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Ch.10 Acids and Bases and Equilibrium
Timberlake - Chemistry: An Introduction to General, Organic, and Biological Chemistry 14th Edition
Timberlake14thChemistry: An Introduction to General, Organic, and Biological ChemistryISBN: 9781292472249Not the one you use?Change textbook
Chapter 10, Problem 34a

Calculate the [H3O+] of each aqueous solution with the following [OH-]:
a. baking soda, 1.0 × 10-6 M

Verified step by step guidance
1
Step 1: Recall the relationship between [H₃O⁺] and [OH⁻] in aqueous solutions, which is given by the ion-product constant for water: K_w = [H₃O⁺][OH⁻]. At 25°C, K_w = 1.0 \times 10^{-14}.
Step 2: Rearrange the equation to solve for [H₃O⁺]: [H₃O⁺] = \frac{K_w}{[OH⁻]}.
Step 3: Substitute the given value of [OH⁻] into the equation. For baking soda, [OH⁻] = 1.0 \times 10^{-6} \text{ M}. The equation becomes: [H₃O⁺] = \frac{1.0 \times 10^{-14}}{1.0 \times 10^{-6}}.
Step 4: Simplify the expression by dividing the values in the numerator and denominator. Use the rules of exponents: \frac{10^{-14}}{10^{-6}} = 10^{-14 + 6} = 10^{-8}.
Step 5: Conclude that the [H₃O⁺] for the solution is 1.0 \times 10^{-8} \text{ M}. This indicates the solution is slightly basic, as [H₃O⁺] is less than 1.0 \times 10^{-7} \text{ M}.

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Key Concepts

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

pH and pOH Relationship

The pH and pOH of a solution are related through the equation pH + pOH = 14 at 25°C. This relationship allows us to calculate one from the other. Since pH measures the concentration of hydrogen ions [H₃O⁺] and pOH measures the concentration of hydroxide ions [OH⁻], knowing one enables the determination of the other, which is essential for understanding acid-base chemistry.
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Ion Product of Water (Kw)

The ion product of water (Kw) is a constant that equals 1.0 x 10⁻¹⁴ at 25°C, representing the product of the concentrations of hydrogen ions [H₃O⁺] and hydroxide ions [OH⁻]. This means that in any aqueous solution, the product of [H₃O⁺] and [OH⁻] will always equal Kw. This concept is crucial for calculating the concentration of [H₃O⁺] when [OH⁻] is known.
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Calculating [H₃O⁺] from [OH⁻]

To find the concentration of hydronium ions [H₃O⁺] from a given concentration of hydroxide ions [OH⁻], you can use the formula [H₃O⁺] = Kw / [OH⁻]. By substituting the known value of [OH⁻] into this equation, you can determine the corresponding [H₃O⁺] concentration, which is essential for understanding the acidity of the solution.
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