Submicrorepresentations of chemical concepts
Saša A. Glažar, Iztok Devetak
Faculty of Education, University of Ljubljana, Slovenia
[email protected]
How do Slovenian students understand the submicrorepresentations of some chemical concepts?
Concentration of solutions, acid / base strength
SAMPLE
!
200 secondary school students (average age of 18), who chose chemistry as a Matura exam,
!
214 first year university students (average age of 20) - university program: Primary School Teacher; Biology and Home Economics, Physics and Tehnical
Studies, or Mathematics and Tehnical Studies.
METHODOLOGY
Two tasks from the paper-and-pencil test were analysed:
TASK 1
TASK 2
The aqueous solution of the same substance is in the beakers A and B. Solution A has twice the volume of
solution B. Complete the pictures with the solvent particles to show that:
The following pictures represent solutions of three salts NaA (A- = X-, Y-, or Z-); water molecules have
been omitted for clarity:
a) solution A is more concentrated than solution B.
- the solvent particles
A
B
b) the two solutions have the same concentration.
- the solvent particles
A
NaX
B
NaY
= A-
Legend:
NaZ
= Na+
= OH-
= HA
A- = X-, Y- , Z-
C) solution A is 1/3 the concentration of solution B.
a) Arrange the anions X, Y and Z in order of increasing base strength. __________
b) Why does each box contain the same number of HA molecules and OH anions?
_______________________________________________________________
- the solvent particles
A
B
McMurry, J., Fay, R.C. (1998). Chemistry. Prentice hall, Upper Saddle Ruiver, New Jersey, 628.
Heyworth, R. M., (1999). Procedural and conceptual knowledge of expert and novice students for the solving
of a basic problem in chemistry. International Journal of Science Education, 21 (2), 1995-211.
! the proportions of correct answers were calculated
! the common misconceptions of selected concepts were identified
! Some ideas for applications in the teaching process to eliminate detected misconceptions were established
RESULTS
80
77.6
80
70
68.7
70
56.1
60
60
51.8 52.8
50
46.2
41.6
56.7
50.5
49.5
41.1
27.7
22.4
30
47.9
46.8
50
35.7
% 40
% 40
30
29
20
20
20
9.5
10
0
2.3
2
2.3
0
10
6.1
7.6
5.3
0
0
0
a
correct SS
b
correct US
incorrect SS
correct SS
c
incorrect US
SS - secondary school students
no answ. SS
correct US
incorrect SS
Part a)
no answ. US
US - university students
incorrect US
no answ. SS
no answ. US
Part b)
SS - secondary school students
US - university students
Chart 2. The success of university and secondary school students in
solving the second task
Chart 1. The success of university and secondary school students in
solving separate parts of the first task
!
70.5
72.3
Students do not have developed proportional reasoning
Part a):
The most common wrong answers are:
A
!
B
A
B
A
!
the wrong sequence of anions regarding their base strength X-, Z-, Y- (25.3 % of secondary school
students; 15.2 % of university students); students from both groups concluded that the fewer OH- anions
there are in the aqueous solution, the stronger base is the base of the A- anions,
!
students did not write down ions but charge less particles (Y, Z and X - 5.7 % of secondary school
students; 8.8 % of university students) or the whole formulae of sodium salts (NaY, NaZ and
NaX - 5.7 % of secondary school students; 5.3 % of university students).
B
Students do not understand the particulate nature of the solution
- They either drew the solution as a solid state of the matter (15.0 % of secondary school students;
18.2 % of university students)
Part b):
A
B
A
B
A
B
- or they drew a solution in which the arrangement of the particles represents the solvent as a
participate (20.0 % of secondary school students; 22.4 % of university students)
A
B
A
B
A
The most common wrong answers are:
!
!
!
the solutions are in equilibrium,
salts are formed in the process of neutralisation,
sodium salts are neutral.
B
- Both mistakes (3.0 % of secondary school students; 4.7 % of university students)
A
B
A
B
A
B
CONCLUSION
!
secondary school students are more successful in solving this task than university students (tested secondary school students choose chemistry to be
their Matura exam at the end of the secondary school, so these students are better in chemistry than university students) university students do not
study chemistry, but chemistry is just one of the subjects in their program, which they have to pass to become primary school teachers
!
not even 10 % of the students from both groups were able to move easily from concepts represented in drawings to verbal descriptions of this
submicrorepresentation
APLICATION FOR SCHOOL
Teachers ought to:
!
use submicrorepresentations in science learning and teaching lessons in the elementary school (example: state of matter…)
!
use submicrorepresentations as a tool for objective evaluation of students' understanding of chemical concepts at all levels of chemical education, but
the complexity of problems must be adapted to the schooling level
!
devise submicrorepresentational conceptual tasks which can show possible misconceptions regarding the particle level of chemistry, so that teachers
could intervene in the students' reasoning process before conceptual knowledge completely forms, thus making the eventual conceptual change easier
!
develop science curricula materials in a way that promotes connections between students' macroscopic and their scientific submicroscopic
explanations