Question

Rank these acids in order of acidity (from most to least) and briefly explain why?

H2F+
(CH3)2OH+
CH3OH
CH3SH2+

Answer 1

Order of acidity from greatest to least.

H2F+ => CH3SH2+ => (CH3)2OH+ => CH3OH

Here is an explanation I found searching for an answer to the above question.

"The ionization process depends upon the breaking of the bond to hydrogen, so the weaker the H–X bond, the stronger the acid. Bond energies usually decrease down a group, because the distance between nuclei increases. The element effect gives the acidity ranking H2F > CH3SH2 > (CH3)2OH . The charge effect makes CH3OH the least acidic. The reason that H2F is more acidic than CH3SH2 is that HF is more acidic than CH3SH. The charge effect should make both more acidic, and we assume that it should not change their relative order."

Answer 2

Order of acidity (from most to least):
`H_(2)F^(+)>(CH_(3))_(2)OH^(+)>CH_(3)SH_(2)^(+)>CH_(3)OH`

Step-by-step explanation:

Electronegativity order : F > O > S

Proton attached with more electronegative atom will be more acidic. Because the bonding electron cloud lies majorly over electronegative atom and, hence, proton can be easily removed during acid-base reaction.

Therefore
`H_(2)F^(+)` is most acidic.

`(CH_(3))_(2)OH^(+)` is second most acidic as proton is attached to positively charged oxygen atom.

`CH_(3)SH_(2)^(+)` is third most acidic because here proton is attached to positively charged S atom. Positive charge predominates over electronegativity difference between O and S atom.

`CH_(3)OH` is least acidic as it is a neutral molecule.

Order of acidity (from most to least):
`H_(2)F^(+)>(CH_(3))_(2)OH^(+)>CH_(3)SH_(2)^(+)>CH_(3)OH`