“Regulating pH in fish-holding tanks” – teacher guide
Abstract
This task is designed for lower secondary students of 14-15 years old, or for upper secondary students of 15-16 years old, depending on each national curriculum. It is related to the concept of pH and its variations in a solution. It makes apparent the applications of chemistry in a real life situation. The activity becomes meaningful when students are getting involved in an inquiry based and a collaborative learning process, as the context can be open.
It is considered important that teacher provides all the necessary information and guidance, as the concept of pH is difficult and is usually taught in a traditional way.
It is designed for one to two hours depending on how open the teaching design will be.
The task
One of the most common problems encountered in establishments of fish hatcheries is to maintain a constant pH level in the fish-holding tanks. Through the video (link given below), students are introduced in the world of work in such an establishment and watch a worker who monitors pH in fish-holding tanks. Then, students have to figure out methods and appropriate actions to maintain a constant pH in fish-holding tanks. By working with this task, students can also obtain experiences in appreciating other factors related to the characteristics of each specific case in terms of economic and environmental issues.
Link to the video:
Goals
The task aims:
- To support students’ understanding of the concept of pH changes in a solution. Moreover, the meaning of pH for one specific case of world of work, like the well-being of fish and growth in the tanks of fish hatchery, is emphasized.
- To develop students’ ability to argue for necessary actions in order to keep pH level in the range of normality (CO2 is produced by the respiration of fish)
- To trigger students’ thinking of fish hatcheries issues under an economic and environmental perspective.
Finally, it aims to develop students’ awareness of the value of science, and more specifically, chemistry in the work places.
Lesson plan example
10-20 minutes: introduction of the problem through a video, discussion of the aspects of the problem.
15-30 minutes: groups of students work on the problem of the worksheet.
10-20 minutes: groups present their ideas and participate in whole class discussion arguing for the best solution
10-20 minutes: Reflections, conclusions and completion of the worksheet
The plan could also utilize selected sites or texts from sites with information concerning economic and environmental issues (indicative sites are suggested in the information sheet).
Teaching notes
The basic reason of pH changes in solutions isthe absorption of oxygen and the release of the CO2 during the process of respiration of fish. Fish absorbs oxygen and expulses carbon dioxide from the blood. Carbon dioxide is produced by fish during respiration and dissolves in water to form carbonic acid, thus lowering the pH.
The main goal is to decrease the quantity of CO2 that exists in the water of fish-holding tanks, or to “neutralized” the action of the produced CO2.
There are also other products from the biological processes of fish, which are important factors and are controlled by people working in fish farms. However, this activity does not take into account these products as the problem would become much more difficult.
The concept of acid oxides, as well as the buffer solutions may not be part of the curriculum for 14-15 years old students; so it is not suggested for this grade to explain and reason the phenomena on the basis of the relevant reactions. Probably with the older students, of 15-16 years old or more, these reactions can be brought in the foreground.
Three main methods can be used for the regulation of pH:
- Change of water in fish-holding tasks. This is suggested when the installation is close to the sea, because this method may be costly. This could happen even without pumps, in case there is a difference in attitude and so we can take advantage of the natural flow of water.
- ‘Breaking’ of the water. A process of pumping the water upwards (like a fountain), in order CO2 to be removed, while the quantity of O2 to be increased.
- Use of chemicals. Substances with weak base properties, like sodium carbonate and acid sodium carbonate can be used in order pH to be reduced (neutralization reactions).
Similar idea could be applied for the development of tasks concerning fish transportation, or aquariums.
The task is based on the idea of V. Amariotakis, a chemist teacher following Mascil, and is enriched and finalized by V. Spiliotopoulou of the Greek Mascil team.
CC BY-SA mascil consortium 2014
The mascil project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 320693