Why isn't HF a strong acid?

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dana hu 1B
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Why isn't HF a strong acid?

Postby dana hu 1B » Sat Dec 12, 2020 3:41 pm

Hello, I am confused why HF is not a strong acid. Isn't electronegativities between the two ions great, like HCl, and it is polar?
thank you!

Crystal Hsueh 2L
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Re: Why isn't HF a strong acid?

Postby Crystal Hsueh 2L » Sat Dec 12, 2020 3:45 pm

I believe HF is a weak acid because of how strong the bond is between H and F. It is such a strong, short bond that it will not completely dissociate, and strong acids are characterized by being able to completely dissociate.

Chanel Mao 3D
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Re: Why isn't HF a strong acid?

Postby Chanel Mao 3D » Sat Dec 12, 2020 3:46 pm

Hi!
When looking at HF, we have to take into account the bond length between the two atoms. Since the bond between H and F is relatively short, it will be harder for the bond to break when placed into a solution. Because of this, the ions will not dissociate as easily, which is why HF is not considered a strong acid.

Catie Donohue 2K
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Re: Why isn't HF a strong acid?

Postby Catie Donohue 2K » Sat Dec 12, 2020 3:47 pm

I agree with the previous response - because the bond between H and F is so strong due to their electronegativity difference, the molecule will not be inclined to lose the H atom (the easier an acid gives off H, the stronger it is).

Zaid Bustami 1B
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Re: Why isn't HF a strong acid?

Postby Zaid Bustami 1B » Sat Dec 12, 2020 3:53 pm

Hi Dana!
HF is not a strong acid because fluorine is a very small atom. Although the electronegativity difference in this molecule is larger than for HBr and HI, which are strong acids, the small length of the bond makes for a very strong H-F bond. The short length of the bond overcomes any extra weakness that the high polarity of the bond brings.
Another way to think about this is to look at the stability of the anion, F-. The fluoride ion is EXTREMELY unstable and will at any cost try to form a bond with an electron-deficient species like a proton (it is an extremely strong lewis base). F- is highly corrosive because of this and so HF, even though it's a weak acid, is pretty dangerous because of the fluoride ions it produces when dissolved in water. Because of its instability, it is way more favorable for F- to bind to H+ and form HF, so HF will tend to only partially dissociate in water.

Brandon Le 3C
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Re: Why isn't HF a strong acid?

Postby Brandon Le 3C » Sat Dec 12, 2020 4:05 pm

HF is not a strong acid due to its smaller atomic radius. This lower radius (in comparison to the increasing size of Cl, Br, and I) results in a lower distance between the H and F atoms, therefore making the bond significantly stronger. When the bond is stronger, it becomes more difficult for the bond to sever and produce more H+ (or H3O+) in the water. Therefore, we cannot assume that HF completely dissociates, and so it cannot be a strong acid.

Mauricio Maravilla 3C
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Re: Why isn't HF a strong acid?

Postby Mauricio Maravilla 3C » Sat Dec 12, 2020 4:06 pm

HF doesn't completely dissociate cause of how intensely the fluorine bonds to the hydrogen. As a result, the solution that it is supposed to be dissolved in is not acidic, or best case weakly acidic.

Jason_John_2F
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Re: Why isn't HF a strong acid?

Postby Jason_John_2F » Sat Dec 12, 2020 4:14 pm

hf is a weak acid due to its size the bond length is short and therefore stronger making it dissociate less in water

LovepreetSran_3H
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Re: Why isn't HF a strong acid?

Postby LovepreetSran_3H » Sat Dec 12, 2020 4:22 pm

HF is a weak acid because the bond between H and F is extremely short since F has a very small atomic radius. The shorter a bond is, the stronger the bond is. The stronger bond makes it harder for the HF bond to break when dissolved in H2O causing the acid to be weak.

Crystal Pan 2G
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Re: Why isn't HF a strong acid?

Postby Crystal Pan 2G » Sat Dec 12, 2020 4:28 pm

F is very electronegative, so the bond between H and F are stronger than with the other H-halogen acids, which means its a weaker acid!

Eric Cruz 2G
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Re: Why isn't HF a strong acid?

Postby Eric Cruz 2G » Sat Dec 12, 2020 4:47 pm

HF is not a strong acid because F has a high electron affinity and is very electronegative. Therefore, it is a strong bond that requires a lot of energy to break. Therefore, it is not as easy for the H+ to deprotonate and join H2o to make hydronium.

Sheryl Ocampo 1D
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Re: Why isn't HF a strong acid?

Postby Sheryl Ocampo 1D » Sat Dec 12, 2020 5:26 pm

My TA mentioned this in discussion the other day. Based on the concepts we learned, it should be a strong acid. However, it is an exception because flourine is such a small atom. The bond between hydrogen and flourine is so small and strong that it makes HF a weak acid

Anthony_Sandoval_1D
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Re: Why isn't HF a strong acid?

Postby Anthony_Sandoval_1D » Tue Dec 15, 2020 5:47 pm

HF is not a strong acid due to the high electronegativity of F and because of its extremely small atomic radius. The small atomic radius of F means it has a very short and consequently strong bond making it very difficult to break when dissolved in water.

Reese_Gover2K
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Re: Why isn't HF a strong acid?

Postby Reese_Gover2K » Wed Dec 16, 2020 3:21 pm

It's because since F is such a small atom the bond length would be much smaller between H and F than between H and Cl so since HF has just a small enough bond length it would not be an acid.

reyvalui_3g
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Re: Why isn't HF a strong acid?

Postby reyvalui_3g » Wed Dec 16, 2020 4:10 pm

It is because the F is so electronegative that in solution it will not give up its hydrogen very easily.

Joshua Swift
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Re: Why isn't HF a strong acid?

Postby Joshua Swift » Wed Dec 16, 2020 6:30 pm

Fluorine's atomic radius is not very large meaning the molecule's bond is stronger compared to HCl, HBr, or HI. The bigger the atom, the weaker the bond and the stronger the acid.

Isabel_Eslabon_2G
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Re: Why isn't HF a strong acid?

Postby Isabel_Eslabon_2G » Wed Dec 16, 2020 6:34 pm

F is very electronegative, so it does not want to dissociate with the H atom. This is why it is not a strong acid.

Among HCl, HBr, and HI, HI is the strongest acid because it gives up protons the easiest. The bond for HI is the longest, so it is the weakest.

Carolina Gomez 2G
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Re: Why isn't HF a strong acid?

Postby Carolina Gomez 2G » Wed Dec 16, 2020 11:14 pm

HF is a weak acid because the bond between the two is a strong bond which makes the atoms hard to dissociate.

CesarLec1
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Re: Why isn't HF a strong acid?

Postby CesarLec1 » Thu Dec 17, 2020 1:21 am

It is not a strong acid because the bond between H and F is relatively strong so the bond does not break easily because the F ionic radii is relatively small thus since the bonds do not break easily, it is considered a weak acid.

Talia Dini - 3I
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Re: Why isn't HF a strong acid?

Postby Talia Dini - 3I » Thu Dec 17, 2020 1:47 am

Hi! HF is a weak acid because the bond length between H and F is short. Thus, when placed in a solution, it will be hard for the bond to break and for the ions to easily dissociate.

Griffin G
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Re: Why isn't HF a strong acid?

Postby Griffin G » Thu Dec 17, 2020 1:48 am

HF isn't a strong acid because F bonds so tightly to H, that it is hard to get the two to separate. It's still a super dangerous compound though.

IshanModiDis2L
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Re: Why isn't HF a strong acid?

Postby IshanModiDis2L » Thu Dec 17, 2020 1:51 am

HF is not a strong acid because the bond between H and F is too strong. Essentially the bond length between H and F is relatively short, making it harder for the bond to break when placed into a solution. This makes the dissociation harder and overall lowers the Ka.

Adam_ElSayed_3B
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Re: Why isn't HF a strong acid?

Postby Adam_ElSayed_3B » Thu Dec 17, 2020 2:24 am

HF doesn't want to disassociate. The electronegativity is different enough that they're basically stuck to one another, and won't act as a strong acid.

Sejal Parsi 3K
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Re: Why isn't HF a strong acid?

Postby Sejal Parsi 3K » Thu Dec 17, 2020 7:56 am

It’s because fluorine is so electronegative that in a solution, it won’t give up its hydrogen easily, and strong acids tend to dissociate easier in solutions.


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