August 2018 NY Regents Chemistry Exam
49 Compared to a 1.0-liter aqueous solution with a pH of 7.0, a 1.0-liter aqueous solution with a pH of 5.0 contains (1) 10 times more hydronium ions
(2) 100 times more hydronium ions
(3) 10 times more hydroxide ions
(4) 100 times more hydroxide ions
Solution: As the pH decreases, the concentration of H+ or H3O+ (hydronium ion) increases and the concentration of OH- (hydroxide ion) decreases (solution is becoming more basic and less acidic). How much does the concentration change? Each pH unit is equal to a factor of 10. Going from pH 7-5 = 2 units, means 10*10 = 100. This means there is 100 time more hydronium ions.
Answer: 2
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