Question

The acid-dissociation constant for chlorous acid, hclo2, at 25ec is 1.0 ˛ 10-2. calculate the concentration of h if the initial concentration of acid is 0.100 m?

a) 0.010 M
b) 0.025 M
c) 0.050 M
d) 0.100 M

Answer 1

The concentration of hydrogen ions (H+) in a 0.100 M chlorous acid solution with a Ka of 1.0 × 10⁻² is approximately 0.010 M, corresponding to answer option (a).

Step-by-step explanation:

The question involves calculating the concentration of hydrogen ions (H+) in a solution of chlorous acid (HClO2) with an initial concentration of 0.100 M, given that the acid-dissociation constant (Ka) is 1.0 × 10⁻² at 25°C. We can use an ICE table to track the initial concentrations, changes in concentration, and equilibrium concentrations of the reactants and products.

Initial concentrations (M): [HClO2] = 0.100, [H+] = 0, [ClO2⁻] = 0
Changes in concentration (M): [HClO2] = -x, [H+] = +x, [ClO2⁻] = +x
At equilibrium (M): [HClO2] = 0.100 - x, [H+] = x, [ClO2⁻] = x

Substituting equilibrium concentrations into the expression for Ka, we get:
Ka = [H+][ClO2⁻]/[HClO2] = (x)(x)/(0.100 - x)
1.0 × 10⁻² = (x²)/(0.100 - x)

Since Ka is quite large (compared to more weakly dissociating acids), we cannot assume that x is negligibly small. We therefore need to solve the quadratic equation for x, the [H+] concentration.
After solving, one might find that the concentration of HClO2 changes very slightly, and thus the approximation is reasonable, and x is approximately 0.010 M. Therefore, the correct answer would be (a) 0.010 M.