HF is a weak acid?

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HF is a weak acid?

Postby FDeCastro_1B » Wed Dec 04, 2019 1:47 pm

Why is it that HF is considered a weak acid and not a strong acid when the definition of a strong acid is that almost every molecule or ion of that acid has lost its proton and HF seems to match that definition?

Sahil Jog 1F
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Re: HF is a weak acid?

Postby Sahil Jog 1F » Wed Dec 04, 2019 1:53 pm

Since Flourine is such a small molecule, the bond between fluorine and the hydrogen is the shortest when comparing the other halogen-based acids. This would mean that it is much more difficult to break this bond and thus less H+ exist in an aqueous solution of HF.

Sears 4A
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Re: HF is a weak acid?

Postby Sears 4A » Wed Dec 04, 2019 8:05 pm

stronger bonds between atoms mean it is more difficult for that molecule to dissociate fully (which is the definition of a strong acid)

Melvin Reputana 1L
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Re: HF is a weak acid?

Postby Melvin Reputana 1L » Wed Dec 04, 2019 10:17 pm

Another way to look at this is the trend for binary acids within the same group is bond strength. A weaker(longer) bond between the anion and H allows for easier removal of H+ which means that it is a stronger acid because it can dissociate more in water. HF is a weak acid because H-F is a short, strong bond which causes it to be unable to completely dissociate in water. Following this same logic, you would find that for the halogen group, the order of acid strength is HF < HCl < HBr < HI.

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Re: HF is a weak acid?

Postby brennayoung » Thu Dec 05, 2019 12:17 am

Fluorine is too small to accommodate the negative charge. Don't think of strength of acids based on electronegativity but based on electronegativity AND size.

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Re: HF is a weak acid?

Postby RoshniVarmaDis1K » Thu Dec 05, 2019 12:56 am

Strong acids are acids that dissociate completely. HF does not do this because the HF bond is very short and very strong, so it does not come apart.

Matthew Tsai 2H
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Re: HF is a weak acid?

Postby Matthew Tsai 2H » Thu Dec 05, 2019 8:54 pm

Due to the smaller size of fluorine, the H-F bond is very strong, preventing much dissociation in water and thus preventing HF from donating a proton.

Jade Hinds 2B
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Re: HF is a weak acid?

Postby Jade Hinds 2B » Thu Dec 05, 2019 8:57 pm

if anyone has some tips/tricks on how to easily identify strong/weak acids and bases, please share!!!

Jacob Motawakel
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Re: HF is a weak acid?

Postby Jacob Motawakel » Fri Dec 06, 2019 1:50 am

HF bond is very small and strong, making it harder to dissociate in water.

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