Question

Arrange the following compounds in decreasing order of acidity
$H_2O, ROH, HC \equiv CH$

• A. $HC \equiv CH > ROH > H _{2} O$
• B. $H _{2} O > ROH > HC \equiv CH$
• C. $H _{2} O > HC \equiv CH > ROH$
• D. $ROH > H _{2} O > HC \equiv CH$

Answer 1

Answer: (B)

A stronger acid displaces a weaker acid from its salt. Since $H _{2} O$ displaces $ROH$ from $RONa$ and both $H _{2} O$ and alcohol displace acetylene from sodium acetylide, therefore, water is the strongest, followed by alcohol while acetylene is the weakest acid. In other words, acidity decreases in the order:

$H _{2} O > ROH > HC \equiv CH$