipitate formed when soluble antimony salts arc used, and 1vh.v does the composition of the precipitatevary, dependingupon the pH of the solution? (Continued on page A96Z)
