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Grade(s): 6-7
Introduction: Corals require a relatively constant environment. However, due to the proximity to the surface of the ocean, the salinity of the water may change with precipitation. The water, around Bermuda has a salinity of 37 parts per thousand. In contrast, most of the Atlantic Ocean has a salinity of 35 parts per thousand. In the fall and winter months the amount of precipitation increases significantly, and as a result, the salinity of the water surrounding Bermuda decreases especially around the shoreline due to runoff. Corals can tolerate some variation in the salinity of their environment.
In this activity, students will investigate different methods that they can use to determine the salinity of water samples. The Sea Test measures specific gravity and provides students with the concentration of dissolved salts (parts per thousand or ppt). Conductivity provides students with a measure of salinity based upon the amount of current that is able to flow through the solution. The colourimetric determination provides students with a measure of salinity using a simple titration and color chart. Once these different determinations are completed, students can then compare the results of these methods.
Learner Objective(s):
- The student will be able to determine the salinity of different samples of water using a variety of methods.
- The student will be able to describe the chemical properties of water.
- The student will be able to explain differences between salt water and fresh water.
Florida Sunshine State Standards: Science: SC.A.1.3.1/ SC.A.1.3.4 Math: MA.B.3.3.1
Competency Based Curriculum: Science: M/J-3-III-2-A Math: M/J-I-III-2-A; Math: M/J-3-II-9-B
Materials:
Aquarium Systems Sea Test (available from local pet shop)
Conductivity meter (i.e., Keltec Soluble Salts Analyzer)
Colourimetric Salinity Test Kit
Six 250 ml beakers
100 ml graduated Cylinder
Glass rod
Wax pencil
Salt
Scale
Activity Procedures:
- Using the wax pencil, label the beakers 0%, 1%, 2%, 3%, 4%, and 5%.
- Using the graduated cylinder, measure 100 ml of water and pour it into each of the 250 ml beakers.
- Set aside the beaker of water labeled 0%.
- Measure 1 g of salt and dissolve in the beaker labeled 1%. Stir the mixture with the glass rod until all of the salt is dissolved.
- Repeat step #4 with each of the other appropriate beakers using 2g, 3g, 4g, and 5g of salt.
- Take a sample of the plain water from the 0% beaker and measure the conductivity (use the conductivity meter) and record your data in table form.
- Pour the sample back into the original beaker.
- Pour the water into the Sea Test apparatus. Be careful not to trap bubbles. If bubbles are present, tap the side of the container to remove them.
- Record the salt concentration of the solution. Remember: 0% is not readable.
- Using the Colourimetric salinity Test Kit, take a sample of the 0% solution and add the appropriate reagents. The water will then change color.
- Compare the final color of the solution with the color chart provided to determine the salinity of the solution.
- Repeat steps 6-11 for each of the 5 solutions.
- Students can plot the data (conductivity vs. concentration; specific gravity vs. concentration; ppt vs. concentration)
- Students can interpolate their curves to find values corresponding to 35 ppt and 37 ppt.
Student Assessment:
Allow student to answer critical thinking skills questions assigned by the teacher.
- Is it easier to float in salt water than fresh water? Explain.
- Discuss the pros and cons of each method used in the activity and how the results for each solution compare among the different methods used.
Ask student to interpret data plotted in step #13 of the Activity Procedures.
Activity Extension(s):
- Challenge students to create a model that demonstrates the increasing salinity of a salt- water solution as water evaporates (Chemistry).
- Design an experiment that tests the effects of reduced salinity on brine shrimp (Biology/Ecology).
- Calculate the percent of chloride in different solutions of water assigned by the teacher. (Math).
Home Learning Activity:
Allow students to bring in samples of water from their homes and their surrounding areas. The salinity of these samples can then be measured and compared.
Attachment: Salinity Data Table (completed during Activities Procedures)
|
% Colourimetry |
Conductivity |
Sea Test Apparatus |
Color |
| 0 |
1 |
1 |
1 |
1 |
| 1 |
1 |
1 |
1 |
1 |
| 2 |
1 |
1 |
1 |
1 |
| 3 |
1 |
1 |
1 |
1 |
| 4 |
1 |
1 |
1 |
1 |
| 5 |
1 |
1 |
1 |
1 |
Vocabulary: salinity, precipitation, conductivity, colourimetric, simple titration
References/Related Links:
www.educationworld.com
http://www.odysseyexpeditions.org/oceanography.html
http://seawifs.gsfc.nasa/OCEAN_PLANET/html
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