Problem Based Learning Using the Water Quality Evaluation to Teach Acid-Base and Solutions Concepts

The results of the National System of Basic Education Assessment (Saeb) in 2017 indicate that high school has contributed little to the cognitive development of Brazilian students. In Chemistry, a way to improve this situation is the application of methods that integrate theoretical concepts to the daily lives of students. This work used the Problem Based Learning method to teach acid-base theory and solutions using the water quality as a contextualizing theme. Based on the chemical concepts inherent to the water disinfection process and the importance of the issue regard to its quality, two chemical parameters of the potability of the water consumed in Colegio Estadual Professor Alfredo Balthazar da Silveira and in areas close to the school were investigated. The parameters were the chlorine content and pH. It was observed that the dynamics of experimental classes, together with the collect of water samples by students in their homes, led to greater engagement by the class, who left the spectator position of their learning, and became protagonist of the process. Regarding the results, all water samples showed pH within the range recommended by the Ministry of Health (MS). From eleven samples tested, two presented chlorine content according to the determination of MS, one of them was the cistern of the school. The other nine points showed chlorine concentration below the detectable limit by the colorimetric method of o-tolidine (<0.5 mg L-1), making it impossible to affirm if the samples are in compliance or not, in relation to the limits established by MS.