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Q & A: deionized water polarity

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Most recent answer: 10/22/2007
What is the polarity of deionized water?
- Sara
I guess by polarity you mean net electrical charge. Most objects have very little net charge, because whatever charge they may happen to have pulls in opposite charges which neutralize them. If water is in a container, the container surface can have a little charge which balances the charge of the water.  Even if you start with deionized water, it can pick up a few ions from a container. What the sign is of the charge depends on whether that particular surface mainly gives off positive or negative ions. 

In sum, deionized water can have either positive or negative polarity but in either case it's very small.

Mike W.


(published on 10/22/2007)

Follow-Up #1: semantics

I have no questions, but I question the answer given on polarity. Regarding polarity. Water is by nature a polar molecule with the 2 hydrogens making about a 105 degree angle to the bonded oxygen. Therefore the most dense water is at 4 C when the molecules nestle up against each other (hydrogen side moves up against the oxygen side of the next molecule) and the vibration is lowest. Going colder causes the molecules to position for crystallization which is less dense (ice floats), going warmer introduces more vibration and less order in the liquid and its density decreases (warm water rises).

Polarity has nothing to do with net charge. The net charge of a glass of water is zero since each molecule has a net charge of zero. However, the molecules are NOT symmetric and they have positive and negative sides and are polar as a result. Polarity means they the molecules will act as described above and also they will interact with photons (light) at specific frequencies. Water in the vapor phase (that is a transparent gas) is very active in the infra red.

Hope this helps.
Dan PhD physics, MS meteorology, BS Chemisty
- Dan
Denver, Colorado USA
Your description of various properties of water is correct. However, the question we were trying to answer was not ’is water a polar molecule’ but ’what is the polarity of deionized water?’ I still think we made the best guess about what was being asked, and gave a correct answer.
 Mike W.

(published on 10/22/2007)

Follow-up on this answer.