Suppose we have put some salt in water. My state of knowledge is, that a hydration envelope is formed from the oxygen side of the water molecules on the Na+-Ions and one another from the hydrogen side of the water molecules on the (Cl-)-Ions to drag these out of the crystal.

My questions now are:

  1. When the hydration envelope is formed on the ions, does it (partially) change the charge of the ions?

  2. (Now the main question) If I would put two magnets with opposite poles on both sides of the container, in which the salt solution is, would the ions be pulled to the side of the opposite pole, (if yes or no, then why)?

I made a little sketch an let the hydration envelope out for the sake of the little place.

And one another thing. There is no reason to downvote my question, because I am not playing around here, but the question just jumped in my head

pulling charged Na and Cl ions to the side of the magnet

  • $\begingroup$ I am not certain, but I think charges themselves are not affected by a magnetic field. And Na+ and Cl- both are closed shell i.e. no unpaired electrons, so they are diamagnetic. So overall your ions won't be attracted by magnets... $\endgroup$
    – S R Maiti
    Jan 2, 2021 at 23:14
  • 3
    $\begingroup$ ... because remember, charges are affected by a magnetic field only if they are moving. If your electrolytic solution flows in an orderly fashion, and you apply a magnetic field, only then you will see movement of the ions. This is called Hall effect (en.wikipedia.org/wiki/Hall_effect) $\endgroup$
    – S R Maiti
    Jan 2, 2021 at 23:19
  • $\begingroup$ Do you mean charges rather than magnets? That’s basically the principle of electrophoresis $\endgroup$
    – Andrew
    Jan 3, 2021 at 0:31

1 Answer 1


There are a couple of issues: first, a uniform magnetic field doesn't exert a force on stationary charges and secondly, when the charges are moving the force is at right angles to the magnetic field. There are a few ways to get the charges moving. You could have an electric current flow from the bottom of your figure to the top. The $\text{Na}^+$ ions would move with the current, up the page and since the magnetic field points to the left in your figure, the $\text{Na}^+$ ions would be pushed towards the reader by the right hand rule resulting in higher electric potential near the reader. This is called a positive Hall effect. The $\text{Cl}^-$ ions would move against the current, down the page and paradoxically would be pushed towards the reader again by the right hand rule, this time resulting in a lower electric potential near the reader: a negative Hall effect.

Another way is to have the electric current directed out of the page. Positive $\text{Na}^+$ ions move towards the reader and then are pushed down the page by the magnetic field according to the right hand rule. Negative $\text{Cl}^-$ ions move away from the reader and are also pushed down the page by the magnetic field via the right hand rule. This is the principle of magnetohydrodynamic propulsion.

Another way is to have the brine flowing up the page which forces $\text{Na}^+$ charges towards the reader and $\text{Cl}^-$ charges away from the reader by the right hand rule, both resulting in higher electrostatic potential on the near side of the stream. This would be magnetohydrodynamic propulsion in reverse operating as a generator.

  • 2
    $\begingroup$ +1 for a nice answer, I was about write about the Lorentz force but you already addressed it. If the velocity is zero, then the force is also zero. $\endgroup$
    – AChem
    Jan 3, 2021 at 1:44

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