Question

In: Chemistry

HClO / KClO buffer system is to be constructed that is also 0.043 M in Zn2+....

HClO / KClO buffer system is to be constructed that is also 0.043 M in Zn²⁺.

What is the minimum [HClO] / [ClO^-] that must be maintained to keep a precipitate of zinc hydroxide from forming?

Expert Solution

[Zn2+] = 0.043 M

Zn+2 + 2OH- Zn(OH)2(s)

Ksp of Zn(OH)2 = 5 x 10^-17

Ksp = [Zn2+][OH-]^2

5 x 10^-17 = 0.043 * [OH-]^2

[OH-] = 3.41 x 10^-8 M

Hence this is the minimum concentration of OH- that is required to precipitate Zn(OH)2.

pOH = - log (3.41 x 10^-8)

= 7.46

pH = 14 - 7.46

= 6.54

Hence, 6.54 is the maximum pH that will precipitate Zn(OH)2.

For a buffer system we have:

pH = pKa + log [ClO-] / [HClO]

6.54 = 7.53 + log [ClO-] / [HClO]

log [ClO-] / [HClO] = - 0.99

[ClO-] / [HClO] = 0.1023

[HClO] / [ClO-] = 1 / 0.1023

[HClO] / [ClO-] = 9.77

Hence, [HClO] / [ClO-] = 9.77 is the minimum value that must be maintained to keep a precipitate of zinc hydroxide from forming.

queen_honey_blossom answered 2 years ago

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