Oxoacid strengths in aqueous solutions

[Mangoes]

Hey there,

My textbook doesn't expand on this much and I'm unsure if I'm just not seeing some obvious connection; I'd appreciate it if someone could clarify this for me.

I'm studying the Bronsted-Lowry theory and the strength of binary and ternary acids. I understand how, for example, H₂SO₄ dissociates in water, but I don't see why the dissociation of that would be any different than say, H₂SO₃.

I realize that for some reason, acid strength increases with an increased number of oxygen atoms, but I can't understand why.

From what I understand, the O-H bonds are broken in water to create an anion and H⁺, so why would a larger amount of oxygen atoms in a molecule have anything to do with acid strength since the amount of O-H groups remain constant in both molecules (for example, H₂SO₄ and H₂SO₃ both have the same amount of O-H groups.)

What am I misunderstanding or missing?

 

[Zefram]

Hello there,

Thank you for reaching out with your question about the Bronsted-Lowry theory and acid strength. It is great that you are trying to understand the concept better and I am happy to clarify it for you.

Firstly, it is important to understand that the strength of an acid is determined by its ability to donate a proton (H+) in an aqueous solution. The more easily an acid can donate a proton, the stronger it is considered to be.

Now, let's look at the specific example you mentioned with H2SO4 and H2SO3. Both of these molecules have the same number of O-H bonds, but the difference lies in the strength of the bonds. In H2SO4, the sulfur atom is bonded to four oxygen atoms, which leads to a more polarized and weaker O-H bond. This makes it easier for the proton to be released, thus making H2SO4 a strong acid. On the other hand, in H2SO3, the sulfur atom is bonded to only three oxygen atoms, resulting in a stronger and less polarized O-H bond. This makes it more difficult for the proton to be released, making H2SO3 a weaker acid.

In general, the more oxygen atoms an acid has, the more polarized and weaker the O-H bond becomes, making it easier for the proton to be released and increasing the acid strength. This is why acids with more oxygen atoms, such as H2SO4, are stronger than those with fewer oxygen atoms, like H2SO3.

I hope this explanation helps to clarify the concept for you. If you have any further questions, please don't hesitate to ask. Keep up the good work in your studies!