Question

Which of the following orders of acid strength is correct: 

• A. RCOOH > ROH > HOH > HC ≡ CH
• B. RCOOH > HOH > ROH > HC ≡ CH
• C. RCOOH > HOH > HC ≡ CH > ROH
• D. RCOOH > HC ≡ CH > HOH > ROH

Answer 1

The Correct Option is B

 To determine the order of acid strength among the given compounds, we need to understand the concept of acidity in organic chemistry. Acidity is the tendency of a compound to donate a proton (H⁺). The strength of an acid is influenced by the stability of the conjugate base formed after donating the proton.

Let's examine the compounds one by one:

1. Carboxylic acids (RCOOH): These are strong acids compared to alcohols and water because the carboxylate ion (RCOO^-) formed after donating a proton is stabilized by resonance. This stabilizes the negative charge, making them more likely to donate a proton.
2. Water (HOH): Water can act as a weak acid, but its conjugate base (the hydroxide ion, OH^-) is not as stable as the carboxylate ion, which means it is a weaker acid compared to RCOOH.
3. Alcohols (ROH): The alkoxide ion (RO^-) formed from alcohols is destabilized due to the lack of resonance, making alcohols weaker acids than water.
4. Alkynes (HC ≡ CH): These are very weak acids compared to the other groups. The conjugate base, the acetylide ion (HC ≡ C^-), is not stabilized, making alkynes the weakest acids in this group.

Accordingly, the correct order of acid strength is RCOOH > HOH > ROH > HC ≡ CH, where carboxylic acids are the strongest and alkynes are the weakest.

Therefore, the correct answer is:

RCOOH > HOH > ROH > HC ≡ CH