Which one is a stronger acid- HOCl or HOI?

[zorro]

I know that HI is a stronger acid that HCl because of the weak H-I bond which can break easily in aqueous solution. But I can't understand why HOCl is a stronger acid that HOI (as per my book)?

 

[pzona]

Check their structures (hint: H isn't bonded directly to the halogen in either case). How do you think Cl will affect the H-O bond in comparison with I? Think about electronegativities here...

 

[zorro]

I got it. Chlorine being more electronegative atom withdraws oxygen towards itself, facilitating the release of H+
Thanks.

 

[Borek]

withdraws oxygen

Attracts electrons.

 

[LudusRex]

The strength of an acid is determined by its ability to donate a proton (H+) in solution. In general, the more stable the conjugate base of an acid, the stronger the acid is. In the case of HOCl and HOI, the strength of the acid is determined by the stability of their respective conjugate bases, ClO- and IO-.

The stability of a conjugate base is affected by the electronegativity and size of the atom that is bonded to the proton. In this case, chlorine (Cl) is more electronegative and smaller than iodine (I). This means that the bond between H and Cl is stronger than the bond between H and I. As a result, the proton in HOCl is less likely to dissociate in solution, making it a weaker acid than HOI.

Additionally, the size difference between Cl and I also affects the stability of the conjugate bases. The larger size of I makes it easier for the negative charge to spread out, making the conjugate base more stable. This leads to HOI being a weaker acid compared to HOCl.

Therefore, based on the strength of the bonds and the stability of the conjugate bases, it can be concluded that HOCl is a stronger acid than HOI. It is important to note that the strength of an acid can also be affected by other factors such as solvent, temperature, and concentration.