A weak acid has K_a = 4.2 × 10^-3.If [A^-] = 2.0 M,what must [HA] be so that [H⁺] = 2.1 × 10^-3 M? A)1.5 M B)2.0 M C)1.0 M D)0.5 M E)0.25 M

Question

Quizplus · Accepted Answer

Using the equilibrium constant expression for the dissociation of the weak acid: K_a = [H⁺][A^-]/[HA] Substituting the given values, we get: 4.2 × 10^-3 = (2.1 × 10^-3) (2.0)/(HA) Solving for [HA], we get: [HA] = (2.1 × 10^-3) (2.0)/(4.2 × 10^-3) = 1.0 M Therefore, the answer is C.

A Weak Acid Has Ka = 4

A Weak Acid Has K_a = 4