Knight:pH meter/Measurement

Overview

Basic instructions on measuring pH.

Materials

• HCl (1M and 12.1M)
• NaOH (0.1M and 5M)
• Glass pasteur pipettes and bulb
• Stir plate
• Stir bar
• 1 beaker to collect washes
• Squirt bottle with distilled water
• Kimwipes

Procedure

1. Calibrate the pH meter
2. Verify that you have exited calibration mode. It should say READ in the top left hand corner of the screen and it should NOT say CALIBRATION in the top right hand corner of the screen. To exit calibration press either the CAL or EXIT button.
3. Rinse with distilled water from a squirt bottle over a beaker used to collect washes.
   • Do not rinse the electrode into the soak beaker.
4. Touch electrode gently with Kimwipe to remove excess fluid.
5. Put solution to be pH-ed on stir plate.
6. Add stir bar.
7. Turn on stir plate to low setting.
8. Immerse electrode in solution.
   • Be sure that the stir bar won't hit the electrode tip.
9. Press the READ key.
10. Wait until the Auto-Eye stops flashing.
11. Use a glass pasteur pipette and bulb to add single drops of acid or base.
    • Add NaOH if the pH reading is too low and HCl if the pH reading is too high. If the reading is more than 1 pH unit off, use concentrated HCl (12.1 M) or NaOH (5 or 10 M). Otherwise use 1 M HCl or 0.1 M NaOH. (HCl and NaOH are the most common acids and bases to adjust pH. You can or may need to use others for your solution).
12. Press the READ key.
13. Wait until the Auto-Eye stops flashing.
14. Continue adding drops and reading the pH until the solution reaches the desired pH.
15. Rinse with distilled water from a squirt bottle over a beaker used to collect washes.
16. Touch electrode gently with Kimwipe to remove excess fluid.
17. Return the electrode to the storage solution.

Notes

• The electrodes of pH meters are both fragile and expensive. Be careful when immersing it to not hit it against the beaker or to let the stir bar hit it.

References

1. Beck Φ 300 Series operating manual http://www.beckmancoulter.com/Literature/BioResearch/511291AA.pdf

2. ISBN:0879697083

Contact

• Reshma Shetty