[ Secondary Science Instruction ]


What's in the Water?

Activities Using Computer Based Labs with Probes to Acquire Data




[ Temperature | pH | Dissolved Oxygen | Turbidity | Nitrates and Phosphates ]

Part B: pH

Overview/Introduction:

The pH scale is logrithmic and each unit is a tenfold difference in the concentration of hydrogen ions and hydroxyl ions. A molecule of water has one hydrogen ion, H+ and one hydroxyl ion, OH-. Equal concentrations of these two ions result in a pH of 7 which is neutral; thus, pure water is neutral.

An excess of hydrogen ions result in an acidic solution. The greater the number of hydrogen ions above hydroxyl ions the stronger the acid, which is indicated by a lower pH number. A solution with a pH of 2 is ten times stronger an acid than one with a pH of 3.

Likewise a pH higher than 7 indicates a base or alkaline solution. The higher the number the stronger the base.

The pH of bodies of water are affected by rainfall, pollutants, organisms that live in the water, human activity, and geologic factors such as limestone deposits and soil.

Many organisms living in bodies of water are sensitive to small changes in pH.

Purpose or Objective:

  1. To accurately measure and compare the pH of water samples from various sources.

Time Required: Less than one period

Materials, Tools, and Resources Needed: CBL, Graphing calculator or lap top, pH sensor, Cups or beakers (optional)

Teacher Preparation:

Collect water samples from local bodies of water.

Procedure:

Obtain samples of water from various sources:

  1. Tap water from well and aqueduct sources

  2. Water from alkali lakes, stream fed lakes, ponds or hot springs. or

  3. Water from upper, middle, and lower reaches of streams or rivers

    Measure and record pH of each sample.

Procedure for CBL (see CBL manual for complete instructions):
  1. Connect the pH sensor into the CBL interface. Use the link cable to connect the graphing calculator or lap top to the interface.

  2. Turn on the calculator or lap top and start the data program.

  3. Rinse the pH sensor with distilled water. Place sensor tip into a buffer solution with a pH of 7. Wait for the voltage to stabilize and enter "7".

  4. Rinse the pH sensor with distilled water. Place sensor tip into a buffer solution with a pH of 10. Wait for the voltage to stabilize and enter "10"

  5. Set up the data collection mode.

  6. Rinse the pH sensor with stream water. Place the tip of the pH probe to a depth of 3-4 cm for 30 seconds and select START to begin the operation. Keep in place for 10 seconds.

  7. The pHvalue will appear on the screen after 10 seconds.

    Repeat steps 3-4 for additional sites and samples.

    Rinse the pH sensor with distilled water and return it to the storage bottle.

Student Handouts/ Record Sheets

  1. Data chart

Student Discussion Questions:

  1. How does the pH of the water in each grouping compare with others in the group?

  2. How do the abundance and activities of living things affect the pH of water habitats?

  3. How does decomposition affect the pH?

  4. How does the geologic substrate affect the pH?

Grade 9-12

California Science Content Standards

Acids and Bases

5. Acids, bases, and salts are three classes of compounds that form ions in water solutions. As a basis for understanding this concept:

  •  
    		•  Students know the observable properties of acids, bases, and salt solutions.

  •  
    		•  Students know acids are hydrogen-ion-donating and bases are hydrogen-ion-accepting substances.

  •  
    		•  Students know how to use the pH scale to characterize acid and base solutions.

    Solutions

    6. Solutions are homogenous mixtures of two or more substances. As a basis for understanding this concept

  •  
    		•  Students know the definitions of solute and solvent.

  •  
    		•  Students know how to calculate the concentration of a solute in terms of grams per liter, molarity, parts per million, and percent compositions

    Ecology

    6. Stability in an ecosystem is a balance between competing effects. As a basis for understanding this concept:

  •  
    		•  Students know how to analyze changes in an ecosystem resulting from changes in climate, human activity, introduction of nonnative species, or changes in population size.

  •  
    		•  Students know how water, carbon, and nitrogen cycle between abiotic resources and organic matter in the ecoystem and how oxygen cycles through photosynthesis and respiration.

    Investigation and Experimentation

    Scientific progress is made by asking meaningful questions and conducting careful investigations. As a basis for understanding this concept and to address the content in the other four strands, students should develop their own questions and perform investigations. Students will:

    a. select and use appropriate tools and technology (such as computer-linked probes, spreadsheets, and graphing calculators) to perform tests, collect data, analyze relationships, and display data.

    National Education Technology Standards for All Students

    3. Technology productivity tools

    Students use technology tools to enhance learning, increase productivity, and promote creativity.

    Technology research tools

  •  
    		•  Students use technology to locate, evaluate, and collect information from a variety of sources.

  •  
    		•  Students use technology tools to process data and report results.

  •  
    		•  Students evaluate and select new information resources and technological innovations based on the appropriateness to specific tasks.

    Technology problem-solving and decision-making tools

  •  
    		•  Students use technology resources for solving problems and making informed decisions.

  •  
    		•  Students employ technology in the development of strategies for solving problems in the real world.

     

     

     

     

     


    The Integrating Technology into Science Instruction webpages project is partially funded by grants from The Boeing Company and The Ralph M. Parsons Foundation. Integrating Technology into Instruction is a project of Target Science (target@laep.org) and is displayed on the Los Angeles Educational Partnership Learning Exchange. Target Science is an initiative of the Los Angeles Educational Partnership.
    Updated August 2000