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  Investigating Conductivity
 

Conductivity is a measure of water's ability to conduct electrical current. Measurements of conductivity provide a general indication of water quality. The geology of a lake's watershed establishes the normal ranges for conductivity in a lake. Some pollution discharges and polluted runoff into lakes can cause changes in conductivity especially if the pollutants include inorganic dissolved solids such as ions: bicarbonate, sulfate, chloride, calcium, magnesium, sodium, potassium, and phosphate.

You have been hired by a chemical company suspected of discharging pollutants into a WOW lake during the summer. You need to determine whether or not charges against the company are accurate. One of the variables to be analyzed is conductivity. You need to explain conductivity to company executives prior to investigating actual lake data.

Part I - Conductivity in the Laboratory

Knowledge Base
As an introduction to your presentation, write a paragraph that explains how conductivity relates to lakes and how pollutants in lakes may affect conductivity.

Experimental Design
The following equipment is available in your lab:

  • a hot water bath for samples
  • conductivity pen (or other conductivity meter)
  • five 50 ml beakers or small clear glasses
  • a squirt bottle filled with distilled water
  • a thermometer or temperature probe

The company has asked you to analyze the conductivity of tap water, tap water with baking soda, tap water with table salt, tap water with granite chips, and tap water with nitrate-rich fertilizer. Describe how you will set up a laboratory experiment to test these samples. Predict which samples will have the highest and lowest conductivity readings and record your predictions.

Data Collection
Create a table or form to record your measurements. Then test the samples at room temperature and record the data. Next, place the samples in a hot water bath until the samples have increased in temperature by 10 degrees. (Rinse the thermometer each time it is used to check the sample temperature.)

Data Management and Analysis
What variables might have affected your results? If the executives are not sure that your data are accurate, how could you prove your results are valid?

Interpretation of Results
How might these readings relate to conductivity readings in lakes?

Data Presentation
You need to use your introductory paragraph and other items recorded in your lab journal in your final report. Your instructor will specify the format for the final presentation: written paper, oral report, poster, or multi-media presentation.

Part II - Investigating Conductivity in a Lake

Knowledge Base
Reflect on what you know about conductivity in laboratory water samples. How might this relate to the WOW lake on which the chemical company is located? If there were not pollutants involved, would you expect to find lake conductivity measurements similar to those found in the lab? Why?

Experimental Design
Identify the WOW lake the chemical company is having you investigate. Predict which depths would have the highest natural conductivity measurements. Explain the rationale for your predictions in your lab journal.

Describe how you will collect and use the WOW data to resolve the charges against the chemical company. (Your description should include answers to questions such as: What data will you collect? How many days' worth of data should you use?)

Data Collection
Make sure you have a table or system set up for recording your data. Then access the conductivity data for the WOW lake from the website.

Data Management and Analysis
What will be the best way to organize your data for analysis? Would it be useful to create a graph of the conductivity rankings for the lake?

Interpretation of Results
Your final report must address the following questions:

  • What might cause the conductivity readings to vary within different layers of the lake?
  • What are the relationships between time of year and conductivity values?
  • Is it reasonable to suspect lake pollutants based on conductivity measurements?

Reporting Results
Use the data from your laboratory study and WOW to create a presentation for the chemical company. It can be an oral presentation, written paper, poster, or multi-media presentation. If you have determined that chemical pollution of the lake has occurred, include suggestions about how to mitigate the problem.

 


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date last updated: Friday October 08 2004