=en-Zvi and Judlth Sllberstein Science Teaching Department Weizmann Institute of Science Rehovot, Israel
I
1 I
The Use of Motivational Experiments in the Teaching of ~vantitative~once~ts in Chemistry
In recent years, the difficulties encountered in the teaching of the quantitative aspects of chemistry (e.g. the mole, molar mass, molar concentration, and molar volume) have drawn considerable attention (1-4). These difficulties should he considered from two angles-from the students' points of new and from the subject matter. For example, the worldwide democratization of education has brought a large and heteroeeneous . uonulation of students into the science classes. Some . of these are slow learners, many are non-scientifically oriented, and many, a t least in the early stages of high school, cannot cope with mathematical formulations and quantitative concepts. The quantitative concepts of the mole, molar mass, molar concentration, and molar volume form the basis of the language of chemistry. Research chemists and chemistry teachers agree that in order to present a meaningful picture of chemistw, these concepts should be introduced a t a verv early stage in the study of chemistry. The gap between the mental maturity of the students and the abstract demands of the discipline is a t least one of the main reasons for the feeling of students that chemistry is a borine. difficult. and non-auuealine suhiect. I t i s felt nowadays that ccekistry, like physics and biology, should be an integral part of the general education scheme given to all students. It is, therefore, impossible to confine the teachina of chemistw onlv to a selected erouu of students. On the other hand, i t does-not seem de&ahie to change the structure of the discidine comuletelv and to teach it in hieh schools without mak& use o f t h e q"antitative concepts. The authurs suggest that the way to bridge the gap between the student and the sul~jectmatter lies in the method of presentation used by the teacher. 'l'he presentations should be meaningful to the student. who should he cnco~~raged to hecome pcrsbnally involved in the learning process in order that his mutivation to cone with diiiicultie.i he enhanced. The present study is a n attempt to develop a teaching scheme in which these ideas are em~loved. In the followinKsection~,a~enampleofalearningsituntion will he presented, followed hy a disrussion of the natureof the changes introduced, and t h i n some results of a n evaluation of this scheme as c o m ~ a r e dto the curriculum used currentlv will be described.
" .
'
Teachlng of the Concepts of Mole and Molar Mass In many chemistry curricula (e.g. CHEMStudy (9, Chemistry for High School (6))the mole concept is introduced through the gas laws and Avoeadro's hvuothesis. In the uroposedtenching scheme, t he teaching of ;he mole is until after the students have familinrized themsr~veswith simple redox reactions and have learned to balance ionic equations. One of the equations studied is
would be needed to "manufacture" 100 g of silver using this reaction. At this stage, the students do not have sufficient background from which to draw the correct answer; as a result, the most abundant but incorrect answer was "50 g." When asked to give reasons for this answer, the student usually wrote ". . . because one copper atom is needed in order t o "convert" two silver atoms." This response came from the majority of the students, and although wrong from the chemical point of view, it id, of course, the expected answer taking into account the previous knowledre of ihe students. A minority of the students (about 25%) gave answers like: "It is impossible to tell since we do not know what is the weight of a given number of silver atoms or of copper atoms,." w e even got highly sophisticnted answers such as: "We have to know how many atoms there are in one gram ofsilver and what is the relationship between the mass of a silver atom and the mass of a copper atom. Since we need one atom of copper for the production of two atoms of silver, we can then calculate and multiply by the masses of the atoms." This minority of students, who did not give the wrong response have of course grasped both the need and the meaning of the mole and of molar masses. The majority of students, however, who gave the wrong answer were given the weights of copper and silver in a quantitative experiment and that faced them with the inaccuracy of their answer. The follow-up discussion between teacher and cl&s centered around the reasons for the discrepancy hetween the "expected (50 g~ and the actual (-30g) results. Studentsand teacher together reached theconclusion that it is not enough t o know the ratio between the number of atoms but the ratio of masses is also required. The Characteristics of the Teachlng Sequence 1)Enhancing the rnotiuotion of students to cope with difficult situations. Achievement motivation can he divided into an intrinsic factor (cognitive drive) and an extrinsic factor (egoenhancement and affiliation). Of these, thecognitive drive (the desire to know and understand, to master knowledge, to formulate and solve problems) is the important kind of motivation for meaningful learning (7). One of the methods suggested for the enhancement of cognitive drive is through the formation of a cognitive conflict. According to Berlyne (8) . . "if conflict is a drive. the reduction of conflict will he reinforcine and it will provide the explanntiun for the reward vnlur of invrstigating th~ngsthat are puzzling nnd the learning d knowlrdgr r e u l t i n g from this investigation." In the example of a teaching sequence described above, the motivation of the students was enhanced in two ways. First, hy the formation of a cognitive conflict. Here, the discrepancy between the expected and actual results created a conflict in the minds of the maioritv of students who had eiven thewrone answer. Theminoritv of bright ~. students.. of course., were not faced with such a conflict her a u s ~they knew the correct answer Fur these students, hoxrwr, the snr~sfnction01 reaching the correct answer acted nr reward in itself (8).Secondly by the use of novel and interesting situations. Novelty has a singular effectivenessin "engaging interest and for a time supporting persistent behavior" (9).In the above teaching scheme, the intrcduction of every concept is preceded by a presentation of a novel and puzzling or interesting situation such as the formation of a silver "Christmas tree." This is done in order to attract the students attention and to focus it on the problem discussed (see (10)). 2) Teaching toward meaningful learning. Ausubel and Robinson ~
~
With this information in front of them, the teacher demonstrates to hisher students the reaction. The silver "Christmas tree" which is formed by this reaction is quite spectacular, especially when viewed for the first time. This demonstration is followed by a written questionnaire, in which each student is required to balance the equation for the reaction and to determine how many grams of copper 792 1 Journal of Chemical Education
~~
~~~~
~
~~
~~
~
~
~~
(11) specify two dimensions of the learning process. One deals with the ways by which knowledge is made svailahle to the learner (reception learnin= and discover~learnind. The other deals with the ways in which the learner maiincorpo&te new information (meaningful and rote). In the suggested teaching sequence, an attempt was made to introduce each new concept only after a suitable background had been prepared and the need for the concepts was felt by the students themselves. (After the studentswere faced with the discrepancy between their answer and the correct answer, they understood the need to introduce the concept of the mole). In this way, meaningful reception learning took place in which the new, logically organized material could be related to already existing knowledge. 3) Students' personal ~nuolvementin the learning process. At various stages of the teaching sequence, each student had to respond to a written questionnaire. The questions did not ask for the recall of facts hut forced students to evaluate new and unfamiliar situations and to suggest theories that might explain the facts presented to them. In this way, every student was involved actively in the learning situation and had to concentrate on it. The teacher, in the follow-up discussion,could respond to his or her answers.
The same aspects, i.e. the cognitive conflict, the use of novel and interesting situations, meaningful learning, and the personal involvement of the students, were present to a greater or lesser degree in the teaching of the other quantitative concepts (molar volume and molar concentration). he various characteristics of the teaching sequence might be expected to influence low and high achievers in different wavs. ~ i g achievers h did not benefit from the cognitive conflict, s i m ~ l because v for them. in most cases this conflict did not arise.0n the other hand,'they had the satisfaction of the immediate reinforcement hv eivine the correct answer. have the correct responses reinThe low achievers did forced but benefitted from the formation and resolution of cognitive conflict. T h e aspect of personal involvement was verv important since these students usually do not participate very actively in the lessons. T h e introduction of novel situations, and the attempted meaningful learning are important for both low and high achievers. It was hypothesized, therefore, that such new teaching sequences will make the learning of some of the quantitative aspects of chemistry easier and more appealing than current methods for hoth the good students and the slow learners. A Comparative Study of Teaching Strategies Twenty-three 10th grade classes took part in this study. These were divided into an experimental group (N = 435) and a control group (N = 273). Prior to the teaching period a pretest was administered and hoth groups were found to be eauivalent. The expermental group was taught according to the lines descrihed above while the control a o u followed ~ the currentlv used curriculum "Chemistry f i r ~ i School" ~ h (6). ~ h k teaching sequence in the control classes was an introductory chapter summarizing some basic concepts in chemistry. This introduction was followed hv mass-volume relationships (stoirhiometry intnduced thriugh the gas laws) and then b y oxidation-reductioa. Fur the trial classes, both teaching methods and the order of introdurtion of the concepts were diftrrenr, a9 d~scrihedabove (i.e., the teaching of the mole concepts was postponed till the students had a working knowledge of oxidation-reduction reactions). Hoth groups were given a written pretest at the beginning of the school year, examining their knowledge in general b i o l w . and hasic rhemistrv. The u Cronbach science. nhvsics. " reliability coefCicientiZ2) for this test was calculated to be 0.72. About the middle of the year, a three-part written achievement test was given to hoth groups containing (a) questions relatine to the quantitative (mole) aspects of on redox reactions, and (c) &estions ;hemistry, (b) relating to other areas of the subject taught in the 10th grade
~,.
(i.e., the structure of the atom etc.). The a Cronbach reliability coefficient was 0.71. At the same time, a questionnaire was given to a random sample of about half of the students from each of the two groups. This questionnaire ronsiited of' two parts. I. A list of I 4 concepts. covering those studied during thesemester. The studenr~had t u resound on a four-point Liken type scale on the degree of difficulty and interest of each of these cbncepts. The a Cronbach reliability coefficientswere 0.89 for the difficulty scale and 0.87 of the interest test. For the subsequent analysis,the concepts were grouped into three categories-concepts relating to redox reactions, those relating to the mole, and general concepts. 11. A list of five items was given: (1)The language of chemistry, (2) Electrolysis and transfer of electrons, (3) Redox reactions, (4) The mole and molar masses, and (5)Molar volume and concentration. The students were asked to rank these items: (a) in the order of difficulty and (h) in the order interest. Results and Discussion
An analysis of the results of the achievement test showed no simificant difference between the two groups in total score nor in the scores f ( ~the r questions relatingto the mole concept and those re la tin^ to the general concepts. The experimental group was somewhat better than the trial group in the subtest of oxidation-reduction. T h e comparison of the mean ratings of each of the groups as to the difficulty and interest of the various subjects is given in Table 1.It can be seen that the experimental group found that all the conceDts were less difficult than did the control group in spite of: the fact that there was almost no significant difference in achievement between the two groups. These differences can be attributed to the fact that changes Table 1. A Comparison between the Opinions of Experlmentai and Control Groups
Experimental Ranae Difficulty Redox reactions
Mole concept General concepts
(N = 270) M S.D.
Conbol
(N= 115) M
S.D.
t-value
5-20. 4-16 5-20
14.33 11.75 15.46
2.84 2.65 2.55
13.35 10.52 14.58
2.93 2.65 2.30
3.01 4.26C 3.43O
5-20b 4-16 5-20
14.45 11.37 14.03
3.00 2.72 2.38
14.51 10.06 13.86
2.66 2.44 2.52
0.20 4.53' 0.61
btemst
Redoxreactions MoleconceDl General concepts
me lowest number = very m n i ~ i t me himst number = very easy 'me iowsst number = u w bwing me highest number < 0.001
*p
-
very intereating
Table 2. A Comparison between the Opinions of High Achievers and Low Achievers (Experimental Group) High
achievers Range
N = 165 S.D.
M
Low achievers N = 105 M S.D.
t-value
Difficulty
Redox reactions Moleconcept General concepts
5-20' 4-16 5-20
14.85 12.30 15.96
2.79 2.49 2.38
13.39 10.89 14.64
2.75 2.68 2.61
4.245 4.36O 4.21r
5-20b 4-16 5-20
14.75 11.52 14.00
2.58 2.79 2.58
13.88 11.12 14.07
2.58 2.61 2.06
2.41 1.20 0.24
interest
Redox reactions
Moleconcept General concepts
.me lowest number = very dlftlcull
The higheat number = very easy me lowest number = very boring The highest number = very Interesting
'p < 0.001 p 0.05
