Experiences

Salt hydrolysis – theoretically and practically

Ilze Kupše

Latvia

Vocational School

Chemistry

Teaching in class

Direct

Topic “Electrolytic dissociation” is included in the acquisition of the Chemistry course of form 10. Salt hydrolysis is taught speaking about the electrolytic dissociation. For many years this topic causes difficulties to my students. That is why when I am teaching this topic I am trying to combine theoretical questions with practical activities.
Salt hydrolysis – reaction of the positive salt metal ions or negative acid remainder ions with water molecules in result of what free hydrogen ions or free hydroxide ions can develop and acidity of liquid environment can change.
In order students could learn this topic more successfully, I have divided learning process and layout of the topic in several parts:
1. Revision of universal indicators, idea and suitable environment of the pH,
2. Revision of the theory on electrolytic dissociation, strong and weak electrolytes, degrees of dissociation,
3. Explanation of the salt hydrolysis process, calculation of the exercises.
Revision and discussion of the questions have big meaning in the successful learning of the topic. I start to discuss the questions with the topic - indicators. During the lesson we revise what is “indicators” and their types. One the most popular and often used indicator is universal indicator. During the lesson colour range of the universal indicator is given to the students, in order that each student could see the division of the universal indicator colour range and corresponding environment. We also discuss the idea – pH of environment, corresponding colouring and environment. Using real examples we discuss where pH is used in daily life and find out the meaning of pH in different types of products.
Then I revise topics – dissociation process, degree of dissociation and electrolytes. Quite big difficulties are caused to students by the writing of dissociation equation. We revise the writing of acid and base dissociation equation. Students make the table where acids and bases are divided in two groups – strong and weak electrolytes. It helps them to understand the process of salt hydrolysis. When all the questions on the indicators, dissociation process are revised we can start to study options of the salt hydrolysis process (total hydrolysis, cation and anion dissociation does not take place).
Explanation of the topic “salt hydrolysis” I start with the examples of salt liquid hydrolysis when total hydrolysis takes place or the example of salt liquid hydrolysis when the process does not take place. I simulate the students to use their own prepared table of strong and weak electrolytes so the topic would be studied more completely. I plan laboratory work for the next lesson so each student could learn salt hydrolysis process also during the experiment using knowledge that is already learned theoretically. During the laboratory work I divide students into the groups of two. Each group has to examine theoretically and during the experiment 5-7 salt liquid hydrolysis examples. They have to find out the pH of hydrolysis process environment with the help of universal indicator. Looking at the salt hydrolysis process theoretically and practically student gains more detailed knowledge in the study of the topic.
Already many years I use practice – during the teaching students the process of salt liquid hydrolysis - to check theoretical knowledge practically. It develops research skills in the students as well as it helps to learn the topic more detailed.