Chemistry Reference
In-Depth Information
- Which substances conduct when in aqueous solution?
NaCl
Na
2
CO
3
CuSO
4
KNO
3
KOH
All correct
57%
16%
12%
9%
7%
0%
- Which substances are built of ions?
NaCl
CuSO
4
CaCO
3
MgO
KOH
All correct
50%
36%
28%
22%
17%
3%
On average, the general chemistry knowledge of the students leaves a lot to be
desired. This holds true for both girls and boys. Overall, the pretest results of the
boys were significantly better than those of the girls (
p
<
0.001 according to the
U-test of Mann-Whitney).
9.11.4 Posttest Results of the Students
Towards the end of the teaching unit the students were given an unannounced
posttest, which they had to fill out anonymously. The aim was to test acquired skills
and content knowledge that was spontaneously accessible without prior repetition
or grade pressure. Transfer of knowledge was required to solve these problems.
Two examples might illustrate what students were able to accomplish and what not.
Problem 1.
Six molecular formulae of substances were given in problem 1. The
students were not explicitly familiar with these formulae. These formulae
represented bifunctional molecules with different orientation of the functional
groups. The molecules could be assigned to the following substances: succinic
acid, 2-hydroxypropanoic ethyl ester, ethylene glycol, malonic acid monomethyl
ester, 2-hydroxypropionic acid, and methyl propanoate. The students were asked to
identify all functional groups and to predict the behavior of the corresponding
substances in the test reactions. The following results were obtained:
- Eighty percent of students recognized all alcoholic groups, 61% all carboxylic
groups, and 40% all ester groups. Altogether, 47% of the students recognized at
least 8 of the overall 11 functional groups correctly.
- Seventy-six percent of the students predicted the reaction of the substances in the
cerium nitrate test (group test for alcohols) correctly, 74% the reaction in the
BTB test (group test for carboxylic acids), and 59% the reaction in the Rojahn
test (group test for esters).
- The majority of the students could predict the results of all tests correctly,
although a considerable percentage of them had trouble to identify the ester
group in the molecule.
