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# Autoionization of water

Autoionization of water into hydronium and hydroxide ions.

## Want to join the conversation?

• How many times per minute does the hydrogen bond break and create again?
• The time scale is about 10¹¹ times per second.
• at 6.00 pm, why 1 litre of of h2o is 56 moles of h2o?? we know that 22.4 litre of any substance = 1 mole of that substance.
• 1 mole per 22.4L is for an ideal gas at 0 C

Water has a density of ~1g/mL so 1L is approx 1000g.
Water has a molar mass of ~18g/mol
1000g / 18g/mol = ~56 moles
• does the water molecule also split up in hydrolysis and is this essential for the reaction to take place?
• hydrolysis means splitting of water. So yes it does split and is essential to the reaction
• is there a way to make it more likely for water to auto ionize?
• Yes, if one were to add acids or water, they would ionize the water which would then propagate. For example an acid would donate a proton to a water molecule, which would shortly thereafter shake it off onto another molecule in a chain and soforth.
• So when I'm drinking water i'm not only drinking H2O molecules but also hydronium and hydroxide molecules ? Or does the concentration depend on other factors ?
• The concentration varies slightly with temperature. Your body is almost two-thirds water, so you also contain hydronium and hydroxide ions.
• How do you know what order to put the letters in?
For example, Sal wrote H3O and then OH, why not HO? It matters what order you put the letters in, right? Thanks!
• There are conventions about what order to write the letters in, but for something like hydroxyl the order really doesn't matter.

However, it is incorrect to leave off the charge — HO (or OH) is free radicle not an ion and is not what you meant!

HO⁻ and ⁻OH are used and generally acceptable, as is OH⁻. In general, keeping the charge next to the atom where most of the charge will be found is clearer, but for the really common ions like hydroxyl most people know what is meant so it doesn't really matter.

That may look like a lot of work, but you've probably watched many of the videos already under "Chemistry of life". A deep understanding of chemistry is essential to anyone interested in modern biological sciences or medicine, so I really encourage you to take the time to work though all of the chemistry material.
• During the auto-ionization of H20 does it ever happen that the Hydrogen (who left its electron behind separating from one H20 molecule),decides to go back to the same H20 molecule it just left? or does it always move to another H20 molecule to form H3O+ ?
Thanks!
• It could happen, but my feeling is that it is very unlikely. All the molecules in a liquid are constantly moving and the resulting HO¯ and H₃O⁺ probably move away from each other soon after the proton transfer.

Note that in neutral water the [HO¯]=[H₃O⁺]=10⁻⁷ M. In contrast, if you work it out the [H₂O]=55.5 M. So the ~1 in a billion H₃O⁺ that just got created is much more likely to transfer the extra proton to another H₂O rather than back to its "partner" (or any other) HO¯.
• Ok so i'm pretty confused but i have a question. So around Sal says that the proton is added to the other molecule's hydrogen or something like that but if a proton is added to another hydrogen wouldn't it become helium because if an element gains a proton or loses a proton it would become a totally different element. Sorry for the lame and confusing question but please help as i'm struggling. Thank you
• This oxygen in the water is forming a new coordinate bond with the proton, the H+, to form a new chemical species called the hydronium ion. Creating a new chemical species like this is a chemical reaction. A proton adding to another proton is indeed helium but that is a nuclear reaction called nuclear fusion which isn't what is happening here. Nuclear reactions like that require immense amount of energy which isn't present in water here. Hope this helps.
• is it correct to say that the dissociation of nacl in water is same as the hydrolysis of nacl?......also in the salt/acid/base hydrolysis process,if the water molecule is not ionized will it still be called hydrolysis?
• hydrolysis involves breaking of covalent bonds, thus NaCl is not hydrolysed. Water molecule is always hydrolysed when it is involved in hydrolyis.
• Does the concentration of the H3O+ ions increase or decrease once it reaches 1x10^-7 M?
• If you are refering to the autoionization of water, it wont.

Here is my reasoning:

Kw= 1.0*10^-14
Water is neutral, so [OH-]=[H3O+]
Kw=[OH-]*[H3O+] so Kw=([H3O+])^2 or Kw=([OH-])^2
By the following reasoning, we can conclude that [H3O+]=sqrt([Kw]) so, sqrt(1.0*10^-14)=1.0*10^-7 which is equivalent to pH=7

Assuming that the water is neutral at 25º degrees celcius, according to Le Chatteliers principle, a system will react to counter changes to its equilibrium, so as the system is already at its equilibrium, it will not react.

Be aware that when I say "the system will not react", it is theoretically not right, because chemical equilibrium is dynamic.

Sorry for the too long answer, hope this helps!