Difference between the acid strength of inorganic and organic acids

  • Thread starter Rujano
  • Start date
  • #1
Rujano
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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?
 

Answers and Replies

  • #2
AGNuke
Gold Member
455
9
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.
 
  • #3
JohnRC
148
2
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
 
  • #4
AGNuke
Gold Member
455
9
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.
 

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