Why do acids donate protons?

  • #1
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The concept I have not been able to grasp, is WHY an acid has to have a positive hydrogen ion, and a base has to have a negative hydroxide ion. From what I understand, when an acid is placed in an aqueous solution is the following:

H30 and Cl react to turn into H30+ and Cl-, but what I don't understand is why the H30 is positive, and the chlorine negative. And why is it that an acid dissolved into positive hydrogen ions, not negative. This process is very hard, and if I could get a link to a complete tutorial, Id be very grateful.

Edit: OH I GET IT, a Hydronium Ion is H30+, but in order for a H20 compound to become positive it gains an proton, as is common with all Acids. This proton comes from another element/compound, for example, chlorine reacts with hydrogen and gives H its proton (why not one of its valence electrons?) thus making H20+, then when another Hydrogen atom comes along, it combines with the H20+ to make H30+
 
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Answers and Replies

  • #2
137
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Not usre if I really get what you're asking about the 'why'.

Chlorine, due to its electron shell configuration, tends to accept an electron easily. Because of this trait, it is defined as a base.

Likewiese but opposite, H3O because of its electron shell config tends to want to emit an electron. Because of this trait it is defined as an acid.

This is the Arrenhius acid correct? I still don't understand why the ions dissolve in an aqueous solution, I understood that acids accept protons, making them positive ions. But why this makes them dissolve in an aqueous solution I have no idea.
 
  • #3
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Not usre if I really get what you're asking about the 'why'.

Chlorine, due to its electron shell configuration, tends to accept an electron easily. Because of this trait, it is defined as a base.

Likewiese but opposite, H3O because of its electron shell config tends to want to emit an electron. Because of this trait it is defined as an acid.

Even the term "dissolve" isn't lucid to me. What I understand it means is the Ions they release their bonds and react with the the water, acting as a base.
 
  • #4
DaveC426913
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I have deleted my reply because it was not applicable to your question. Sorry 'bout that.
 
  • #5
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I have deleted my reply because it was not applicable to your question. Sorry 'bout that.

I am thankful you are trying to help, many won't have the patience to explain. Please try to explain this, I am beginning to grasp this more due to some help outside this site.
 
  • #6
Borek
Mentor
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The concept I have not been able to grasp, is WHY an acid has to have a positive hydrogen ion, and a base has to have a negative hydroxide ion.

This is putting things on the head. Acids doesn't have to have an acidic hydrogen, it IS an acid BECAUSE it has an acidic hydrogen.

Edit: OH I GET IT, a Hydronium Ion is H30+, but in order for a H20 compound to become positive it gains an proton, as is common with all Acids. This proton comes from another element/compound, for example, chlorine reacts with hydrogen and gives H its proton (why not one of its valence electrons?) thus making H20+, then when another Hydrogen atom comes along, it combines with the H20+ to make H30+

This proton doesn't come from "another element/compound", it comes from an ACID. Why? Because we call substances that will easily donate a proton acids.

In the case of hydrochloric acid you start with molecule of HCl (for now it doesn't matter where it came from), when it dissolves, it dissociates, giving out H+ and Cl-. H+ reacts with water giving hydronium cation. In fact it is not possible to split this process into two steps, as they occur simultaneously, so you may as well say HCl reacts with water molecule producing hydronium and chloride anion.
 
  • #7
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This is putting things on the head. Acids doesn't have to have an acidic hydrogen, it IS an acid BECAUSE it has an acidic hydrogen.


when it dissolves, it dissociates, giving out H+ and Cl-
That is what I want to know, why it dissolves into a positive ion, not a negative. When i know the science behind things I am able to grasp them much easier.
 
  • #8
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This is putting things on the head. Acids doesn't have to have an acidic hydrogen, it IS an acid BECAUSE it has an acidic hydrogen.



This proton doesn't come from "another element/compound", it comes from an ACID. Why? Because we call substances that will easily donate a proton acids.

In the case of hydrochloric acid you start with molecule of HCl (for now it doesn't matter where it came from), when it dissolves, it dissociates, giving out H+ and Cl-. H+ reacts with water giving hydronium cation. In fact it is not possible to split this process into two steps, as they occur simultaneously, so you may as well say HCl reacts with water molecule producing hydronium and chloride anion.

Is this how the acid is made, or what happens when it reacts with water?
 
  • #9
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http://en.wikipedia.org/wiki/Lewis_acid#Proton_as_Lewis_acid
The proton (H+) is one of the strongest, but is also one of the most complicated Lewis acids. It is convention to ignore the fact that a proton is heavily solvated (bound to solvent). With this simplification in mind, acid-base reactions can be viewed as the formation of adducts:

* H+ + NH3 → NH4+
* H+ + OH- → H2O

http://en.wikipedia.org/wiki/Lewis_acid#Lewis_bases
Many Lewis bases are "multidentate," that is they can form several bonds to the Lewis acid. These multidentate Lewis acids are called [chelating agent]]s.

http://en.wikipedia.org/wiki/Lewis_acid#Hard_and_soft_classification
Lewis acids and bases are commonly classified according to their hardness or softness. In this context hard implies small and nonpolarizable and soft indicates larger atoms that are more polarizable.

* typical hard acids: H+, alkali metal cations, boranes, Zn2+
* typical soft acids: Ag+, Mo(0), Ni(0), Pt2+
* typical hard bases: ammonia and amines, water, carboxylates, fluoride and chloride
* typical soft bases: organophosphines, thioethers, carbon monoxide, iodide
 
  • #10
Borek
Mentor
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That is what I want to know, why it dissolves into a positive ion, not a negative. When i know the science behind things I am able to grasp them much easier.

Every substance that dissociates into ions has to dissociate into positive and negative ions, as final total charge must be identical to the initial charge.

Acid is made of two parts - proton that will dissociate as a cation, and larger part that will be negatively charged. This larger part usually contains elements of high electronegativity. That means they keep their electrons very strongly, which exposes the proton - so it can be easily removed.

I told you at least once earlier, you are trying to run before knowing how to crawl. Don't try to go into minute details before you will get general ideas right. Granpa's links (while addressing the problem) will only confuse you more.

You have opened several threads asking different question - nothing wrong with that, but so far you have never get to the end of understanding simple and basic principles, you always jump to something else. You won't get far this way.

For now you should just remember that acids dissociate to to proton and some negatively charged anion, and they have their reasons to do so.
 
  • #11
13
0
The concept I have not been able to grasp, is WHY an acid has to have a positive hydrogen ion, and a base has to have a negative hydroxide ion. From what I understand, when an acid is placed in an aqueous solution is the following:

H30 and Cl react to turn into H30+ and Cl-, but what I don't understand is why the H30 is positive, and the chlorine negative. And why is it that an acid dissolved into positive hydrogen ions, not negative. This process is very hard, and if I could get a link to a complete tutorial, Id be very grateful.

Edit: OH I GET IT, a Hydronium Ion is H30+, but in order for a H20 compound to become positive it gains an proton, as is common with all Acids. This proton comes from another element/compound, for example, chlorine reacts with hydrogen and gives H its proton (why not one of its valence electrons?) thus making H20+, then when another Hydrogen atom comes along, it combines with the H20+ to make H30+

Acids do not have to be positively charged. It is kind of relative.

H2O+ ?!!?

Chlorine gives hydrogen its proton???? I think you mean the chlorine ION (Cl-) donates e- to the hydrogen ION (H+) to form HCl.

H3O+ is positive because oxygen at a its most stable non-charged state has 2 free electron pairs. To add a proton onto there, you must give an electron over to the proton to form a bond, reducing the amount of electrons on the oxygen by 1.
 

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