What is pH of a substance?

Answer 1

The pH of a substance tells if it's an acid, neutral, or a base. With all deference to the asker and to the previous answerer, technically substances don't have pH's. Aqueous solutions have pH's, and the pH tells you (on a logarithmic scale) the concentration of H+ (or more precisely H3O+) in that solution. A substance is an acid if it lowers the pH of a solution when it is dissolved. It does this by donating protons (H+'s) to water molecules to create more H3O+. A substance is a base if it increases the pH of a solution by accepting a proton from water molecules to form OH-. H3O+ and OH- are in equilibrium with each other in solution, so the more OH- you create, the less H3O+ will be in solution and the higher the pH. So a better answer to the question is that "The pH of a solution tells you if its an acidic, neutral, or basic solution."

Answer 2

pH is a measure of how acidic or basic a substance is on a scale of 0 to 14. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic. The lower the pH value, the more acidic the substance, and the higher the pH value, the more basic it is.