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A common highschool chemistry example for the polarity of water is the experiment where stream of water is deflected under the influence of a charge (electric field).

Now I have come across some condradicting claims, namely this Youtube video from Veritasium (from around 1:50) and more importantly a publication by Ziaei-Moayyed et. al..[1]

These sources suggest that this phenomenon is not based on the polarity of water but charged impurity ions in the water stream. They also claim that the electric field could also only re-orient the molecules, but not deflect them as the electric field also has an opposite effect on the other side of the dipole. This has been bothering me and it is hard to find concluding evidence either way. What are your thoughts?

References:

  1. Ziaei-Moayyed, M.; Goodman, E.; Williams, P. Electrical Deflection of Polar Liquid Streams: A Misunderstood Demonstration. J. Chem. Educ. 2000, 77 (11), 1520. DOI: 10.1021/ed077p1520.
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    $\begingroup$ At first I thought there was no way this could be hard to answer, but it seems that there is actually debate about this phenomenon to an extent. I would lean towards agreeing with that journal article because I don't think it would be published without being reasonably sound. I also just found another paper which reports distortion of the surface of a nonpolar liquid using a Van de Graaf generator, which seems quite surprising. Read about that here. $\endgroup$ – jheindel Sep 6 '15 at 6:13
  • $\begingroup$ Very interesting. Seems to be caused by induced polarization of the nonpolar molecules. Vertical offsetting requires stronger attractive force to overcome gravity, cohesion and rejecting coulomb forces (?), thus the Van de Graaf generator was needed. So is the distance between dipole sides great enough to cause noticeable acceleration due to coulomb's law? $\endgroup$ – A. La Sep 7 '15 at 14:46
  • $\begingroup$ Since impurities are charge neutral in sum (so much negative charge in ions as positive), how would electric field deflect them ? $\endgroup$ – Greg Apr 6 '17 at 14:57
  • $\begingroup$ If electric field cannot deflect electric dipoles, magnetic field cannot deflect magnetic dipoles (same force laws, only letter is changed) - which is off course not true.. $\endgroup$ – Greg Apr 6 '17 at 15:01
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An electrostatic field will attract both conducting and nonconducting materials even though those materials have no initial charge through electrostatic induction. That is why you can pick up lint or aluminum foil with a charged comb or balloon. See this demo with a neutral aluminum can.

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  • $\begingroup$ Good point. The video was about inducing charge to a conductive material (aluminum) but polarization works for nonconducting materials as well. Why then the hexane stream is not deflected in this video? Is it because the attractive force is simply too weak to notice? $\endgroup$ – A. La Sep 7 '15 at 14:56
  • $\begingroup$ Exactly! Water and alcohols are polar and are, but given sufficient voltage, even non-polar hexane would exhibit some attraction due to electrostatic induction. The degree of polarity corresponds roughly to the dielectric constant: hexane=~2; isopropanol=~20; water=~80 (macro.lsu.edu/howto/solvents/Dielectric%20Constant%20.htm). BTW, thanks for listing that video! $\endgroup$ – DrMoishe Pippik Sep 7 '15 at 18:44
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G. W. Francis "Electrostatic Experiments" 1844 showed that charge separation in water can be created by electrostatic induction (experiment 153). William Thomson (Lord Kelvin) later demonstrated that charge separation in water occurs even in the usual electric fields at the earth's surface and developed a continuous electric field measuring device using that knowledge. He then developed the water-dropper electrostatic high-voltage generator using the same concept. Others have since shown experimentally that the amount of charge separation in water is proportional to the electric field strength. I believe that a stream of water is deflected because the electric field induces macroscopic charge separation in the water and not because water has polarisable molecules that have reoriented.

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