Acid strength and bond length

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Aishwarya Kosgi 1F
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Acid strength and bond length

Postby Aishwarya Kosgi 1F » Wed Dec 02, 2020 7:05 pm

Hi! I was wondering what the relationship between bond length and acid strength is? In the example of HCl and HBr, since HBr's bond is longer, I was wondering which one is the stronger acid and how to tell? Thank you!

Wil Chai 3D
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Re: Acid strength and bond length

Postby Wil Chai 3D » Wed Dec 02, 2020 8:11 pm

HBr has a longer bond length because the bond between the H and Br is weaker compared to the bond between H and Cl. Thus, HBr it will more readily dissociate, meaning it will contribute more H+ ions to solution, which means HBr is stronger. Hope this makes sense!

Olivia Yang 3J
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Re: Acid strength and bond length

Postby Olivia Yang 3J » Wed Dec 02, 2020 8:52 pm

The general rule is that the shorter the bond the weaker the acid (longer bond -> stronger acid (because it readily dissociates))

Lily Kiamanesh 2G
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Re: Acid strength and bond length

Postby Lily Kiamanesh 2G » Wed Dec 02, 2020 10:15 pm

A strong acid is one that is almost completely ionized (fully dissociated), releasing many protons into solution. To determine the strength of an acid, we look to its intramolecular attraction and bond length. In the case of HF for example, it is not a strong acid because F, a very electronegative atom, will not dissociate from the H, but remain bonded to it. Also, F is a small atom, so the bond is short and strong. In contrast, HI is a strong acid because Iodine is not extremely electronegative, and its very large radius creates a long bond length that can easily be broken.

Crystal Pan 2G
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Re: Acid strength and bond length

Postby Crystal Pan 2G » Thu Dec 03, 2020 12:35 pm

The longer the bond length, the weaker the bond, which means it is more easily dissociated/ionized. In lecture, Dr. Lavelle said that strong acids are almost completely ionized/dissociate in solution, therefore the longer the bond, the stronger the acid. (In most cases)

Michael Sun Dis 3G
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Re: Acid strength and bond length

Postby Michael Sun Dis 3G » Thu Dec 03, 2020 4:11 pm

Longer bonds are weaker, which makes for stronger acids. Acid strength is determined by percent dissociation, with stronger acids dissociating more. HBr is thus a stronger acid, as it more easily dissociates in water.

Selena Quispe 2I
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Re: Acid strength and bond length

Postby Selena Quispe 2I » Thu Dec 03, 2020 4:37 pm

Hi! So the longer the bond (weaker bonds) = stronger acids. For a strong acid you want the bond to break easily so it can easily give off its proton. And in HBr the Bromine is much bigger than the chlorine in HCl therefore the bond would be longer (weaker bond) and is a much stronger acid than HCl. I hope this helps!!

Maya Johnson 2a
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Re: Acid strength and bond length

Postby Maya Johnson 2a » Thu Dec 03, 2020 5:22 pm

Bonds that are longer are more easily broken, making them present in strong acids because they dissociate well.

Hannah Rim 2D
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Re: Acid strength and bond length

Postby Hannah Rim 2D » Fri Dec 04, 2020 2:06 am

Weaker/ longer bonds are stronger acids because the molecule can dissociate more easily in water. In your example, HBr has a longer bond length than HCl. Thus, HBr is a stronger acid because it is weaker and will dissociate more in water. Hope this helps!

Libby Dillon - 1A
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Re: Acid strength and bond length

Postby Libby Dillon - 1A » Fri Dec 04, 2020 11:24 am

The first way explained in lecture to determine the strength or weakness of an acid is by looking at bond length. Larger atoms are going to have larger bonds, which are weaker and more easily broken. Longer bonds are more easily dissociated in water, which is a characteristic of a strong acid.

Joseph_Armani_3K
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Re: Acid strength and bond length

Postby Joseph_Armani_3K » Fri Dec 04, 2020 3:17 pm

HBr would be the stronger acid. The longer the bond in a binary acid, the stronger it will be. When the bond is weaker, the H+ ion is easier to remove, meaning the acid would release more H+ ions into a solution by dissociating. Hence, the acid would be stronger.

Jiapeng Han 1C
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Re: Acid strength and bond length

Postby Jiapeng Han 1C » Fri Dec 04, 2020 10:25 pm

For a structure of H-A, the longer the bond, the weaker the attraction, thus the stronger the acidity. In this case, HBr is more acidic than HCl.


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