VOL. 3.
NO. 3
FINAL EXAMINATIONS I N GENERAL CAEMISTRY
313
FINAL EXAMINATIONS IN GENERAL CHEMISTRY* J. H. HILDBBRAND, UNIVERSITY
OF
CALIFORNIA. BERKELEY, CALIRORNIA
In meetings such as this we find a considerable degree of unanimity so long as we discuss generalities. We unite in asserting our belief in teaching the student to think and to have the scientific attitude of mind, rather than in cramming him with facts. But testimony in prayer-meeting does not always accord with conduct in everyday life, and Professor Cornog has called attention, as many of you will recall, to the fact that final examinations do not always bear witness to the emphasis asserted in our declarations of faith. But it is the daily life and not one's profession of faith which is truly enlightening, and I am, therefore, going to assume deliberately the risk of exposing to your criticism an actual view of the results of our teaching in the University of California, rather than to utter generalities which you might suspect to be insincere. Indeed, I believe that courses in chemistry have too long been judged upon a very unscientific basis. The impression a text-book makes on the teacher determines its use. The best seller is often supposed to be the best text. The good teacher is not distinguished from the popular lecturer. I am not an advocate of standardized tests, but I believe the most important criterion for judging a book or a teacher to be the kind of questions the pupils can answer. Of course, I do not wish to imply that the values of a course can all be tested by the final examination; the inspiration the student may have received, and the breadth of outlook, are among the most important results of good teaching although they can scarcely be tested by examination. The purposes and methods of the course we give in the University of California have been set forth in the introduction to the "Course in General Chemistry," by Bray and Latimer; also by myself in Science, 55, 355 (1922). Any repetition here is, therefore, uncalled for. In making the final examination questions for this course we have borne in mind the fact that great progress has been made in recent years in the technic of giving examinations which can be graded with a minimum of labor and without the uncertainties and inequalities in marking inevitable when the older type of examination is graded by a number of readers. The students like this type of examination both because the questions are exceedingly definite, and because many questions can be asked, so that accidental slips have but a minor effect upon the grade. Several samples of recent papers are presented herewith. The first is the final examination in the course in May, 1925. Following the custom adopted during the term this was an open book examination. We are coming to the conclusion that this plan more closely approximates the actual conditions of life, and that it removes * Presented before the Division of Chemical Education at Los Angeles. August, 1925.
emphasis from mere memory work. It will be noted that reference books would furnish but minor assistance in answering these questions. The average grade of the class in this examination was 67 per cent, and 18 per cent of the class secured grades of 80 and above. UNIYB~~SZIT 01) CALIPOBNIA
(Coune Examinations)
CHEMISTRY 1 8 , GENERAL CHEMISTRY, SECTIONS I AND I1 Instructor in Charge, Profersor HILDBBILANO Anmer all quertion this sheet in the manner indicated. Do not use "blue books." Ordinary reference books and the course note-books may be eanrdted as desired. NameofStudent Nameof LaboraforvInstruetor .............................................................. 1. Supply appropriate words in the spaces below. Do not guess, as a wrong word counts -2. h m the place of lanthanum in the Pcdodie System of elements its prioeipal oxide should have the formula. .................... m d its chloride the formula. ................ Its h". droride should b e . . ................................ soluble in water than Ba(OHl2and.. soluble in NaOH than aluminvm hydroxide. The free element should be n ................ conductor of electricity and should have e .......... ..melting point than barium. I t s ion should have .................. tendency t o form complex ions. (Credit 14) 2. Supply the equation and the mising word- io the following statement. Do not guess, for - 2 will be assigned for each wrong answer. An electric b n t t u y is made by using a cadmium amalgam for one electrode, another electrode of CI, a t 1 atmosphere svmvnding n graphite rod, and between them a Ml1ution of CdCI,. The equation for the reaction is. ....................... In this reaction the CII is the ......... agent. T h e electromotive force of the cell would be increased by ................... the concentration of CdCI,, by the cmcentration of Cd in the amalpam, by ............ the pressure of Cln, or by .................... the temperature, keeping the m re sure of Cl, at 1atmosphere. (Heat is evolved while the eel1 discharges.) (Credit 161 3. (a) How man= grams of iodine will be produced if 2 mots of NaI and 3 molo of &Clr nm mired in dilute acid solution? Ans. .................... ( b ) 500 cc. uf 0.2 M-Cu(NOr1, is wired wich 500 ec. of 0.2 M-Pb(NO,)1 and 27 g. of metallic a h minvm is added. After themaction is complete what ions will be present in the solution, and what
...........................................................................
..
..............
....................
.. 4.
(Credit 10) Write the formulas of the following subrtaneer in the spacer provided: (1) A constituent of @soline (2) An organic analogue of NaOH (3) An organic analogue of Na.0 .................................. (41 An organic acid containing 0 carbon atoms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . An anaesthetic .................................. (6) An abrasive .................................. (7) An insecticide .................................. (8) A P"et,. substance in dye manufacture .................................. (9) The poinono"seonstit"enfofilluminatinggas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Give the formulas of reagents that will (10) Dismlve CuS but not HgS ........................ (11) Dirmlve BaCrOd but not Bas01 ........................ (12) Dissolve SnSl b"t not s n s ........................ (13) Dissolve PhOI ( 1 4 ) Dissolve HgCI but not AgCl (15) Reduce H a t + hut not Ha+ i i ~ ) change S. to n2snol ........................ ........................ (17) Change BaCOa t o B S O , but not CsCOa fa CnSOa (18) Dirmlve PbSO. but not PhS ........................ (191 Dissolve A8 but not A" ........................ (20, Give a delicate t e r t i o r a fairly strong oxidizing agent . . . . . . . . . . . . . . . . . . . . . . . . (Credit 20)
(a
5.
6.
A solid unknoan was made by selecting certain of the following salts: =SO,, AsNO~,PbCh. FcSOd, (NHhSOs, CUSOI.Ba(NOdr, NazCrOa, C d S O J r , NanCOa. Upon treating the vnknoan with hot w t e r n white solid is left which, after filtration from the solution, is found to he soluble in 6 N-NaOH but in~lolublein 3 N-HNOa and insoluble io NHIOH. The filtrate gives a red color with litmus, yellow with methyl orange, and upon the addition of 6 N-NaOH gives a colorless solution with an odor of ammonia, and containing a suspended greeni8h precipitate. On the basis of these observations, underline all constituents in the a b m e list that are knoan t o be present, nw ont all that are known to be absent, and leave unmarked all whose v e x n e e is doubtful. (Credit 20) An unknoan solution is being tested f a the presence of the following ions or complex ions, etc.. t i derived hom them: Azi. - . Ali++. Ba . Cr+++. Cu++. Fet++. %++. He++.. Hz+. K + NH&+. Pb++, zn++,coa--, -0,--, CI-. Hi, OH-, N a - , so,-: All ions not listed may be m u m e d t o be absent. Distinct obsuvations are made upon separate portions of the original solution aa follow.: (a) The addition of N-COI solution causes effervescence a t &st, and added in excess gives a prceipitate. (6) Addition of B a c k solution gives no precipitate. (G) N-HISO, gives no preeipitate. (dl 6 N-NaOH in excess gives a colored precipitate, the filtrate from whieh is colorless and amelk of N&. (el H B gives a nearly white precipitate and the filtrate has a color different from that of the original solution. On the basis of there observations considered as a whole, underline the formvlas of ail constituents in the above list whieh are known t o be orerent inaooreeinhleconcentmtion. m s out all known .. t o he absent, and leave without mnlk all whore presence i. doubtful. (Crcdit 201 April-May, 1925.
. -
. . . .
The examination given to the same class at the end of the first term, Dec., 1924, was a closed book examination, here reproduced. The average grade was 63 per cent, and 12 per cent of the class received 80 and above. UNIVBRSIIY OP CALWOIINIA
(Course Examination)
CHEMISTRY 1A. GENERAL CHEMISTRY, SECTIONS I AND I1 Instructor in Charge, Professor Hn.mennno Answer all questions on this sheet in the manner indicated. Do not use "blue book$." Nameof Student ........................................................................... NameofLaboratoryInrtructor .............................................................. w r i t e the formulas of the followinp substance3 in the roacer orovided: Taoammoniacomplerionn ........................... (1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~
~
(2). ...........................
Adeliquereeotsalt.. ............................................................... Avolatilesalt..................................................................... The nitrate of a divalent element Bmic oxid A salt tha Cuprousaulfide .................................................................... A salt giving an a d d reaction when dissolved in water.. ................................ A salt giving an alkaline reaction when diaaoived in water.. ............................. Theehideonstitvcntofruby ......................................................... A metal which is nobler than zinc but baser than silver.. ............................... The two substances mixed t o make magnesia cement. .... (11. ........................... (2) ............................
.....
,rr.rlit 14,
An unknown solution is being tested for the presence of the foliowingiono, oreombinntionsof them: H f . OH-, Nat, K+.Cai+. Cui+, Znt+. Axr, NHd+, SO*--, CI; NOI-, COI--. All ions not listed m a y be a-umed t o be absent. It is found by experiment that the addition of
who* presence is doubtful.
(Credit 13)
3.
Another unknown solution may contain the following constituents but no others: Hi, OH-, K f , C=++,Na*, C u t + , Znt*, As*, NH
