The “Emil Racovita” Secondary School in Galatzi, Romania has carried out a laboratory chemistry activity on acid-base indicators.
Aura Cozmaciuc, the chemistry teacher, and her 16 and 17 year-old students have used the Heureka colourful activity available both on the Xplora portal and on the Xplora Knoppix DVD.
The main aim of the activity was to familiarise students with the acid-base indicators and to let them understand the importance of these indicators in featuring the environment.
Lesson type: laboratory workshop
• to define acid-base indicators;
• to classify acid-base indicators;
• to perform some experiments and to indicate the environment reaction using acid-base indicators.
• to understand the importance of those substances
Learning approaches used:
-controlled or independent discovery;
-Heureka colourful chemistry lesson, from the XPLORA Knoppix DVD and from Xplora portal.
Lesson set up:
a) Organizational moment: 2 minutes
- writing down the absent students in the class register;
- creating the right atmosphere for didactical activities;
b) Knowledge evaluation: 10 minutes;
-verifying the homework given to students;
-verifying the comprehension of the previous lessons “Acids and bases”, through some questions:
• What are acids?
• Which are their main characteristics?
• How do they color acid-bases indicators learned in previous classes, such as litmus and fenolftalein?
• The same questions will be asked for base indicators.
• Which is the name of the reaction between acids and bases? Which substances are obtained following this reaction?
• Gives examples of substances used at home that have acid or basic characters.
• Yogurt, orange and lemon juice taste sour. Which characteristics do you think they have?
c) Learning new knowledge: 30 minutes ;
This phase starts with the announcement of the new lesson “Acid-base indicators” which will be written on the blackboard.
What is an indicator?
It is a substance with organic molecule, which changes colour depending on the pH. In a pH field will coexist species of both acid and basic characters in comparable concentrations. On this field, the colour will be given by the mix between acid and basic species. In order not to influence the pH of the studied substance, the indicator quantity to be used, has to be very small. Download the full lesson plan (pdf, en).