Materials:
1 meter stick, glass tubing, rubber tubing, thistle tube, 2 clamps, ring stand, water, salt.
Procedure:
-
1. Bend a piece of glass tubing into a Ushaped manometer tube with arms equal.
-
2. Support the manometer with a ring stand and clamps. (see diagram below).
-
figure available in print form.
-
3. Pour water into tube until it is half full.
-
4. With the rubber tubing, connect the thistle tube to the manometer. Keep it out of water.
-
5. Read the levels at A and B with a meter stick.
-
6. Keep a record of readings with the thistle tube in the air, and at varying levels down the water cylinder.
-
7. Make a scale and plot the data as depth versus pressure
Questions:
-
1. What would be your readings if you substituted salt water for fresh?
-
2. Make a comparative table of the same kind of data as in procedure #6.
Activity 3—
How
You
Measure
the
Salinity
of
Seawater
?
-
To Make a Hydrometer
Materials:
2 pencils, baby jars or beakers, metal weight or a metal nut, and string.
Procedure:
Tie a weight to a pencil, or screw a pencil into a metal nut
Fill a onequart bottle with tap water
Float the pencil in the water.
Observe the level to which it sinks.
Mark it off with a notch.
Repeat this experiment in a container of salt water.
figure available in print form.
Questions:
-
1. Is the water line on the stick different in salty and fresh water?
-
2. What do you think causes the difference?
-
3. Get a marked unknown (to you) concentration of a salt solution. Can you guess the salinity of this solution? Compare with a hydrometer.
-
4. Which is more dense, salt or fresh water?
-
5. Can you design an experiment to prove or disprove your hypothesis?
Activity #4—
Pollution
Concept
: Pollutants may slow down or destroy all life.
Information
: The difference between life and death for most organisms is the availability of oxygen. Aquatic animals must have their oxygen dissolved in water to be used for respiration. The concentration of dissolved oxygen in an aquatic environment is a significant measure of its ability to support life.
The amount of dissolved oxygen (abbreviated DO) varies with temperature and the salinity of the water and depth. The higher the temperature and the greater the salinity, the less oxygen will the water hold. A low DO content indicates low water quality due to pollution and high temperatures.
Dissolved oxygen can be measured qualitatively and more accurately, quantitatively. Methylene blue can be used qualitatively as a method of measurement. Qualitative methods such as measuring, by titration and recording the amounts of dissolved oxygen by converting the number of drops of a chemical (sodium thiosulfate) needed for a color change.
For those who do not want to make up solutions and reagents, there is a dissolved oxygen kit available from the Hach Chemical Company (P.O. Box 970, Ames, Iowa, 50010).
Objectives:
At the completion of this learning experience, the student will be able to:
-
1. Determine qualitatively the presence of dissolved oxygen by using the methylene blue method.
-
2. Recognize the relationship between water quality and dissolved oxygen.
-
3. Recognize the relationship between the types of plants and animals living in the water and the amount of DO present.
Determination of DO by the Methylene Blue Method
Materials:
4 test tubes
250 ml beaker for test solution
250 ml beaker for methylene blue solution
tap water
water samples
test tube holder
test solution
methylene
blue solution
To make the test solution, heat 8 grams of KOH in 300 ml of water. Cool and stir in 10 g of dextrose (glucose). To make the methylene blue solution, mix 0.25 grams methylene blue in 100 ml water.
Procedure:
-
1. In one test tube, put 5 ml of tap water and 5 ml of test solution. Add one drop of methylene blue solution and mix gently.
-
a) What color is it? ____________________ Let the solution stand in test tube rack.
-
b) How long does it take for the color to disappear? _________________ Stopper the test tube and shake for 30 seconds.
-
c) What is the color of the water? _______________________ Let sit in rack. How long does the color last? ___________
-
d) What gas was being added to the water by shaking it, do you think?
-
2. Pour your solution in the test tube back and forth between two test tubes for one minute to aerate the solution.
-
a) What happened to the color of the solution after oxygen was put back into it? Label this #
1
room
temperature
test tube and save it.
-
3. Pour 5 ml of tap water into two test tubes. Partially heat one and boil the other for 30 seconds. Add 5 ml of test solution to each test tube. Then add one drop of methylene blue solution to each.
-
a) What color is the heated solution? _________________
-
b) The boiled solution? ___________________________________
-
c) If either blue, how long does the color last ?__________
-
d) Why doesn’t the color last as long as it did in procedure #1______________________________________
Shake all three solutions,
the room temperature
, the
heated
, and the
boiled
, for 30 seconds.
-
a) Which one does the color last the longest? _____________
-
b) Which one does the color last the shortest? ____________
Now you know what can determine the amount of oxygen present in some samplings. If you want to measure dissolved oxygen by this method, it is necessary to do the test at the sampling site.
Measure 5 ml of the saline into a test tube. Add 5 ml of the test solution and a drop of methylene blue solution. Shake the test tube once to distribute the methylene blue throughout the solution. How long does the blue color last in each sample? Record your results in the second column of the table below. In column 3, Relative Amount of D) in Water. Assign the number 1 to the sample that had the most D) or longest reaction time, 2 to the sample with the next longest, etc.
Sample No.
|
Time of Color Reaction
|
Relative Amount
|
Source
|
|
Observation from
|
of D) in water
|
of water
|
Questions:
-
1. Did you test any samples of polluted water? _____________ What did your test show about the dissolved oxygen content of the sample? ____________________________________________
-
2. What gas is lacking or in reduced amounts in organically polluted water? ___________________________________________
-
3. How do you think living organisms are affected living in that water? _______________________________________________
Conclusion
:
Look again at Fig. 2, Map of New Haven Harbor in 1939. Where is I95 located? No, not there. Man had to rearrange the contours of the waterfront to make land available. What ecosystems were disturbed?
In order for the next generation to make valid decisions concerning their environment, they must be made aware of the consequences of poor judgment or apathy. Too many wrong decisions could totally upset the balance of nature that is so delicate. Non renewable resources are being used up with no way to replenish them. Technology has shown us ways to harvest many things from the sea, but we must examine carefully its place in this ecosystem, where there is a great interlocking web of dependency. Above all, we must protect the producers of our greatest source of lifegiving oxygen, the photosynthetic processes carried on by those tiny plants of the sea, the phytoplankton. Not only do they insure the quality of our life but they are the big food producers of all sea animals.
It is hoped that by learning and becoming a little more interested in the sea and all that is in it and all that surrounds it, we will have the desire to always protect it. This can only be accomplished by a knowledgeable, sensitive group of people.