# Why HNO3 acid is stronger than H3PO4?

$$\ce{H3PO4}$$ can donate 3 protons on the other hand $$\ce{HNO3}$$ can donate 1 proton. So that makes $$\ce{H3PO4}$$ stronger isn't it? But my book says $$\ce{HNO3}$$ is stronger without any explanation.

• Think of it as the difference between throwing several small pebbles and one single cannonball. If you need to break down a wall, probably only the latter will do. – Nicolau Saker Neto Jul 20 at 10:14
• Acid strength is a measure of how readily the first proton is donated. It is more readily donated by nitric acid than phosphoric. – Waylander Jul 20 at 10:26
• Ok so nitrogen donates proton easily.Sir, can you please describe why the donation for nitric acid is easier than phosphoric acid? – Ghost Jul 20 at 11:51
• Nitric acid pKa = −1.4, phosphoric acid pKa1 = 2.15; pKa2 = 7.09; pKa3 = 12.32 // In chemistry at first focus on the facts, the behavior of the chemicals. Ask why questions later. A lot of the why explanations in freshman chemistry are over simplifications. – MaxW Jul 20 at 13:10
• chemistry.stackexchange.com/questions/96618/… – Mithoron Jul 20 at 17:27

Draw the ions of respective acids. See which one becomes more stable. Nitric acid $$\ce{N}$$ is in a bad state with a positive charge. it's a highly eletronagative atom near oxygen becoming negative will become more stable. See also what happens with $$\ce{H3PO4}$$. $$\ce{P}$$ is not eletronegative as $$\ce{N}$$ so it doesn't care much as $$\ce{N}$$ for $$\ce{O}$$ becoming negative. See you will then understand the more stable ion of the respective acid want to get rid of the $$\ce{H}$$ atom badly meaning more acidic. Draw the ions you will understand then.