How to determine?

Question

Hey,

I am studying for this chemistry exam, and am quite confused with this acidic concept. In particular, the prompt asks:

In which of the following pairs is the first compound more acidic?

a. HCl HBr

b. HClO2 HBrO2

c. HNO3 H2SO3

d. A and B

e. B and C

The correct answer is E. I understand that HNO3 is a strong acid, but what maces choice B stronger then choice A? I know that HBr is stronger because it is a bigger element, but Isnt answer B the exact same?

Or am I missing something?

Thanks in advance

So........When there is no bonding with Oxygen, then a compound is more acidic based on size? When you are bonding with O, then it goes by electronegativity?

Answer 1

I am not going to attempt to answer the first Q as I am not clear on substances A, B, C.

But the acidity is depending on how easy it is to split a H+ off. This is easier, the more polar bond the bond to the hydrogen is.
Obviously, the size of an atom is connected to its electronegativity ; the smaller ther closer outer e- to the core and the higher the electronegativity.
[Very strongly electronegative elements can assert a "pull" of bond electrons over one or two partners.] Hope that helped you in answering the question.

Answer 2

The reason B and C are the strongest is because of the presences of Oygen atoms.

The HXO acids like B and C form the respective ClO2(-1) ion , BrO2(-1) ion, etc.

These ions are highly stable.

The structure is O-Cl-O and O-Br-O respectively. Each oxygen has a set of 3 lone pairs. The Cl also has 2 lone pairs as well. The oxygen atoms have a charge of -1 and the Cl has a charge of +1. The total charge on the molecule is -1 (-1 + (+1) + (-1) ). The reason the molecule is so stable is because the negative charges on the O atoms are stabilized by the Cl atom. The Cl atoms are more electronegative and O doesn't quite like to bear negative charge. The chlorine helps because it pulls electrons from both O atoms onto itself.

The same occurs with the polyoxygenated acids except this time the charge on O is spread out through resonance. The extra electrons on one of the O atoms is spread throughout the molecules to the other O atoms.

Answer 3

Chlorine is more electronegative than bromine, so H-O-ClO is more acidic than H-O-BrO.