Question

What is the purpose of adding sufuric acid at the end of the Gringard reaction??

Answer 1

It depends. You may be talking about a grignard attacking a carbonyl carbon.

If so, then it is likely that a tetrahedral intermediate forms; to finish the reaction from there, there is a negatively-charged carbonyl oxygen whose `pi` bond was broken due to the grignard nucleophile's bonding, and that oxygen can grab a proton from an acid of some sort.

If there are no leaving groups that can leave easily, then nothing can happen if you don't add anything else to the reaction. In a case like that, a strong acid is recommended to finish the reaction. Sulfuric acid is a strong acid `(pKa ~~ -3 => K_a ~~ 1000)`, so it is a reasonable choice sometimes to use it to finish the reaction.

Note: This tends to be part of a lab you do early in the year for Organic Chemistry II. I think you should ask your professor if you have questions about your lab, because they will be around.