The Mole: QuestioningFormat Can Make a Difference John N. Lazonby Department of Education, University of York, York YO1 5DD, UK Jane E. Morris The Mount School, York YO2 4DD, UK David J. Waddington Department of Chemistry, University of York, YO1 5DD, UK The mole is an international unit. To judge from a plethora of papers, i t is also recognized as a scourge for school and college chemistry students internationally (I)for there are examples of papers from France ( 2 ) , Federal Republic of Germany (3-51, Italy (6). and the United Kingdom (7-9)in recent years, all concerned with the difficulties students have in learning about the mole. In eeneial. the concent is assessed in examination bv calcul&ns which demani of students several steps. In a study with 2.695 students aeed 15 and 16. we found that it is not the individual steps but i e sequentii piecing together of these items that ~rovidedthe orime difficultv. In other words. it may be t h e way studenis are tested that leads teachersto believe that the level of understanding is low (9.10).Several people, including Howe (8)and MO& ( l l ) , have previously found that students who could cope with individual steps in a problem had difficulties in handling several steps in a more complex calculation. The results of our studies suggest the order in which the individual steps are mastered does play a critical role in understanding the topic (9). ~
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The Study
Sixteen-year-old students, in the top 20-30% ability range in England, Wales, and Northern Ireland, take a public examination known as Ordinary Level. Many students take this examination in 7-10 subjects, one of which may he chemistry. Following a study of examination papers taken over the last four years in chemistry, we selected three questions that were typical of those concerned with molarities of solutions. The questions tested the following operations: calculations of relative molecular mass, conversion of mass into number of moles and vice versa, making deductions from a given equation (involving ratio and proportion), and calculation and use of molarities of solutions. The 652 students involved in the study were given one of three tests, all hased on three examination questions. Test A consisted of three sheets of paper, each with one of the three questions given at the top of a page and with space for working and giving the answer on the same page. The following is an example of one of the questions. Silver chloride (AgCI) is formed in the following reaction: AgN03 + HCI
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AgCl + HN08
Calculate the maximum yield of solid silver chloride which can be obtained from reacting 25 em3of 2.0 M hydrochloric acid with excess silver nitrate. (AgC1 = 143.5) In Test B, each of the same three questions was presented on seoarate sheets of naner. . . . but this time in a structured sequence of four parts, leading the students through the question. For example, the question above was restated thus: 60
Journal of Chemical Education
Silver chloride (AgCL) is formed in the following reaction: AgNOa + HCI
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AgCl + HN03
How many moles of silver chloride can be made from 1 mole of hydrochloric acid? (b) How many males are there in 25 em3 of 2.0 M hydrochloric a"d? ( c ) How many males of silver chloride could be made frnm the number of moles of acid in (b)? (d) What is the mass of the number of moles of silver chloride in (c)? (AgCI = 143.5) Test C contained the same 12 short questions from Test B, hut each was written as a stand-alone question. They were distributed through the test in a random order so that the answer to any one question could not he obtained from a previous question. For example: (1) How many moles are there in 25 em3 of 2.0 M hydrochloric acid? (2) What volumes of 1.0 M hydrocloric acid is needed to provide 0.2 moles of the acid? (3) 0.01 moles of a solution of sadium carbonate were mixed with 0.002 moles of hydrochloric acid, and the following reactions occurred: (a)
+
NasC08 + 2HC1- 2NaCI Hz0 + COz Is the hydrochloric acid or the sodium carbonate in excess of this reaction? Tests A and B were used to investigate the effect of structwine.. ouestions. Test C was desiened to see whether each s t e ~ . or operation was intrinsically difficult or whether it was only difficult when part o f a series uisteps (81 operations. The Findinas -
The students' scores iur Tests Band (: were much higher than those for'l'est A. showina the structurinp:of the auestiun makes it easier for students to show their understanding of the subject. Analysis of the individual questions involved shows a i i m i ~ aoutcome. r The results on the^ and C tests were very close, with Test C having a slight edge in two of the three questions. I t may seem to students that Test C, with its distinct, one-s$ep questions, is simpler to answer than the structured questions in Test B where one has to carry even a small amount of information from one part to another. In Test A. this is magnified even further so the fall-off in success on " going from step (a) to step (d) increases in the order Test C, Test B, Test A. This is shown vividly in all three questions. A strategy that is suggested by this work is to teach and practice individual steps involved. As far as is practicable, the teaching order should he determined from the relative difficulty of the operations as perceived by the students. When students are confident of these operations, they can he introduced to questions needing two, then three and four steps.
Teachen have tried successfully,using the three types of tests (C, B, and A in that order) during their teaching to give students more confidence. Our have not on teachingmethods but on the way we assess students. We as teachers and examiners must carefully decide whether we are attempting to test stedents' command of the principles or their ability to solve problems. The authors were impressed by the considerable interest expressed by the teachers throughout their project, much of it springing from their own concern about the difficulties experienced by their own students in understanding the topic.
Literture Cited (11 uierka. w., stud. s c i E ~ U C8,93 . , (1981): EULJ s c i E ~ U C3, . , 145 (19811. (21 Chastretle, M.. and C m , n.. proceedings 01 the sixth lntemationd conference on Chemical Education. (Editor: Lippincoft, W.T.1, University of Macylend, iJ8I. (3) Diorks. W.. "Co-operation between Science Teachers and Mathemstica Teachers,'' proceodingsof the ~ i ~ k f conference, dd 1978, lnrtitut fur ~ i d ~ k tdei ik~ e t h ~ ~ ~ t i k des Universitat Bielefeid. ,979. (41 W,,and ,J,,J. CHEM,EDUC.,inpress, (51 Schmidt, H.J., School sci. R ~ u .66,156 , (19841. (61 Ceruellati, R.. Montuschi. A,, Perugini.D., Grimellini-Tomssini, and Peeori Bdandi, B.,J. CHEM.EDUC.,59,852 (19821. (7) For example, lngle, R.B., and Shayer. M.,Educ. Chem., 8,182 (1971): Dunern, I. M.. and ~ o h ~ ~A. tH.,o E ~ U~C .them.. , 10,213 (1973): H U ~ ~ O DM. J., E ~ U Ccham, 13. 91 (197fil; Gower, D. M., Daniela, D. J., and Lloyd, G.,School Sci. Rau., 58, 658 (19771. (8) nowe,T. v.. M.SG thesis, ~ ~ i v c r a i tG~ Ia ~f ~ ~1975. OW, (91 Lazooby,CN., Morris, J. E., and Waddington, D. J., Educ. Chem, 19,109 (19821. (101 Cassels,J.R.T.,and Johnstone,A.H., J. C~~~.E~~~.,61.613(1984). (11) Morris, J., MSc. thesis, Univ~rsityofEest Angiis, 1977.
Volume 62 Number 1
January 1985
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