CORAL CAM LESSON PLANS
CREATED BY THE TEACHER ADVISORY GROUP

Coral Cam Web Site

Water Salinity                                       Mr. Cesare Filice

OBJECTIVE:   To determine the salinity of different samples of water using a 
                               variety of methods. 

BACKGROUND

Corals require a relatively constant environment.  However, due to their 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. 

Here we will investigate different methods that we can use to determine the salinity of water samples. The SeaTest measures specific gravity and provides students with the concentration of dissolved salts (ppt).  Conductivity provides students with a measure of salinity based upon the amount of current that is able to flow through the solution.  The colourimteric determination provides students with a measure of salinity using a simple titration and colour chart.  (please note that titrations are still used to calibrate many apparatus.)  After these different determinations students can compare the results of these methods. 

MATERIALS

    Aquarium Systems SeaTest (available from your local pet shop)

    Conductivity meter (eg. Keltec Soluble Salts Analyser)

    Colourimetric Salinity Test Kit                          salt (table, sea salt, aquarium salt)

    6 x 250 ml beakers                                          100 ml graduated cylinder

    scale                              glass rod                     wax pencil

PROCEDURE

1.Using the wax pencil, label the beakers 0%, 1%, 2%, 3%,4% and 5%. 

2.Using the graduated cylinder, measure 100 mL of water and pour it into each of the 250 mL beakers. 

3.Set aside the beaker of water labeled 0%. 

4.Measure 1g of salt and dissolve in the beaker labeled 1%.  Stir the mixture with the glass rod until all of the salt is dissolved. 

5.Repeat step #4 with each of the other appropriate beakers using 2g, 3g, 4g and 5g of salt. 

6.Take a sample of the plain water from the 0% beaker and measure the conductivity and record your data in table form. 

7.Pour the sample back into the originally beaker. 

8.Pour the water into the SeaTest apparatus.  Be careful not to trap bubbles.  If bubbles are present tap the side of the container to remove them. 

9.Record the salt concentration of the solution.  Note: For 0% it is not readable. 

10.Using the Colourimetric Salinity Test Kit take a sample of the 0% solution and add the appropriate reagents.  The water will then change colour. 

11.Compare the final colour of the solution with the colour chart provided to determine the salinity of the solution. 

12.Repeat steps 6 - 11 for each of the 5 solutions. 

13.Students can plot the data (conductivity vs. concentration; specific gravity vs. concentration; parts per thousand vs. concentration) 

14.Students can interpolate their curves to find values corresponding to 35 ppt and 37 ppt. 

15.Students can discuss the pros and cons of each method and who the results for each solution compare among the different methods used. 

Results: 

                           SALINITY DATA TABLE        

Percent                  Conductivity                 SeaTest Apparatus                     Colourimetry    
Solution                  mOhms     ppt                    SG     ppt                              Colour     ppt

0                                            
1                                            
2                                            
3                                            
4                                            
5                                             

EXTENSION

Have students bring in samples of water from their homes and their surrounding areas.  The salinity of these samples can be then be measured and compared.

© BBSR and TCOE Coral Web Site Team 1999      http://www.coexploration.org/bbsr/coral
Funded by a grant from the Goldman Foundation