Question

This is all seriously one question in my review packet.

Concentrated sulfuric acid (18M) is added to water so that the final sulfuric acid concentration is 0.1M. What is the predominant acidic species in this solution. Now add alcohol to this solution to a final concentration of 1M. assuming that the pKa of the protonated alcohol has the same value as the pKa of protonated water, determine the major protonated species in this solution. (please do this conceptually rather than by doing it aritmetically. I want you to be able to look at the data given and make and estimate that you can justify as the predominant species. How would your answer change if you added H2SO4 to methanol (CH3OH)

Answer 1

H₂SO₄ + H₂O H₃O⁺(aq) + HSO₄^-(aq)

The predominant acidic species in the aqueous solution of H₂SO₄ is H₃O⁺(aq).

Now, if you add alcohol to the above solution, then

H₃O⁺(aq) + HSO₄^-(aq) + ROH RO^-(aq) + H₂SO₄(aq) + H₃O⁺(aq)

Therefore, the predominant acidic species is RO^-(aq) since the concentration of ROH(aq) is high.

Now, if you added H₂SO₄ to CH₃OH, then

H₂SO₄(aq) + CH₃OH(aq) H₃O⁺(aq) + HSO₄^-(aq) + CH₃OH(aq)

Therefore, the predominant acidic species is H₃O⁺(aq).