Question

The decreasing order of acidic character of the following is:
I. $C{H}_{3}SH$ II. $C{H}_{3}OH$ III. $H_{2}O$ IV. EtOH

• A. I > II > III > IV
• B. IV > III > II > I
• C. I > III > II > IV
• D. III > I > II > IV

Answer 1

The correct option is A I > II > III > IV

Thiols (RSH ) are more acidic than alcohols. Sulphur is less electronegative than oxygen and S-H bond is weaker than O-H bond. So, releasing of proton is facilitated in case of Thiol due to weak bonding and negative charge is spread over a larger area since atomic size of sulphur is greater than oxygen. Acidity of thiol becomes higher as compare to alcohol.
The conjugate bases of methanol and ethanol are methoxide ion and ethoxide ion, respectively.
methaol is more acidic than water since carbon is more electronegative than hydrogen and stabilizes the anion. However, in ethanol + I effect predominates and ethanol is weakly acidic than water.
$C{H}_{3}SH>C{H}_{3}OH>H_{2}O>C{H}_{3}C{H}_{2}OH$