Difference between the acid strength of inorganic and organic acids

[Rujano]

Homework Statement

Hi. I'm pretty much a beginner in organic chemistry and I'm just wondering something.

For example, I know that HCl is a stronger acid than HF.

But... then why the following happens if a have an organic acid (e.g a carboxylic acid)?

According to what I see, a carboxylic acid with a Cl substitutent is weaker than one with a F substituent.

Homework Equations

The Attempt at a Solution

I also know that because of electronegativity the difference between H and F is higher than that of H and Cl. So, that means that the bond between H and F is stronger, and therefore, the compoud is weaker ... am I right?

 

[AGNuke]

All Organic acids are weak acid (Generally). To determine the acidic strength, try forming their conjugate base on paper. Check their stability.

For F and Cl substituted Carboxylic acid, F exerts its inductive effect more than Cl, so it stabilizes the conjugate base by shifting the negative charge from -COO group to a wider area.

 

[JohnRC]

There is a huge difference in the trend in acid strength if we are looking at the atom directly bonded to the acidic hydrogen, or a more remote atom.
For directly bonded atoms:
HI > HBr > HCl > HF
H₂Se > H₂S > H₂O

For more remote atoms:
HONO₂ > HOPO₂
HOSO₂OH > HOSeO₂OH

Organic acids also follow this latter trend:

CH₂F.COOH > CH₂Cl.COOH > CH₃.COOH

 

[AGNuke]

The trend depends majorly on the stability of conjugate base. The better the CB is able to handle the negative charge on itself, the more acidic the acid. Simple Enough.