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Ch.16 - Aqueous Equilibria: Acids & Bases
McMurry - Chemistry 8th Edition
McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook
All textbooksMcMurry 8th EditionCh.16 - Aqueous Equilibria: Acids & BasesProblem 6
Chapter 16, Problem 6

What is the pH of an aqueous solution of Ca1OH22 at 25.0 °C with a concentration of 6.3 * 10-5 M? (LO 16.7) (a) 4.20 (b) 10.10 (c) 11.36 (d) 9.80

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1
Identify the chemical formula: The given compound is Ca(OH)_2, which is calcium hydroxide, a strong base.
Determine the dissociation: Ca(OH)_2 dissociates in water to form Ca^{2+} and 2 OH^- ions. The balanced equation is: Ca(OH)_2 \(\rightarrow\) Ca^{2+} + 2 OH^-.
Calculate the concentration of OH^- ions: Since each formula unit of Ca(OH)_2 produces 2 OH^- ions, the concentration of OH^- ions is 2 times the concentration of Ca(OH)_2. Therefore, [OH^-] = 2 \(\times\) 6.3 \(\times\) 10^{-5} M.
Calculate the pOH: Use the formula pOH = -\(\log\)[OH^-] to find the pOH of the solution.
Determine the pH: Use the relationship pH + pOH = 14 to find the pH of the solution.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

pH Scale

The pH scale measures the acidity or basicity of a solution, ranging from 0 to 14. A pH of 7 is neutral, below 7 indicates acidity, and above 7 indicates basicity. The pH is calculated as the negative logarithm of the hydrogen ion concentration, pH = -log[H+]. Understanding the pH scale is essential for determining the nature of the solution in the given question.
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The pH Scale

Hydroxide Ion Concentration

In a basic solution, the concentration of hydroxide ions (OH-) is crucial for calculating pH. For calcium hydroxide, Ca(OH)2, it dissociates in water to produce calcium ions and hydroxide ions. The concentration of hydroxide ions can be determined from the concentration of the calcium hydroxide solution, which directly influences the pH calculation.
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Hydroxide Ion Concentration Example

Ion Product of Water

The ion product of water (Kw) at 25 °C is 1.0 x 10^-14, which relates the concentrations of hydrogen ions and hydroxide ions in water. This relationship is expressed as Kw = [H+][OH-]. Knowing Kw allows us to find the hydrogen ion concentration from the hydroxide ion concentration, which is necessary for calculating the pH of the solution in the question.
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Related Practice
Textbook Question
What is the concentration of hydroxide ions 3OH-4 in a glass of wine with pH = 3.64? (LO 16.5, 16.6) (a) 2.3 * 10-4 M (b) 6.4 * 10-3 M (c) 6.8 * 10-9 M (d) 4.4 * 10-11 M
Textbook Question
An acid solution with a concentration of 0.500 M has a pH = 3.21. What is the Ka of the acid? (LO 16.8) (a) 1.2 * 10-5 (b) 1.7 * 10-6 (c) 7.6 * 10-7 (d) 5.4 * 10-3
Textbook Question
Consider the conjugate bases, 1X-, Y-, Z-2 in Problem 2. If you mix equal concentrations of reactants and products, which of the following reactions will proceed to the left? (LO 16.3) (a) HX + Y- HY + X- (b) HX + Z- HZ + X- (c) HY + X- HX + Y- (d) HZ + Y- HY + Z-

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Textbook Question
Which is the strongest acid? (LO 16.4) (a) HClO3 (b) HBrO3 (c) H2SO3 (d) H2TeO3
Textbook Question
Ammonia 1NH32 has base dissociation constant 1Kb2 of 1.8 * 10-5. What is the concentration of an aqueous ammonia solution that has a pH of 11.68? (LO 16.11) (a) 0.28 M (b) 3.6 M (c) 9.0 * 10-3 M (d) 1.3 M
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