Detecting Nitrite and Sulfamate Ions in Qualitative Analysis See BRASTED, R. C., J. Chem. Educ., 28,592-3 (1951). Sulfamic acid reacts with nitrite ion to farm hydrogen sulfste ion, nitrogen, and water. Hence, the evolution of a gas when either reagent is added t o a solution suspected to contain the other probably indicates the presence of the suspected substance. Other possible gaseous products (from other components), such as hvdroeen . .. sulfide. carbon dioxide.. etc...can he identified readilv:. , i u :dIiticm, tltr lylrogrn wlfaw ion, whioh i6 d w f < m ~ .when ~d a u l f ~ m ~ or r c nitrite is prrsmi and thv mrrraymrdirrr ; ~ l t r r r n r r rr:t:cnt d d r d , can br idvntifiwi by n sword cu,>firrn.truryr t w Possible interferences due to other ions and methods for eliminat,ian of such effects are discussed. Quartionr:
Can the interfering effects of m y of the ions mentioned by
Brasted be eliminated by procedures other than those described in the article? Can you find any ions, in addition to those mentioned, which will interfere with this test for nitrite or sulfamate ion; can you devise a suitable procedure to eliminate this interference? There are many pairs of substances, such as silver ion and chloride ion; either can be used to test for the presence of the other ion. As in the ease described here for sulfamate and nitrite ion, however, interferences from other substances often complicate or preclude the use of these simple tests for the presence of either member of the pair. Select any suitable pair of substances and devise procedures to eliminate the effects of any other substances which would otherwise interfere.
The Use of Starch-Iodate Paper in Qualitative Analysis See LUNDIN,J. A., J. C h a . Edue., 28, 122 (1951). Starch-iodste paper turns blue when expnsed to sulfur dioxide.
It is propared by moistening a piece of filter paper with s. drop of each of the following solutions: starch, potassium iodate, and dilute nitric acid. This test paper can be used t o distinguish between esrbanste and sulfite; other distinguishing tests are less simple. Questions:
Arc there any other gases, in addition t o sulfur dioxide, which will cauae the paper t o turn blue? If so, how can these interferences be effectively eliminated when this test paper is used in qualitative analysis? Lundin states that as little as 0.3 mg of sulfite ion can be detected by this method. Does the concentration of the 0.3 mg of sulfitr ion make any difference?
What is the sensitivity of this test paper and is this value altered by varying the concentration of the solutions, or the amounts, used in the preparation of the test paper? Account far any sueh effects, if found. Lundin states that starch-iodate test paper can also be used to identify several ions, directly, in solution. Can you prepare still other test papers which will distinguish between these several ions, once the starch-iodate test paper indicates that one or mare of them is present in solution? I t should be possible t o use a series of specially prepared test papers, in combination with a few chemical separations, to completely identify the components of a solution containing several cations and anions; devise such a series of test papers and work out a qualitative analytical scheme involving their use. (If you wish t o perform s. complete study, determine the sensitivity of y o w t e d s for each cnt,ian nnd anion.)
Vanor Diffusion Methods in Qualitative and Quantitative Analysis See KITGHES,H., J. C h m . Educ., 28,195-197 (1951). A small, shallow glass dish, not unlike a Petri dish, is used in this procedure. The mid-region of the interior of the dish oansistn of a central compartment bounded by a rim, lower than the outermost circumferential edge, and concentric with it. An indicating reagent is placed in this central compartment, and a reagent which will react with the substance t o be analyeed and yield a volatile product is placed in the surrounding annular space. The substance t o be analymd is introduced into the annular compartment and the apparatus is covered with a flat glass plate. The time required for a. change in color, the a p pesrance of a precipitate, or other observable phenomenon in the central compartment can be used to cdculate the quantity or concentration of unknown in the annular compartment. Prior measurements with a known solution are necessary. Several variables must be controlled for.precise results. These include temperature, method of adding the unknown, the manner of mixing the liquids in t h e annular oompartment, the thickness of this liquid layer, and the intensity of radiant light falling upon the apparatus. The glass apparatus, called a "Conway unit," is not rendily available; but a suhatitute suitable for most pro-
Questions:
Repeat the pracedurc described and determine the percentage of nitrogen in an impure ammonium salt. Modify the procedure as necessary in order t o determine the percentage of hypoohlorite, chloride, sulfite, carbonate, or cyanide, in an appropriate sample. Many inexpensive automotive antifreeze liquids contain methyl alcohol. Determine the eompasition of sueh an antifrewe. Some disinfectants contain formaldehyde or phenol. Determine the composition of s. disinfectant and compare your analysis with that indicated an thelabel. Carry out the procedure described for the determination of nitrogen, or carry out a similar procedure for the determination of hypochlorite, ohloride, or sulfite, and determine the limits of precision of your procedure. Can the recision of this method be im~rovedso t h a t it is comparable to the preci~ionobtainshle from the more common methods of analysis?
ERRATUM:Dr. Gerald J. Cox, University of Pittsburgh School of Dentistry, points out the spelling error on page A263 of the April Chemical Projert,s. He passes on thp advice he gives his students, "Do not knock the 'I' out of Hnssrlbxlch."
A422
/ Journal of Chemical Educafian
