Determine [Zn^2+], [CN^-), and [HCN) in a saturated solution of Zn(CN)2 with a f

Question

Determine [Zn^2+], [CN^-), and [HCN) in a saturated solution of Zn(CN)2 with a fixed pH of 4.000. The Ksp for Zn(CN)2 is 3.0 x 10^-16. The Ka for HCN is 6.2 x 10^-10. [Zn^2+] = Number M [HCN] = Number M [CN^-] = Number M Find the concentration of Hg2^2+ in 0.0010 M KI saturated with Hg2I2. Include activity coefficients in your solubility-product expression. The Ksp of Hg2I2 is 4.6x 10^-29. [Hg^2+ 2] = Number M What is the activity coefficient of H^+ in a solution containing 0.040 M HCI and 0.020 M Ca(CIO4)2? Number What is the pH of this solution? Number

Explanation / Answer

1.

As ph is given to be constant = 4

[H+] is constant and is equal to 10-4--------------- 1

Ka of HCN = [H][CN] = 6.2 *10-10----------------------- 2

Thus from 1 and 2 [CN] = 6.2 * 10-6 --------- 3

Ksp of Zn(CN)2 = [Zn][CN]2 = 3 * 10-16 ----------4

From 3 and 4 [Zn] = 8.324 * 10-6

2.

Hg2I2 ------> Hg22+ + 2I-

Thus Ksp = [Hg2][I]2 = 4.6 *10-29

[I] = 10-3M

Thus [Hg22+] = 4.6 * 10-23 (From Ksp formula)

3.

2HCl + Ca(ClO4)2 -----> CaCl2 + 2HClO4

Concentration of HClO4 = 0.04M

HClO4 is a strong acid dissociates completely

HClO4 -----> H+ + ClO4-

Conc of H+ = 0.04M

Therefore Ph = 2 - log4

Ph = 1.398

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