A problem we see students constantly running into is that they do not readily recognize strong acids. This is a terrible mistake and should never happen. You will need to quickly recognize strong acids and which atom they will be protonating. As far as strong acids go, you should immediately recognize the Magnificent Seven:
STRONG ACIDS: HI, HCl, HBr, HNO3, H2SO4, HClO3, H3PO4
Just think that that it’s the three hydrogen halides and the four acids that have N, S, Cl, and P as central atoms. Many students remember the other four acids with the mnemonic, something you would never say to a girlfriend: “Never Say ‘Please Clean’ ”.
Once you have recognized that you have a strong acid present in your reaction, it is necessary to determine what it is protonating. Remember that H+ is electron-deficient (Lewis acidic) and will look for an electron-rich (Lewis basic) atom to protonate. This could be a nitrogen atom, such as an amine, or an oxygen atom in a carbonyl or an alcohol. Most often, the atom being protonated will have a lone pair somewhere.
Take Home Message: Know the strong acids, the mnemonic Never Say ‘Please Clean’ might help
Dr. Michael Pa
Dr. Michael Pa got a bachelors degree in chemistry from Binghamton University, a masters degree in organic chemistry from the University of Arizona and a Ph.D. in organic chemistry from the University of Arizona. His research focus was on novel pain killers which were more potent than morphine but designed to have fewer side effects. There may even be a patent or two that came out of it. Prior to all of this, he was a chemist at Procter and Gamble. After all of that, he (briefly) worked as a post-doctoral assistant at Syracuse University, working on novel organic light-emitting diodes (OLEDs). In between, he did NOT compete at the 1996 Olympics, make the Atlanta Braves opening day roster, or become the head coach of the Indiana Pacers, as he had intended. #fail During this entire time, he always loved helping students, especially if they were struggling with organic chemistry. In 2006, Dr. Pa founded AceOrganicChem.com in order to make learning organic chemistry fast and easy. 14 years and about 60,000 students later we are still helping students to learn organic chemistry one reaction at a time at https://www.aceorganicchem.com
H3PO4 is not a strong acid. The Ka for H3PO4 is 7.5 x 10^-3 which makes it a relatively weak acid. The seventh strong acid is HClO4.