Measuring the Nitrate concentration of your samples?

May 26, 2006

Objectives:

 Students will be able to:

Determine the nitrate value for each of their 7 samples.

Note: Safety goggles should be worn at all times during this lab activity.

 

Materials:

7 water samples

7 small beakers (100 mLs)

Paper towels

Pipettes

 

Procedure:

1. Obtain a box containing a Nitrate Ion Selective Electrode and Nitrate standard solution.
2. Set up and connect LabWorks interface with the laptop.
a. Press “esc” key when asked for a password on the laptop.
b. Make sure the probe is connected to slot 1.
3. Using the 1000 ppm standard provided make 100 mL solutions of 500 ppm and 100 ppm standards. Check with the TA if your calculations are correct before you make the solutions.
4. Open up the lw.exe program by double clicking the icon on the desktop.
5. Under the file menu, choose open.
6. Find and open the nitrate.exp file.
7. Press the Calibrate button.
8. Scroll all the way to the bottom of the list provided and select the one called Nitrate.
9. Click Calibrate
10. Click next
11. Place the probe in a beaker containing DI water for a few seconds.
12. GENTLY blot dry with a paper towel and place probe in the 100 ppm standard solution.
13. While stirring, monitor the value which should be changing in the upper right hand corner of the calibration box.
14. When the number is reasonably stable, uncheck the “ON” box next to reading one.
15. Enter 100 for the value.
16. Place probe back in beaker of DI water, blot dry, and place in 500 ppm standard.
17. Check the “On” box next to reading 2.
18. When reading is stable, uncheck the on box.
19. Enter 500 for the value.
20. Click Next, then Finish.
21. Now click the acquire button.
22. Once again wash probe with DI water and blot dry.
23. Place probe in first sample solution.
24. When ready, click the start button at the bottom of the screen.
25. The program will begin taking nitrate concentration measurements every 10 seconds.
26. Stir solution constantly for 5 minutes while taking readings.
27. After 5 mins has passed, click stop button.
28. Go to the Analyze screen.
29. Highlight both columns of data.
30. Copy and paste into Excel
31. Find the average of the numbers, this is the average chloride concentration for your sample.
32. Repeat steps 22-31 for all samples.
33. asd
34. In the computer workrooms, plotting bar graphs of the 7 sampling sites.