Multiple Choice
An aqueous solution has a pH of 3.0. Calculate the pOH. Be sure your answer has the correct number of significant digits.
17. Acid and Base Equilibrium
pH of Strong Acids and Bases
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Given the following hydronium ion concentrations at 25°C, calculate the hydroxide ion concentration and classify each solution as acidic or basic: a. [H₃O⁺] = 1.5 × 10⁻³ M, b. [H₃O⁺] = 3.5 × 10⁻⁹ M, c. [H₃O⁺] = 8.3 × 10⁻¹¹ M. Which of the following correctly classifies solution b?
A
[OH⁻] = 2.9 × 10⁻⁵ M, basic
B
[OH⁻] = 2.9 × 10⁻⁵ M, acidic
C
[OH⁻] = 2.9 × 10⁻⁶ M, basic
D
[OH⁻] = 2.9 × 10⁻⁶ M, acidic
Verified step by step guidance1
To find the hydroxide ion concentration [OH⁻] from the hydronium ion concentration [H₃O⁺], use the water dissociation constant at 25°C: Kw = 1.0 × 10⁻¹⁴. The relationship is given by the equation: [H₃O⁺] × [OH⁻] = Kw.
Rearrange the equation to solve for [OH⁻]: [OH⁻] = Kw / [H₃O⁺].
For each given [H₃O⁺], substitute the value into the equation to calculate [OH⁻]. For example, for part a, substitute [H₃O⁺] = 1.5 × 10⁻³ M into the equation.
After calculating [OH⁻] for each solution, compare the concentrations of [H₃O⁺] and [OH⁻] to determine if the solution is acidic or basic. A solution is acidic if [H₃O⁺] > [OH⁻] and basic if [OH⁻] > [H₃O⁺].
For solution b, calculate [OH⁻] using [H₃O⁺] = 3.5 × 10⁻⁹ M. Compare the calculated [OH⁻] with the given options to classify the solution correctly. The correct classification is when [OH⁻] = 2.9 × 10⁻⁶ M, indicating the solution is basic.
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