Question

An unknown weak acid with a concentration of 0.530 M has a pH of 5.600. What is the Ka of the weak acid

Answer 1

Answer:

Ka = 3.45x10⁻⁶

Explanation:

First we calculate [H⁺], using the given pH:

• pH = -log[H⁺]

• [H⁺] = $10^{-pH}=10^{-5.6}$

• [H⁺] = 2.51x10⁻⁶ M

To solve this problem we can use the following formula describing a monoprotic weak acid:

• [H⁺] = $\sqrt{C*Ka}$

We input the data that we already know:

• 2.51x10⁻⁶ = $\sqrt{0.530*Ka}$

And solve for Ka:

• Ka = 3.45x10⁻⁶