Question

How many protons do you think are dissociable from propionic acid and butyric acid? Explain your reasoning.

Answer 1

Answer:

One

Explanation:

The formulas for the two acids are CH₃CH₂COO-H and CH₃CH₂CH₂COO-H.

The key factors to consider are the polarities of the C-H and O-H bonds.

A. C-H bonds

The difference in electronegativity is ΔEN =|2.55 - 2.20| = 0.35.

This difference of so small that we usually consider the C-H bond to be nonpolar.

It is extremely unlikely that a C-H bond will dissociate onto ions.

B. O-H bonds

The difference in electronegativity is ΔEN =|3.44 - 2.20| = 1.24.

Thus, an O-H bond is highly polar covalent — the bond has about 32 % ionic character.

It is much more likely that an O-H bond will go all the way and dissociate onto ions.

RCOOH + H₂O ⇌ RCOO⁻ + H₃O⁺

The Kₐ for an O-H bond is about 10⁴⁶ times that of a C-H bond.

Only the O-H bond of a carboxylic acid will dissociate,