The purpose of this research was to find out how students’ needs of 3TMC diagnostic test to measure students’ conception about acid-base and solubility equilibrium. This research was a qualitative study. The research population were 96 students in 4 senior high school. This research used random sampling technique. Data gathering used non-test method by using questionnaire with 10 questions. The results showed that 96.9% of students stated that the development this instrument is needed. In addition, there were several problems obtained in this questionnaire include: learning activity, teacher’s test and guessing.  In conclusion, this it necessary to develop the 3TMC instrument that can diagnose and measure the student conception in acid-base and solubility equilibrium.