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Author Topic: How HCl and NaOH dissolves in water  (Read 1008 times)

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ZekR

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How HCl and NaOH dissolves in water
« on: January 24, 2013, 05:08:29 PM »

Hello,

I am a novice at chemistry and I am trying to understand in some detail what happens when HCl dissolves in water as well as what happens when NaOH dissolves in water, so I tried to diagram it out (see attachment).  But I have a couple of questions (in red font in diagram). 

For example, when plain Cl gas dissolves in water, each Cl- ion gets surrounded by H2O (ion-dipole bonds), but does the same thing happen when HCl dissolves: does each Cl- ion get surrounded by H3O ions (ionic bonds)?  I would assume that each Cl- ion would strive to hook up with something else after losing its H pal....

And when NaOH dissolves, same question (=what happens with the Na+ ion)?

Also, if there are other inaccuracies in my diagram, please let me know.

Thanks.
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Hunter2

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Re: How HCl and NaOH dissolves in water
« Reply #1 on: January 24, 2013, 06:55:14 PM »

Plain chlorine reacts with water:

Cl2 + H2O => HCl + HClO

Cl- and also ClO- will be surounded by water molecules.
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ZekR

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Re: How HCl and NaOH dissolves in water
« Reply #2 on: January 24, 2013, 07:49:52 PM »

Thanks, but that was not quite what I was asking.
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Borek

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Re: How HCl and NaOH dissolves in water
« Reply #3 on: January 24, 2013, 09:23:54 PM »

For example, when plain Cl gas dissolves in water, each Cl- ion gets surrounded by H2O (ion-dipole bonds)

When plain Cl2 dissolves in water amount of Cl- produced is very low. Are you sure you are not confusing something?

Quote
but does the same thing happen when HCl dissolves: does each Cl- ion get surrounded by H3O ions (ionic bonds)?  I would assume that each Cl- ion would strive to hook up with something else after losing its H pal....

All ions in the solution always do arrange water molecules around them. Both anions and cations do it, Cl- is not different. However, the effect is more prominent in the case of smaller ions, as they have more concentrated charge - you can think about it in terms of distance between the charged ion and water dipole. The smaller the distance, the stronger the attraction.

This effect is called solvation.
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ZekR

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Re: How HCl and NaOH dissolves in water
« Reply #4 on: January 25, 2013, 06:03:37 AM »

When plain Cl2 dissolves in water amount of Cl- produced is very low. Are you sure you are not confusing something?
I am pretty sure I am confusing something...

All ions in the solution always do arrange water molecules around them. Both anions and cations do it, Cl- is not different. However, the effect is more prominent in the case of smaller ions, as they have more concentrated charge - you can think about it in terms of distance between the charged ion and water dipole. The smaller the distance, the stronger the attraction.
So in the case of HCl + H2O (fully solvated), which results in CL- + H3O, does each Cl- get surrounded by whatever H2O molecules that are left (=those that did not form H3O+ with the hydrogens from HCl), and are there no bonds between Cl- and H3O+ at all?  Does the H3O+ molecules, which are also ionic, also get surrounded by H2O with ion-dipole bonds?
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ZekR

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Re: How HCl and NaOH dissolves in water
« Reply #5 on: January 25, 2013, 08:38:05 PM »

I did some more research on this and here is an attempt to answer my own question.   

When HCl gets solvated, each chlorine ion forms ion-dipole bonds with up to 6 water molecules and each hydronium ion forms hydrogen bonds with an average of 6 water molecules.

When NaOH gets solvated, each sodium ion forms ion-dipole bonds with up to 6 water molecules and each hydroxide ion forms ion-dipole bonds with 4 or 5 water molecules.

I have attached an updated diagram.

I want to make sure I get this, so if I have something wrong, please tell me.

Thanks.
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Borek

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Re: How HCl and NaOH dissolves in water
« Reply #6 on: January 26, 2013, 12:49:59 AM »

I don't see anything wrong.

Ions in the solution can also create pairs - this is not equivalent to bonding, but these pair are relatively stable (and effect of their creation can be relatively easy to measure). You can think about these pairs as of a structure of a higher level than the one produced by solvation (which is a structure level up from typical bonding).
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Arkcon

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Re: How HCl and NaOH dissolves in water
« Reply #7 on: January 26, 2013, 03:14:04 AM »

I did some more research on this and here is an attempt to answer my own question.   

When HCl gets solvated, each chlorine ion forms ion-dipole bonds with up to 6 water molecules and each hydronium ion forms hydrogen bonds with an average of 6 water molecules.

When NaOH gets solvated, each sodium ion forms ion-dipole bonds with up to 6 water molecules and each hydroxide ion forms ion-dipole bonds with 4 or 5 water molecules.

This is what I'd heard, but I have no citation, nor do I know how exactly scientists determine what happens.  But yes, solvation of charged atoms and molecules occurs by clusters of water molecules, and those cluster also interact with more distant water molecules, changing the properties of a large group of water molecules.  This dynamic relationship is responsible for the various properties of water solution of charges moieties.  Its hard to look up these "cluster" of water molecules with changed properties, because if I try online, I eventually end up sent to pseudoscience regarding water clusters.
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curiouscat

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Re: How HCl and NaOH dissolves in water
« Reply #8 on: January 26, 2013, 03:16:31 AM »


This is what I'd heard, but I have no citation, nor do I know how exactly scientists determine what happens. 

One way is simulations.
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ZekR

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Re: How HCl and NaOH dissolves in water
« Reply #9 on: January 26, 2013, 05:34:18 AM »

Great.  Thanks for your input!
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