The purpose of the study was to establish a relationship between the shift of meaning of the concept oxidation that has taken place during the historical development, and students' alternative concepts. First Examination Board papers were examined. The result enabled us to specify the research question. In the main part of the study, multiple-choice items were given to 3074 senior high school students. They were asked to select the correct answer and to justify their choices. Additional illustrative material was collected in four interviews with senior high school students. The analysis of the data revealed the mechanism that some students used to interpret the reactions from NO[subscript 3][superscript -] to NO and from CO[subscript 3][superscript 2-] to CO[subscript 2]. Students' interpretations were based on the concept of a transfer of oxide ions. The mechanism explains some correct and incorrect answers to the problems. The interview study also revealed that students were reluctant to accept water as a "Bronsted base". It is suggested to use students' alternative concepts about oxidation reactions in class, helping them to better understand the "half-reaction method". Students should also understand that the meaning of the concept oxidation has shifted in the course of time. In the area of "acid-base reactions", further research is needed. (Contains 2 tables and 2 figures.)