The Preparation of Pale Greenish-White Ferrous Hydroxide

Harold J. Abrahams and Stephen M. Poppel1Public High Schools of Philadelphia^ Pennsylvania

The color of ferrous hydroxide, obtained by precipitation resultingfrom mixing solutions of ferrous ions and hydroxide ions is variouslydescribable as ranging from blue-black or green-black to light green.One prescribed method2 for the preparation of a lightly-colored

product is based upon numerous studies3 and is rather involved andtroublesome.The method which we give below is easily carried out and makes it

at once easily possible for a person who has never seen the unoxidizedproduct to observe its true color without going to great lengths toobtain it.PREPARATION OF PALE GREENISH-WHITE FERROUS HYDROXIDE

1. Bring 50 cc. of distilled water to the boiling point and continueto boil for one minute.

2. Into each of two six-inch test tubes, place between 5 and 10 cc.of the freshly-boiled, cooled distilled water, prepared in step 1.

3. Into one of these test-tubes place one gram of pure ferrous chlo-ride crystals, and either two small iron nails or a strip of cleaniron. Immediately add enough mineral oil to make a layer about

^ inch thick. Now agitate gently in order to dissolve the crys-tals, without churning air into the water.

4. Into the other test-tube place 1 gram of pure sodium hydroxide.(CAUTION: do not use ammonium hydroxide.) Immediatelyadd enough mineral oil to make a layer about i inch thick. Nowagitate gently as in step 3.

5. Immerse both test-tubes in a mixture of ice and ammoniumchloride contained in a beaker or basin.

6. When the temperature has fallen to about 2°C., pour the sodiumhydroxide solution into the ferrous hydroxide solution.

The product thus produced is of a pale greenish-white color whichdoes not darken perceptibly on standing unstoppered (except for thesealing effect of the mineral oil) for a period of at least 10 months.

If the preparation of ferrous hydroxide is allowed to take place bymerely mixing solutions containing ferrous and hydroxide ions, with-out exclusion of air, the product is so very nearly black, that carry-ing out two precipitations, one by the new method proposed herein,

1 Second year student.2 Ludwig Vanino, "Praparativen Chemie," (Stuttgart, 1925), Volume 1, pp. 628-629.3 a. Compt. rend., 84:443 (1887); b. Ann., 95: 116 (1855); 63: 101 (1840); c. J. Prakt. Chew., 76: 239 (1859),

d. S. A. Ber., 44: 1608 (1911).

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and one by merely mixing solutions of both ions offers a striking con-trast and an opportunity to study the relative value of the methods.The method also offers an excellent example of a) the air as an oxi-

dant and one simple way in which its action may be prevented andb) the easy transition from the lower to the higher valence states ofiron.

OTHER REFERENCES ON FERROUS HYDROXIDEHARRY B. WEISER "The Hydrous Oxides." (New York, 1926), pp. 74-75; J.

Phys. Chem. 19: 232 (1916); Liebig’s Ann. Chem. 22: 56 (1838); 36: 101 (1840);Compt. rend. 69: 179 (1869); 109: 266 (1889); J. Chem. Soc. Japan 43: 397(1922); J. Am. Chem. Soc. 47: 70 (1925); J. Chem. Soc. 119: 932 (1921); Ber.71: 992 (1938); Z. anorg. Chem. 174: 145 (1928) and 251: 414 (1943); Natwms,31:326 (1943).

THE UNCERTAINTY ATTITUDE: A TEACHING OBJECTIVERobert C. McLean, Jr.

Physicists, having established the "uncertainty principle/5 can be credited, orblamed, as the source of this suggestion for a new phrase in pedaguese: "The un-certainty attitude." This is not a new concept. The set of words, however, is pre-sented as a general name for several objectives of science and mathematics edu-cation which have hitherto not been recognized as constituting a group.The simplest example of the use of the uncertainty attitude arises in the

solving of arithmetic exercises: "Check your work!" This admonition, in termsof the suggested principle, would be considered an expression of the necessity toindoctrinate the student with an attitude of uncertainty about the correctnessof his calculations.A second example of an attitude encompassed by this phrase is the admoni-

tion: "Accept nothing as true without proof!" Some teachers enthrone thisattitude under the title "scientific attitude." The most common use of it actuallyis in the geometry class, where it is generally not dignified with any title whatso-ever. The corollary of the scientific attitude, that one must accept some thingsas true without proof, also falls under the classification of the uncertainty atti-tude. The prime example of this is the development of non-Euclidean geometries.Thus, even that which one treats as "true," may give way to further "truthes."A third example, which follows from the second, is the fact that scientific

knowledge outraces the textbooks. Whereas the axioms and postulates ofEuclidean geometry are presented as a list of assumptions, the laws of the varioussciences are often taught in class as if they were whole and complete and thatfuture discoveries will leave them unchanged. This approach is contrary to thatof the uncertainty attitude. The teacher who is sincerely trying to achieve ap-preciation of scientific development must prepare his students for the future dis-coveries of scientific research which may revolutionize the principles and lawswhich the student is so confidently studyingAlthough politicians and generals may not wish the people under their govern-

ment to take an attitude of uncertainty toward their superiors or even towardeach other. (A soldier must have self-confidence!) In the science and mathematicsclassroom, it would seem to be a denial of the lessons of the history of scientificachievement to foster any attitude other than that of uncertainty�uncertaintytoward the pronouncements of the teacher and the textbook, uncertainty towardthe present knowledge of science, even uncertainty toward one’s own abilities.Such uncertainty should be expected to lead toward more careful work, moreintensive study, and a dissatisfaction with incompleteness.