## 6C.21b

Acidity $K_{a}$
Basicity $K_{b}$
The Conjugate Seesaw $K_{a}\times K_{b}=K_{w}$

Joanne Kang 3I
Posts: 50
Joined: Thu Jul 25, 2019 12:17 am

### 6C.21b

Suggest an explanation for the different strengths of (b) acetic acid and formic acid.

Sears 4A
Posts: 36
Joined: Tue Feb 05, 2019 12:15 am

### Re: 6C.21b

"Out of acetic acid and formic acid, formic acid is considered stronger because the CH3 in acetic acid is electron donating. The CH3 actually contributes electron density towards the O-H bond, making it harder to remove the H, and making acetic acid a weaker acid than formic acid."

Drake Choi_1I
Posts: 58
Joined: Sat Aug 17, 2019 12:15 am

### Re: 6C.21b

How can we tell that acetic acid is electron donating?

Hannah Lee 2F
Posts: 117
Joined: Thu Jul 11, 2019 12:15 am

### Re: 6C.21b

If you draw out the Lewis structure, the main difference between the two groups is that acetic acid has a methyl group (CH3) where formic acid only has H. Thus, CH3COOH has an e- donating group, CH3, that destabilizes the negative charge of the resulting anion by contributing e- density. This means that the negative charge is less spread out over the anion (less delocalization), making it less stable, so that the H+ is less likely to be donated --> less acidic. Formic acid, on the other hand, does not have an e- donating group so the O-H bond is a little more polar (easier for the acidic hydrogen to be donated to H2O to form H3O+), making it more acidic overall.

Here's another explanation that is probably clearer: https://www.quora.com/Which-is-the-stro ... id-and-why