I'm conducting some pH measurements with solutions containing NaOH and I'm a bit concerned that carbon dioxide will dissolve and affect my measurements by lowering the pH according to the reaction: $$\ce{2 OH- + H2CO3 -> 2 H2O + CO3^2-}$$ This would consume my $\ce{OH-}$ ions; I obviously don't want that kind of interference.

Are the kinetics such that I should cover my setup, or can I ignore it's effect on a, say ~1 h timescale? Or ~24 h?

Some additional information, after request:

  • I don't have many cations that would form insoluble compounds with carbonate
  • I work at room temperature
  • The setup is a beaker (diameter 10cm-ish) with approximately 200ml volume
  • The reaction is supposed to be between sand and NaOH (tiny particles are not inert)

  • $\endgroup$
    • 1
      $\begingroup$ Could you include a bit more details, like the volumes you're working with, how you measure pH, what you are actually doing during the measurements, anything that could somehow influence the reaction... For what it's worth, I don't think the effect is very large in this time frame, especially when you have a small surface exposed. $\endgroup$ – Martin - マーチン Jul 21 '17 at 11:20
    • 1
      $\begingroup$ I guess this paper can help you ! $\endgroup$ – ParaH2 Jul 21 '17 at 21:02
    • $\begingroup$ Since even modern air is ~400 ppm (0.004 %), then consider how much is in the air-space in the beaker. If it's enough to affect your experiment, then cover the beaker or put a non-reactive oil layer on the solution. $\endgroup$ – DrMoishe Pippik Jul 23 '17 at 22:51

    Your Answer

    By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

    Browse other questions tagged or ask your own question.