Question

Which solution has the lowest pH?

1.0 M HNO2
1.0 M CH3COOH
1.0 M HCOOH
1.0 M HNO3
1.0 M HPO4–

Answer 1

The correct option is 1.0 M HNO₃

Step-by-step explanation:

The substance with the lowest pH (closest to zero pH) has to be a strong acid. A strong acid is an acid whose hydrogen atom(s) completely ionized in water.

Another factor can affect the pH of a solution, which is concentration. When the concentration of an acid (weak or ) is high in a solution, the pH of the solution decreases. However, all the options provided have the same concentration

The only strong acid in the question is HNO₃ and since they all have the same concentration, HNO₃ is the correct answer.

NOTE: A weak acid is an acid whose hydrogen atom(s) partially ionized in water.

Answer 2

The solution with the lowest pH is HPO4-. It is also a weak acid and is only partially ionized. The lowest pH means the most acidic. The only strong acid is HNO3, nitric acid, which is 100% ionized. HNO3(aq) ====> H+ + NO3-