What is the pH of a 0.020 mol L^-1 HClO₄ solution? A)0.020 B)0.040 C)1.70 D)12.30

Question

Quizplus · Accepted Answer

HClO is a weak acid and will not completely dissociate in water. To find the pH of the solution, we first need to find the concentration of H+ ions by using the dissociation constant Ka for HClO: Ka = [H+][ClO-]/[HClO]. Since the concentration of HClO is 0.020 mol and it dissociates very little, we can assume that [H+] = [ClO-]. Thus, Ka = [H+]^2/[HClO] = [H+]^2/0.020. 
Using the Ka expression and solving for [H+], we get [H+] = √(Ka*[HClO]) = √(3.10x10^-8*0.020) = 1.77x10^-4 mol/L. 
Using the definition of pH, we get pH = -log[H+] = -log(1.77x10^-4) = 1.70. 
Therefore, the answer is choice C, 1.70.

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