How Much Dissolved Oxygen is in the Water?
Students will be ask to bring water sample from different watershed near their house. They will learned how important is dissolved oxygen to different  water creatures available in the laboratory using titration. They will convert the titration data to ppm or mg per liter in order to compare their data to the standard value for a water creatures to successfully survive.
 
Objectives
Students will
a.) learned how important dissolved oxygen for water creatures
b.) calculate titration data and be able to convert the unit of titration to mg per liter
c.) compare the calculated data to the standard data
Materials
  Worksheet for Monitoring Dissolved Oxygen Using Different Watershed
Procedure
Water Sampling Precedure :
1.) Students will bring three different water samples for each group.
2.) Students will follow this water sampling  procedure:
a.) Use a clean 500 ml mineral water bottle with cap and immerse the bottle about one foot the surface of the body of water being sampled. Allow the water to enter the bottle until it is completely filled.
b.) Put back the cap on the bottle while still immersed below the surface. Gently lift the bootle out of the water avoiding unnecessary agitation.
c.) Analyze the dissolved oxygen  (DO) right away. If it is not possible store the sample in a refrigerator and protect from sunlight.
d.) Note the sampling location, the time of collection and other conditions during sampling.

Monitoring Dissolved Oxygen:
1.) Students will take 25 millimeter of titrant, sodium thiosulfate with 0.025 M concentration, and put it into a buret. Using a buret clamp, clamp the buret to an iron stand.
2.) Open the sample bottle with great care and dip a glass pipet containing 5ml of MnSO4 solution. With the tip of the pipet, halfway of the water depth, release the contents of the pipet.  The addition of MnSO4 will cause an overflow of the water sample).
3.) Add 5ml NaOH-KI at once in a similar manner as in (2). Close tightly the bottle immediately and mix the contents thoroughly by making  2 rapid inversions of the bottle in the hand. Let the bottle stand for a few minutes to allow the precipitate to settle. Do not proceed to the next step untill all the precipitate has settled down.
4.) Remove the cap and add 5 ml of concentrated H2SO4 using glass pipet in the same manner as before. Close the bottle immediately after the acid is added, shake the bottle and allow to stand for a few minutes untill all precipitate has completely been dissolved.
5.) Place about 200 ml of the sample water in the Erlenmeyer flask and add 3 ml of 1 % starch solution. Titrate the sample with standard sodium thiosulfate untill the solution becomes colorless. Record the volume of the sodium thiosulfate used.
6.) Start putting the data into the provided formula. (see the worksheet provided)
7.) Students will be getting a unit into mg per liter and compare in to the standard value of 5 mg per liter for most likely water creatures successfully will survived.
References
1.) Winkler Method
2.) Lab manual for General Chemistry of Mapua Institute of Technology, Phils. Authors Mrs. Edna Calderon and et.al.
State Standards
1.2.3- The student will formulate a working hypothesis.
1.3.1- The student will develop and demonstrate skills in using lab and field equipment to perform investigative techniques.(NTB)
1.3.2- The student will recognize safe laboratory procedures.
1.3.3- The student will demonstrate safe handling of the chemicals and materials of science.(NTB)
1.4.2- The student will analyze data to make predictions, decisions, or draw conclusions.
1.5.2- The student will explain scientific concepts and processes through drawing, writing, and/or oral communication.
1.7.1- The student will apply the skills, processes, and concepts of biology, chemistry, physics, and earth science to societal issues.
Lesson Resources