pH in HF v HI

[805594676]

Hi! I had a quick question. So, if a two atoms in a molecule are more polarized, then it will form a stronger acid. For example, HCl is a stronger acid than HI. However, HF is a weaker acid then HCL, even though F is more electronegative. Can someone please explain why? Thanks!

[Rhea Desai 1A]

HF is a weak acid because the atoms are more polarized so it is harder to give off the H+ ion. This means it is harder to dissociate in water. Strong acids fully dissociate in water. I think HCl is weaker than HI because HCl is more polarized so its harder to remove the H+ ion. Iodine has a larger orbital and is less electronegative so the bond between H and I is weaker and therefore easier to break, making it a stronger acid.

[Quynhanh Nguyen 1C]

Hi! From least to greatest strength, HF < HCl < HBr < HI. This is because iodine is a much bigger molecule than fluorine and therefore has a longer bond with hydrogen. As we learned in 14A, the longer the bond, the easier it is to break, therefore making HI the strongest and most volatile acid. Hope that helps!

[AlexandriaHunt2J]

Hi! For binary acids (H-A acids) in the same period, as the A atom becomes more electronegative, the HA bond is more polarized, meaning the acid becomes stronger. For binary acids in the same group, as the A atom becomes larger and the HA bond length is longer, the acid is stronger. When comparing HF and HI, Flourine and Iodine are in the same group, so you'd use the second rule: because I is larger and the HI bond length is longer, it's easier to break, meaning this acid is stronger. This is why HI > HBr > HCl > HF.

[605733348]

When the bond is more polarized, it's harder to give off protons.

[William Huang 1K]

since F- is a smaller ion than I-, the electrons are not as delocalized and the resulting bond is stronger, meaning it takes more to dissociate H+ from it making it a weaker acid than HI.