Question

What is the hydronium ion concentration in a solution prepared by mixing 150.00 ml of 0.10 mhcn with 150.00 ml of 0.030 mnacn? assume that the volumes of the solutions are additive and that ka=4.9×10−10. what is the hydronium ion concentration in a solution prepared by mixing 150.00 of 0.10 with 150.00 of 0.030 ? assume that the volumes of the solutions are additive and that . 4.9×10−10m 7.0×10−6m 1.6×10−9m 2.4×1010m?

Answer 1

Answer is: 1.6×10−9m.
This is buffer solution, so use Henderson–Hasselbalch equation: 
V(solution) = 150 mL + 150 mL = 300 mL ÷ 1000 mL/L = 0.3 L.
c(HCN) = ck = 0.15 L · 0.1 M / 0.3 L = 0.05 M.
c(NaCN) = cs = 0.15 L · 0.03 M / 0.3 M = 0.015 M.
[H⁺] = Ka · (ck/cs).
[H⁺] = 4.9·10⁻¹⁰ · (0.05 M ÷ 0.015 M).
[H⁺] = 1.63·10⁻⁹ M.