This study aims to produce a guided inquirybased salt hydrolysis module to improve students' critical thinking skills by determining the level of validity, practicality and effectiveness of the module. The type of research used is research development or Research and Development (R&D). The sampling technique uses cluster purposive sampling. The number of samples is 57 students from both schools. The development model used is the Plomp development model which has three stages namely the initial investigation phase (preliminary research phase), the prototype phase (prototyping phase) and the assessment phase (assessment phase). The research instruments used were interview sheets, questionnaires in the form of validation and practicality sheets, objective questions, and critical thinking questions. Data analysis techniques using SPSS 16 software. The results obtained by N-gain experimental class is higher than the control class that is experimental class 1 and 2 have N-gain 64.65 and 59.46, while control classes 1 and 2 have N-gain 60 , 83 and 58.6 with significant differences. Hypothesis test results show a significant difference between the critical thinking skills of the experimental class and the control class, both in schools with high and low student abilities.

Keywords : modules, salt hydrolysis, guided inquiry,Critical thinking, Plomp Development