Acids - What Is An Acid?

What is an acid?

This is an ionic substance which has free Hydrogen ions.

For example when you dissolve HCl in water you get free H+ ions and free Cl- ions.

Water also dissociates into H+ and OH- ions. As there are exactly the same number of H+ and OH- ions in water, water is not acid. OH- ions, when free in solution make the solution alkali. As such, with the same number of OH- as H+, the solution will be neutral.

A solution of NaCl will also be neutral as NaCl contains no free H+ nor OH- ions.

However, some ionic acids don`t dissociate very well and the less well they dissociate makes an acid weaker. But if you put more of the acid solid into the water then the acid is more concentrated. Making an acid less concentrated will not make it neutral but it make lower the pH if you add enough water. You just need to add a lot of water in a strong acid to see an effect.