Which one of the following statements is true for a 0.1 M solution of a weak acid HA A) The concentration of H⁺ is slightly greater than the concentration of A^-. B) The pH equals 1.0. C) The concentration of H⁺ is exactly equal to the concentration of A^-. D) The pH is less than 1.0. E) The concentration of H⁺ is slightly less than the concentration of A^-.

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Quizplus · Accepted Answer

A weak acid, HA, will not fully dissociate in water. The equilibrium reaction for this weak acid would be: HA + H2O ⇌ H3O+ + A- Therefore, at equilibrium, there will be a mixture of four species present: HA, H3O+, A-, and H2O. The ratio of the concentrations of the acid and its conjugate base will depend on the acid's dissociation constant, Ka, and the initial concentration of the acid. As a general rule, the pH of a weak acid solution will be less than 7.0. Therefore, choice B and D can be eliminated. Additionally, since HA is a weak acid, its dissociation will be less than 100%. Therefore, the concentration of H⁺ will not be equal to the concentration of A^-. This eliminates choice C. The only possible option is A, which states that the concentration of H⁺ is slightly greater than the concentration of A^-. This is because the weak acid is only partially dissociated into H3O+ and A-.

Which One of the Following Statements Is True for a 0.1