Question

question
a sample of carbon dioxide in water at room temperature has a hydroxide ion concentration of 7.9×10⁻⁸ m. what is the hydronium ion concentration of the solution?
select the correct answer below:
○ 2.4×10⁻⁸ m
○ 9.8×10⁻⁷ m
○ 5.6×10⁻⁶ m
○ 1.3×10⁻⁷ m

Explanation:

Step1: Recall the ion - product constant of water

At room temperature, \(K_w = [H_3O^+][OH^-]=1.0\times 10^{-14}\)

Step2: Solve for \([H_3O^+]\)

We know \([OH^-]=7.9\times 10^{-8}\space M\). Rearranging the formula \(K_w = [H_3O^+][OH^-]\) gives \([H_3O^+]=\frac{K_w}{[OH^-]}\)
Substitute \(K_w = 1.0\times 10^{-14}\) and \([OH^-]=7.9\times 10^{-8}\) into the formula:

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Answer:

\(1.3\times 10^{-7}\space M\) (the fourth option)