David Hayes Three Rivers Communitv Colleae Poplor B .a, M~ssour 63901
II
A Laboratory Practical for a First-Semester Chemistry Course
In current educational trends, the use of hehavioral objectives is becoming increasingly important. Experimental laboratory work performed by the beginning freshman in a first semester chemistry course can be evaluated in terms of behavioral objectives. A laboratory practical can then he useful in evaluating the student's progress in attaining these objectives. The ideas of a laboratory practical' and an educational approach from the behavioral objective viewpointzhave currently appeared in THIS JOURNAL.
designated time limit, a practical examination is given which assesses the students performance in terms of the assigned hehavioral objectives. Table 1 Table 2. Question Samples for Laboratory Examination I Site Number
Outline of the Laboratory Course
Question or Instruction
iug information? Average mass = 13.92 g; Averase volume = 7.73 ml Metal Density (g/ml) Al 2.70 Ba 3.51 Pb
The laboratory part of the course is divided into four units, each unit consisting of three experimental laboratory problems. Each unit becomes increasingly more difficult. After the completion of a unit within a Table 1. Sample of Behavioral Objectives Laboratory Unit I Objectives: As a result of the laboratory experiments in Unit I, the student should be able to: 1. Define the followine terms: matter. substance. mixture. phya~mlproperty, ehernical pmprrry, demiry 2. 1.1s~ thc bnsir. Inborntmy safrty rules 3. Explain what iis meant by the law of conservation of mass 4. Examine a mixture and determine whether it is homogeneous or heterogeneous 5. Determine whether one substance is soluble in another 6. Use a handbook to reference physic4 data. 7. Use a balance to weieh an obiect 8. Deterrninp the density of a metal experimmtally 9. Plot a mas-volume relxtmnship from euperirnmtklly detcrmined poinu 2nd determine the slope of the bcst strn~ghtlme through those points 10. Calculate an average from a set of numbers 11. Arrange a group of metal8 in their order of decreasing reactivitv from eiven exnerimental data or from exneriacid
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(1) Weight the metal provided to the nearest 0.1 g (2) Record the volume that this metal displaces in water Compute the density of rhe metal sr Site 5 \\'rrtea ehcmtcnl cqmtion for the re~ction
Mg 12
13 14 16 18
+ HCI-
(1) Take a small amount of each of the provided metals, A, B, and C, and place these in 3 small test
tubes (2) Add 1 ml of dilute HC1 to each test tube and record your initial observations (3) Take the 3 test tubes to Site 13 of the chemicals and test tubes as described Arrange the 3 metals from Site 12 in their order of decreasing reactivity Test the solubility of s. small amount of the solid in water Examine flasks A, B, and C. Determine whether the components of these flasks are homogeneous or heteroeeneous
pose
gives a sampling of some behavioral objectives for a typical beginning unit. Outline of the Practical Exam
A series of examination stations is constructed in the laboratory. Instructions are provided at each examination site. The students proceed through the examination with an allowable time limit of 4 min at each site. Table 2 gives a sampling of the type of questions asked at various sites. Results
The laboratory practical given over Unit 1 gave a good indication of which behavioral objectives were attained by the students. For example, 94y0 could define matter, 97% could arrange three metals in their order of decreasing reactivity, 97y0 could use a handbook to find the melting point of sodium chloride, and 94% could correctly take an average volume from four data points. On the other hand, those behavioral objectives which were not attained by the students were also in evidence. For example, 22% could not correctly determine whether a given substance was soluble in water, 25% could not accurately determine
the density of a metal, 31% could not write an equation for the reaction of magnesium metal with dilute hydrochloric acid, and 67y0 incorrectly identified a homogeneous substance as being heterogeneous. Conclusion
The results of the laboratory practical certainly evaluated a students progress in attaining a particular set of behavioral objectives. The difficulties encountered can be immediately corrected before the pursuit of the next laboratory unit is allowed. The author feels that this gives a student an opportunity to demonstrate his ability for experimental competence. Acknowledgment
The author is indebted to Mr. James E. Rawlings, Mr. Gerald Malmstrom, and Mr. James Moroni for their invaluable suggestions for improvement of the manuscript. IHARRIS,W. E.,
AND
KRATTOCHVI~ B., J. CHEM.EDUC.,
48,543 (1971). a ~ I K I N J., , J. CHEM. EDUC.,48,615
(1971).
Volume 49, Number 10, October 1972
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