A longitudinal study of 16 - 18 year old students' understanding of basic chemical ideas.

The understanding 16 - 18 year old chemistry students have of basic chemical ideas
was probed in a longitudinal study using a test paper comprising twenty-three
diagnostic questions. The students were attending schools and colleges in the UK and
had chosen to study chemistry beyond the age of 16. They responded to questions
investigating their ideas about the differences between elements, compounds and
mixtures, the conservation of mass in chemical reactions, chemical changes and
chemical bonding. Aspects of stoichiometry, thermodynamics, equilibria and rates of
reaction were also featured. Students' responses were collected three times: at the
beginning, in the middle and towards the end of their Advanced ('A') level courses. The
written data was supported by interviews with selected students carried out after the
first and second surveys.
The first survey (of 399 students) established a baseline against which students'
progress could be gauged. Some had poorly developed particle ideas. Others did not
conserve mass in chemical reactions, or confused mass and density. Many showed poor
understanding about acids, combustion and dissolving. Although respondents knew
about single and double bonds, many seemed unaware that covalent bonds involve
electrons being shared. They found ionic bonds difficult to describe. Students did not
know that energy is released when bonds form.
Two further surveys of 320 students were carried out. 250 students followed the
Salters' Advanced Chemistry (SAC) course which adopts a context-led approach. Their
understanding of most chemical ideas probed changed by the third stage, although some
weaknesses were still apparent. The changes in responses observed in 70 non-Salters
and a sub-sample of 70 SAC students suggest that different approaches produce some
similar effects. The findings indicate that A level courses should include strategies for
teaching basic chemical ideas and highlights areas for further development of SAC.