Download *Regulating pH in fish-holding tanks* * teacher guide

“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:
https://onedrive.live.com/redir?resid=2BC277A7AE32D507!38782&authkey=!AGIalFqWDudm
asM&ithint=video%2cwmv
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
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 320 693
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 is the 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.
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 320 693
Three main methods can be used for the regulation of pH:
1. 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.
2. ‘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.
3. 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 320 693