Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: smart on 18/07/2018 18:50:14
-
Hi,
Can anyone please help me to understand what is the difference between cationic and anionic water?
Thank you!
tk
-
Water is neither cationic, nor anionic so the question makes no sense.
-
As Bored chemist says, water is neutral, and therefore any charged species cannot be water.
However, I will also add that there are two primary ways that water can be ionized to form either positively charged ions (cations) or negatively charged ions (anions):
• Gain or loss of a proton (acid/base chemistry):
Water can be deprotonated to form the hydroxide anion:
H2O —> OH– + H+
Water can also be protonated to form the hydronium cation:
H2O + H+ —> H2O+
Pure water can autoionize to a very small extent (depending on the temperature):
2 H2O —> OH– + H2O+
...but hydroxide is a strong base, and hydronium is a strong acid, so they will react with each other limiting the overall concentration of each species (the product of their concentrations is about 10–14 M2)
• Gain or loss of an electron (redox)
These are less common, and the products are unstable transient species under conditions typically found on the Earth, although I believe that ionized water has been found in space.
H2O —> H2O+ + e–
or
H2O + e– —> H2O–
...Is any of this along the lines of what you are asking for tkadm30?
-
What is the difference between cationic and anionic water?
If you add salt (NaCl) to water, it dissolves to form a solution of Na+ and Cl- ions.
If you put some electrodes in the water, and apply a DC voltage, the Na+ will migrate towards the negative electrode, traditionally called the "cathode". This makes Na+ a cation.
SImilarly, Cl- will migrate towards the positive electrode, traditionally called the "anode". This makes Cl- an anion.
So salty water is simultaneously cationic and anionic water.
See: https://en.wikipedia.org/wiki/Ion#Anions_and_cations
https://en.wikipedia.org/wiki/Cathode
Footnote: In the case of rechargeable batteries, the anode and cathode can change polarity depending on whether the battery is charging or discharging...
-
So salty water is simultaneously cationic and anionic water.
Thanks a lot, @evan_au! :)
tk
-
So salty water is simultaneously cationic and anionic water.
No, the water is still not ionic.
-
salty water is simultaneously cationic and anionic water
No, the water is still not ionic.
I am puzzled by this response.
Can you please elaborate about why salty water doesn't contain cations & anions?
-
salty water is simultaneously cationic and anionic water
No, the water is still not ionic.
I am puzzled by this response.
Can you please elaborate about why salty water doesn't contain cations & anions?
I share this puzzlement. Even pure water (certainly as pure as can practically be obtained) experiences a few instances of molecules losing a proton (thereby creating a negative hydroxide ion) that immediately attaches to another water molecule, creating a positive H3O+ ion. The reaction is reversible and there is a constant generation and revconversion of ions, though the proportion present at any time is very small.
I am presuming that bored chemist's statement is a technical one in which for water to be considered ionic the bulk of the water would have to be in ionic form (as is the case, for example, with a sodium chloride crystal) and not only a small amount of it. Thus water could contain anions and cation and still, technically, be non-ionic. I'd like confirmation or clarification, though.
-
I believe that bored chemist's meaning is that the water itself is not ionic. By definition, water is H2O, a neutral compound. Solutions that are primarily water, but also contain dissolved ions, are not water, they are aqueous solutions of salts (ie the bulk properties, like density, viscosity, index of refraction, composition, conductivity, vapor pressure etc. of a 2% salt/water solution are quite distinct from the properties of pure water, and will also differ from the properties of aqueous solutions of different concentrations, or containing different solutes). On the molecular level, saltwater is essentially just a mixture of neutral water molecules and charged ions (there is some interaction between the two, so the water molecules in salt water are slightly different from water molecules in pure water, but still not anything that could really be considered ionic water.)
So based on bulk properties, saltwater is not the same as water, and shouldn't be referred to as water (from a chemists, biologists or engineers perspective--a cartographer may beg to differ), and on a molecular level, water molecules remain neutral no matter what is dissolved therein. Thus, either on a bulk or molecular level saltwater cannot be considered ionic water.
-
Anions and cations are, by definition, charged particles.
The words anionic and cationic are defined analogously.
Water isn't charged.
Water isn't anionic or cationic.
What part of that is difficult?
I'm drinking blackcurrant juice as I write this.
It's in a green plastic tumbler.
Putting red juice in a green cup does not make the cup red.
Putting sodium ions into water does not make the water cationic.
-
Anions and cations are, by definition, charged particles.
The words anionic and cationic are defined analogously.
Water isn't charged.
Water isn't anionic or cationic.
What part of that is difficult?
I'm drinking blackcurrant juice as I write this.
It's in a green plastic tumbler.
Putting red juice in a green cup does not make the cup red.
Putting sodium ions into water does not make the water cationic.
The difficult part is that water, even pure water contains ions. I have no trouble envisaging a development of terminology in which it therefore became appropriate to describe water as ionic. I understand that such a development did not occur. I would like to have clarity as to usage. I was hoping for such a clarification, rather than a repetition of your earlier statements. I floated such a clarification, expecting you to either agree with it, or explain what was wrong with it. I'm still hopeful that you will do so.
-
Water does ionize, but the ions generated are not water (H3O+ is hydronium, and OH– is hydroxide).
-
The difficult part is that water, even pure water contains ions. I have no trouble envisaging a development of terminology in which it therefore became appropriate to describe water as ionic.
Water isn't charged.
Water isn't anionic or cationic.
-
Water isn't charged.
Water isn't anionic or cationic.
I believe salt water is both positively and negatively charged. This is why salt water is heavier than tap water: https://sciencing.com/salt-water-heavier-tap-water-8735703.html
tk
-
I believe salt water is both positively and negatively charged. This is why salt water is heavier than tap water: https://sciencing.com/salt-water-heavier-tap-water-8735703.html
tk
No, it is because the metals in salt are heavier than the lighter hydrogen/oxygen of pure water.
-
Water does ionize, but the ions generated are not water (H3O+ is hydronium, and OH– is hydroxide).
Thank you for that. (It is much more helpful than Bored Chemist's repetition of the same assertions that I have twice asked to be clarified.) I am still somewhat confused. When I studied chemistry my recollection is that unionised water, hydroxide ions and hydronium ions would have been collectively referred to as water. Which of the following statements explains this:
1. I had poor teachers.
2. My recollection is faulty.
3. Usage differs in different countries
4. Usage has changed since the 1960s.
5. Other (please specify.)
Thanks in advance.
-
I believe salt water is both positively and negatively charged.
Reality trumps your "belief".
I genuinely can not see how I can clarify the assertion that water has no charge.
It just hasn't.
The hydroxide ion and hydronium ions - formed by the dissociation of water have charge, but they are not water.
Neither OH- nor H3O+ is H2O
And, as I said, I can't see how that's hard to understand.
Since it has no charge it can not be anionic or cationic.