What is the hydronium ion concentration in a solution prepared by mixing 50.00 mL of 0.10 M HCN with 50.00 mL of NaCN? Assume that the volumes of the solutions are additive and that K_a = A) 2.0 × 10^-¹⁰ M B) 4.9 × 10^-10 M C) 1.2 × 10^-⁹ M D) 7.0 × 10^-6 M

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Quizplus · Accepted Answer

The balanced chemical equation for the reaction between HCN and NaCN in water is: HCN + NaCN + H2O -> H3O+ + CN- + Na+ Since Na+ is a spectator ion and does not participate in the acid-base equilibrium, we can ignore it in our calculations. The initial concentrations of HCN and CN- are given by: [HCN] = 0.10 M [CN-] = 0.10 M * (50.00 mL / 100.00 mL) * (1 L / 1000 mL) / K_a = 9.1 × 10^-10 M (using the given value of K_a = 3.9 × 10^-10) Assuming that the solution is well-mixed and the volume does not change upon mixing, the final volume is 100.00 mL and the final concentration of H3O+ is given by: [H3O+] = [CN-] + Ka * [HCN] = 9.1 × 10^-10 M + (1.0 × 10^-9) * (0.10 M) = 1.2 × 10^-9 M Therefore, the hydronium ion concentration in the solution is 1.2 × 10^-9 M, which is closest to choice (C).

What Is the Hydronium Ion Concentration in a Solution Prepared