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In this article is presented a gradual path on the pH making use of the laboratory. The idea arises from the consideration that the laboratory does not have to be the place of the ritual repetition of standardized procedures, often carried out with materials and instruments prepared, but a method of approach to phenomena and situations that promote the active participation of students. We move from a qualitative measure of the pH of acidic solutions, basic and neutral, to quantitative measure of the equivalent point of an acid-base titration. The methodology used by the teachers is based on learning by doing: few notions of theory to learn the fundamental concepts and many laboratory activities that help the students to produce reports on their activity. The qualitative measurement of pH, using as an indicator the red onion of Tropea (Italy), was carried out in a lower secondary school, while the volumetric analysis has been at the center of lab activity addressed to fourth class of a technical institute. In particular, the attention has been focused on acid-base titrations and how to determine the equivalence point. In both school levels, the primary objective was the acquisition of the fundamental principles and practical skills relating to the methods of analysis. All activities have been selected and organized in order to constitute a valid and mutual integration with the theory, not only as a moment of experimental verification of what the students have learned in theory, but also, where possible, as a basic tool to derive laws, principles theoretical models starting from the experience.

Pectin is extracted from plant residues frequently available as by-product of economically more valuable food processing and is widely used for different applications. In industrial process, separation of the hydrolysed pectin solution is performed by centrifugal and filtration technologies. In this paper, the effect of water addition to the hydrolysed citrus peels slurry on the separation efficiency was investigated, with the aim to improve pectin recovery. Different dilution ratios were tested and it was found that the pectin recovery increases when increasing water addition passing through a maximum value. No relevant effects on pH and pectin yield were found when increasing the contact time between water and hydrolysed slurry, confirming that no further progress of hydrolysis or extraction processes is caused by the dilution. Therefore, the increase in pectin recovery can be attributed only to the water addition.