Which change in the concentration of H3O+ ions results in a decrease of one unit in the pH value for an aqueous solution?

Regents Chemistry Exam June 2025 Question 27

27 Which change in the concentration of H3O+ ions results in a decrease of one unit in the pH value for an aqueous solution?

(1)  a decrease in the concentration of H3O+ by a factor of 10

(2)  a decrease in the concentration of H3O+ by a factor of 1

(3)  an increase in the concentration of H3O+ by a factor of 10

(4)  an increase in the concentration of H3O+ by a factor of 1

Solution:

When pH decreases, this means the solution becomes MORE acidic, and the concentration of hydronium ions increases. Every 1 pH unit represent a factor of 10. To decrease pH by 1, hydronium ion concentration needs to increase by a factor of 10. Choice 3 is the correct answer.

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