When adding the 25 mL of DI water to your saturated solution of calcium hydroxid

Question

When adding the 25 mL of DI water to your saturated solution of calcium hydroxide, you are changing the ion concentration. Why does this not matter? Saturated solutions of barium hydroxide are prepared at two different temperatures, equilibrated, filtered, and then 15.00 mL portions of the solution are titrated with 0.180 M hydrochloric acid: What are the values of K_sp and delta G^degree at each temperature and what are the values of delta H^degree and delta S^degree for the dissociation of barium hydroxide?

Explanation / Answer

4. Adding 25 ml DI water to Ca(OH)2 does not matter as Ca(OH)2 is a strong electrolyte and disscociate comletely into its ions at all concentrations.

5. Ba(OH)2 at 25 oC

molarity of Ba(OH)2 solution = 0.180 M x 17 ml/15 ml = 0.204 M

Ksp = 0.204

dG = -RTlnK

      = -8.314 x 298 ln(0.204) = 3938.44 kJ

Ba(OH)2 at 65 oC

molarity of Ba(OH)2 solution = 0.180 M x 55 ml/15 ml = 0.660 M

Ksp = 0.660

dG = -RTlnKsp

      = -8.314 x 338 ln(0.660) = 1167.65 kJ

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