A 0.01 M solution of an acid has pH = 5.0. What is the Ka value?
Answer:
⇒ Ka = 1 x 10-8.
Explanation:
Acids are proton donors that get ionized to release H+ ions in water.
⇒ Considering pH 5.0, we assume that the acid given above is a monoprotic weak acid, i.e., it partially dissociates in an aqueous solution to produce a single H+ ion per HA molecule, as shown below.
HA (aq) ⇌ A– (aq) + H+(aq)………… Equation 1
⇒ An H+ ion combines with an H2O molecule to form a hydronium (H3O+) ion in an acidic solution.
⇒ The concentration of hydronium [H3O+] ions present in the solution determines its acidic strength. The higher the [H3O+], the lower the pH and the greater the strength of the acidic solution.
pH of the acidic solution = -log[H+]
or
pH = -log [H3O+] …………Equation 3
⇒ Rearranging equation 3 to make [H3O+] the subject of the formula.
[H3O+] = 10-pH ……. Equation 4
⇒ As the pH of the solution is given, i.e., pH = 5.0. So we can use equation 4 to determine the concentration of hydronium ions formed in the 0.01 M acidic solutions.
[H3O+] = 10-5.0 = 1 x 10-5 M.
⇒ As per equation 2, at equilibrium,1 mole of an acid (HA) dissociates to produce an equal concentration of A– (the conjugate base) and H3O+ (hydronium ions).
∴ So in our case, at equilibrium [H3O+] = [A–] = 1 x 10-5 M.
The initial HA concentration decreases to produce A– and H3O+ ions in the aqueous solution.
An equilibrium is achieved when there is no further change in concentrations at either the reactant and/or the product side.
⇒ The equilibrium constant for the dissociation of a weak acid in an aqueous solution is known as the acid dissociation constant, i.e., Ka.
My name is Vishal Goyal and I am the founder of Topblogtenz. I hold a degree in B.tech (Chemical Engineering) and have a strong passion for the life sciences and chemistry. As a highly qualified and experienced chemistry tutor with 4 years of experience, I possess a deep understanding of the unique challenges that students often encounter when attempting self-study in the field of chemistry. I have created this website as a comprehensive resource for those who are seeking guidance and support in their chemistry studies. I have brought together a team of experts, including experienced researchers, professors, and educators, to provide our readers with accurate and engaging information on a wide range of chemistry and science topics. Our goal is to make complex subjects like chemistry accessible and understandable for all. I hope you find the information and resources on our site helpful in your studies. Let's connect through LinkedIn: https://www.linkedin.com/in/vishal-goyal-2926a122b/