Development and application of a diagnostic instrument to evaluate secondary school students’ conceptions of electrolysis

Abstract

A two-tier multiple choice diagnostic instrument consisting of 17 items was developed to evaluate students’ understanding of basic electrolysis concepts. This study which used mixed qualitative and quantitative methods, was conducted in 2006 and 2007 to produce the final instrument. Subsequently, the final instrument was administered to 16 year-old secondary school students (N = 330) who had completed the first year of a two year chemistry course. The instrument was found to have a high Cronbach’s alpha reliability coefficient of 0.85 which is greater than the threshold value of 0.5 quoted by Nunally and Bernstein (1994). Analysis of students’ responses demonstrated good discrimination indices between the top and bottom groups of low- and high-achieving students, with the indices ranging from 0.42 to 0.84 for 16 items and 0.28 for one item. The analysis also identified 29 alternative conceptions that involved a variety of electrolysis concepts relating to the nature and reaction of the electrodes, the migration of ions, the preferential discharge of ions, the products of electrolysis, and changes in the concentration and colour of the electrolyte.In addition, there was a mismatch between students’ confidence in answering the items and their correct responses. Students’ level of confidence in providing correct responses to these items ranged from 44% to 72%, but the actual correct responses ranged from 19% to 53%. As no other similar instrument has been reported in the research literature, this instrument is a convenient diagnostic tool that teachers could use to identify students’ preconceptions prior to introducing the topic. In addition, using the instrument in formative assessment during classroom instruction will enable teachers to identify students’ alternative conceptions and institute appropriate remediation measures with the students concerned.