Why does HCl dissolve? (1 Viewer)

[eleco]

Why does HCl dissolve in water if Cl is a more electro negative element that O?

 

[Casmira]

Doesn't Cl become a negative ion and float between The hydrogen end of water?

 

[nick1048]

like disolves like...

 

[eleco]

Doesn't Cl become a negative ion and float between The hydrogen end of water?

But how does oxygen rip the H+ ion or proton of Cl if its a less electronegative element

 

[xiao1985]

dissolve as in a physical phenomenon, where intermolecular forces are overcome or the fact that HCl ionises and hence becoming H + and Cl -?!?! if tis the latter then water does too to a small extent...

 

[eleco]

dissolve as in a physical phenomenon, where intermolecular forces are overcome or the fact that HCl ionises and hence becoming H + and Cl -?!?! if tis the latter then water does too to a small extent...

explain, why is it ionised if oxygen is less electro negative, why wouldnt Cl have a stronger attraction to its proton (H+ ion)

 

[t-i-m-m-y]

explain, why is it ionised if oxygen is less electro negative

I was under the impression oxygen is the second most electronegative element, besides flourine.. which would make sense

the oxygen is feelin' real EN, so its greedy and attracts the H+.. thus 'pulling' apart the HCl, leaving H+ and Cl-

 

[april____]

HCl

Doesn't HCl just dissolve in water to make it a less concentrated acid.
I don't really think that you need to understand why it happens... just that it does.
Remember water is polar.

 

[xiao1985]

ok if HCl is an ionic lattice for a start, then the dissolution of it not only depend on pullin strength, also the enthalpy of of the solid...

and remember, whilst it is experiencing attracting from the negatively charged Cl -, it also experience repulsion from other H + ions in the lattice...

in addition, at most only 3 Cl - ions can be adjacent to an H + ion on the corner of the lattice, where as it is possible for more than 3 oxygen atoms to exert a force on hydrogen ion...

 

[~*HSC 4 life*~]

this covers a bit of preliminary chem...firstly, HCl is a covalent molecular compound, because H and Cl have different electronegativities, a unequal sharing of electron pairs results. Cl is more lectronegative than H .: has a better ability to attract the shared pair of electrons towards itself, causing one end of the molecule to become slightly negative, and the other hydrogen end slightly positive- now, this is known as a polar covalent bond. As we know, water is also a polar molecule (due to oxygen having abetter ability to draw electrons towards itself making a partial negative charge aroudn the oxygen and a partial pos charge around hydrogen thus causing the molecule to become "bent") Because of the polar nature of water, we can understand why it is 'the universal solvent' in the sense that it can dissolve other things due to interactions between charges (including things like dipoles and ions) So when Hcl and water are mixed, the dipoles of each molecule orientate themself so that pos and neg charges are aligned causing the solution to have a somewhat constant composition.

 

[Casmira]

See the first two terms of chemistry i never really paid much attention too because i was working 6 days a week, I should go over it again, I don't even remember what electronegativity easy@#$

 

[Casmira]

this is an excellent question, to which the answer lies in any first year chemistry textbook, for those that want to look it up.

Remember, chlorine DOES have a higher EN value than oxygen, and HCl does NOT exist as an ionic lattic, this type of structual bonding only exist in solids, so far i havent encountered HCl(s), HCl in its 'natural' state is a gas and dissolved in water, acts like an acid.

Keep at this one, i'll post answer eventually


Best of Luck

my teacher was telling me that, because dissolving HCl in water free's Hydrogen ions, and as we all know solution with H+ ions is likely to be an acid

 

[~*HSC 4 life*~]

See the first two terms of chemistry i never really paid much attention too because i was working 6 days a week, I should go over it again, I don't even remember what electronegativity easy@#$

electronegativity in simple terms is how badly something wants electrons eg Cl having 7 electrons in its valence shell has a strong electronegativity (really wants that one electron to complete its shell). Don't worry if you forget some year 11 work, i sure did, but i strongly suggest you go back and continually revise the basics, because they are basics afterall and they are the foundation upon which you build your knowledge from the hsc course

 

[nit]

The oxygen atom has a higher EN than the chlorine atom (3.5 on the Pauling scale vs 3.0 for the chlorine atom). Firstly, this should be obvious, given that the chlorine atom is never part of any hydrogen bonding network (EN not high enough), and this relationship between O's EN anf Cl's EN can be rationalised by keeping in mind that chlorine occurs in the 2nd period of the periodic table, while oxygen is in the 1st and subsequently oxygen has a much smaller atomic radius and a greater effective nuclear charge Z.

 

[t-i-m-m-y]

The oxygen atom has a higher EN than the chlorine atom (3.5 on the Pauling scale vs 3.0 for the chlorine atom).

That's what I thought.. but chemcoach says Cl > O (in terms of EN)

 

[Casmira]

electronegativity in simple terms is how badly something wants electrons eg Cl having 7 electrons in its valence shell has a strong electronegativity (really wants that one electron to complete its shell). Don't worry if you forget some year 11 work, i sure did, but i strongly suggest you go back and continually revise the basics, because they are basics afterall and they are the foundation upon which you build your knowledge from the hsc course

so Fluorine would have the highest EN

from what I remember it increases as you go up ..?

 

[Xayma]

Fluorine has the highest. It decreases as atomic radius gets larger.

In fact flurorine is high enough that when it is heated has been known to strip electrons from Noble Gases.

 

[funking_you]

Answer to Question

Chem Students,

I'm terribly sorry about the other post, it was not accurate in some respects.

• HCl is a covalent compounds, however it is unque in its ability to dissolve in water. So you all know when HCl dissolves in water, it dissociates into its ions. (this is not typical of covalent compounds in general).

• In aqueous solutions these types of compounds are all acids.
  The molecules of these substances contain polar covalent bonds to hydrogen, such that the atom bonded to H pulls more strongly on the shared electron pair (due to Cl having high EN than H).
  The Cl end of the HCl molecule is partially negative, and the H end is partially positive.

• When HCl dissolved in water, the partially charged poles of H₂O molceules are attracted to the oppositely charges poles of HCl. The HCl-bond breaks, with the H becoming the solvated cation H⁺(aq) and the Cl becoming the solvated anion Cl^-(aq).

This part most people have figured out, but here is where it gets interesting.

• The solvated hydrogen cation, H⁺(aq), is a particularly strange species.
  Because the H⁺ ion is just a single proton, its positive charge is concentrated in an extremely tiny volume. Therefore, it attracts the negative pole of surrounding water molecules very strongly and becomes very tightly assosiated with them, forming a covalent bond with one of them

(NOT because oxygen has a very high EN value, but because of the way the electrons are arranged in an oxygen atoms, draw the lewis dot structure and you'll see there are is a pair of NON-bonding electrons...this covalent bond is actually a special type of bonding called a COORDINATE covalent bond...you'll learn about this in module three, i.e ozone)

• This is often indicated by writing the aqueous H⁺ ion as H₃O⁺ (hydronium ion).

I hope that all makes sense, i know it was a lot to read.


Cheers,
George

..

 

[nit]

theChemcoach, the hydronium ion is H3O+. It doesn't really matter whether you use the H+ or H3O+ notation, though in general H3O+ is better and more accurate. Also, dissolution is always the conversion of a substance from it's state at STP (or whatever it's initial conditions, generally the former), to the aqueous state. Here, dissolution is represented by the eqn HCl (g) -> HCl(aq), and this simply means that the dipole-dipole forces amongst HCl and the hydrogen bonding network in water are of similar strength and dipole-dipole forces can be formed between solute and solvent. This is distinct from the deprotonation step, which is (in terms of Lowry-Bronsted acids/bases): HCl(aq) + H2O(l) --> H3O+(aq) + Cl- (aq). This reaction only happens to occur because it is favourable (Ka large) due to thermodynamic and kinetic considerations.
As for electronegativity, it can basically be conceived of as the ability of an atom to attract electrons in a bond towards itself. In other words, it arises mainly from the electrostatic interaction between the positively-charged, shielded nucleus of an atom and the outermost electrons of the adjacent atom in the bond. i.e. the greater the number of protons in the nucleus for comparable atomic radii, the EN will be larger, or for comparable numbers of protons in the nuclei, the EN will depend on the atomic radius and number of electrons shielding the nucleus from other atoms. In our cases (O, F, Cl), the oxygen and fluorine atoms have similar radii, and the fluorine atom has 1 more proton, which outweighs the effect of the added, shielding valence electron, and so F's EN will tend to be greater than that of oxygen (4.0 vs 3.5). In comparing the oxygen atom with chlorine, the fact that the oxygen atom is so tightly bound vs the chlorine atom's 2 electron shells outweighs the fact that chlorine has more nucleons, and protons, in its nucleus, as it will have a greater number of shielding electrons in addition.

 

[~*HSC 4 life*~]

so Fluorine would have the highest EN

from what I remember it increases as you go up ..?

Yes, fluorine is the highest, it goes F, O, N, Cl...etc

whenever you get stuck, just logically look at periodic trends, as you go across a period the number of protons/electrons increases (increasing atomic number), but because the number of orbital shells remain the same (same periodic group) the nucleus (with increasing protons and electrons) can therefore can have a stronger pull on the elctrons towards itself, make its atomic radii smaller, making the ability to attract negative electrons to the positive protons in its nucleus higher, due to less distance/radii

therefore, electronegativity INCREASES as u go accross a period

when you go down a group, all that is happening is the addition of another electron orbital "shell", creating a greater distance between the nucleus and the valence elctrons (atomic radii) and as xayma said, electronegativity is in proportion to atomic radii so we can easily remember that as we go down a period, electronegativity DECREASES.