Is acidity a property or a change?

Answer 1

pH is another measure for concentration: that's physical.

But it is the result of a chemical reaction in water: protolysis of acid and base molecules.

Answer 2

Yes! because if you want to test it (like mixing backing soda and vinegar) you change the chemical identity of the substance.

Answer 3

It is a chemical found in common, everyday foods such as: Orange juice, Oranges, pinaples,...