5HNO3 represents five molecules of nitric acid (HNO3), which is a strong mineral acid commonly used in chemical synthesis. Each molecule of nitric acid contains one nitrogen atom, one oxygen atom, and three hydrogen atoms.
When 3P + 5HNO3 produces 2H2O+ 5NO +3 H3PO4then elemental Phosphorus is oxidized by taking 5 electrons (to become P(+5) in H3PO4) from N(+5)atom in HNO3 (which is turned into N(+2) in NO)
it may produces explosive material if not stabilized
Potassium dichromate reacts with nitric acid to form chromium(III) nitrate, nitrogen dioxide gas, and water. The balanced chemical equation for this reaction is: 3K2Cr2O7 + 8HNO3 → 3Cr(NO3)3 + 3KNO3 + 4H2O + 3NO2.
Pieces of copper are added to hot concentrated solutions of hydrochloric, phosphoric, sulfuric and nitric acids. A reaction clearly takes place between copper and nitric acid. The presence of copper ions can be observed by adding each solution to a dilute solution of ammonia. If copper ions were present, we would see the blue color of the copper-ammonia complex. Sulfuric acid has oxidized the copper metal, as indicated by the blue color. Nitric acid is a stronger oxidizing agent (and produces a higher concentration of copper(II) ions), as indicated by the darker blue color.