Multiple Choice
Which of the following accurately describes the pH scale?
17. Acid and Base Equilibrium
The pH Scale
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What is the Kw of pure water at 20.0°C, if the pH is 7.083?
A
8.26 × 10-8
B
6.82 × 10-15
C
7.23 × 10-14
D
1.00 × 10-14
Verified step by step guidance1
Understand that Kw is the ion product of water, which is the product of the concentrations of hydrogen ions [H⁺] and hydroxide ions [OH⁻] in pure water.
Recall that pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration: \( \text{pH} = -\log[H^+] \).
Use the given pH value to find the concentration of hydrogen ions: \( [H^+] = 10^{-\text{pH}} \). Substitute the given pH of 7.083 into this equation.
Since pure water is neutral, the concentration of hydroxide ions [OH⁻] is equal to the concentration of hydrogen ions [H⁺]. Therefore, \( [OH^-] = [H^+] \).
Calculate the ion product of water, Kw, using the formula \( K_w = [H^+][OH^-] \). Substitute the calculated [H⁺] value from step 3 into this equation to find Kw.
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