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Ch.16 - Acids and Bases
Chapter 16, Problem 57b

For each strong acid solution, determine [H3O+], [OH], and pH. b. 0.015 M HNO3

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<strong>Step 1:</strong> Recognize that HNO<sub>3</sub> is a strong acid, which means it completely dissociates in water. Therefore, the concentration of H<sub>3</sub>O<sup>+</sup> ions will be equal to the initial concentration of the acid, which is 0.015 M.
<strong>Step 2:</strong> Use the relationship between the concentrations of H<sub>3</sub>O<sup>+</sup> and OH<sup>-</sup> ions in water, given by the ion product of water: K<sub>w</sub> = [H<sub>3</sub>O<sup>+</sup>][OH<sup>-</sup>] = 1.0 x 10<sup>-14</sup> at 25°C.
<strong>Step 3:</strong> Calculate the concentration of OH<sup>-</sup> ions using the formula: [OH<sup>-</sup>] = K<sub>w</sub> / [H<sub>3</sub>O<sup>+</sup>]. Substitute the known values to find [OH<sup>-</sup>].
<strong>Step 4:</strong> Determine the pH of the solution using the formula: pH = -log[H<sub>3</sub>O<sup>+</sup>]. Substitute the concentration of H<sub>3</sub>O<sup>+</sup> to find the pH.
<strong>Step 5:</strong> Review your calculations to ensure that the values for [H<sub>3</sub>O<sup>+</sup>], [OH<sup>-</sup>], and pH are consistent with the properties of a strong acid solution.

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Key Concepts

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

Strong Acids

Strong acids, such as HNO3 (nitric acid), completely dissociate in water, meaning that all the acid molecules break apart into their constituent ions. This results in a high concentration of hydronium ions ([H3O+]) in solution, which is crucial for calculating pH and hydroxide ion concentration ([OH-]).
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pH Calculation

The pH of a solution is a measure of its acidity, calculated using the formula pH = -log[H3O+]. For strong acids, the concentration of hydronium ions is equal to the molarity of the acid solution, allowing for straightforward pH calculations. A lower pH value indicates a more acidic solution.
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Water Ion Product

The water ion product (Kw) is the equilibrium constant for the self-ionization of water, defined as Kw = [H3O+][OH-] = 1.0 x 10^-14 at 25°C. This relationship allows for the determination of hydroxide ion concentration ([OH-]) from the known hydronium ion concentration, using the equation [OH-] = Kw / [H3O+].
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