A mineral sample is analyzed for its cobalt and calcium content. A sample is dissolved, and then the cobalt and calcium are prec

Question

3 years ago

14

A mineral sample is analyzed for its cobalt and calcium content. A sample is dissolved, and then the cobalt and calcium are prec

ipitated as Co(OH)2(s) and Ca(OH)2(s) . At what pH can Co(OH)2(s) be separated from Ca(OH)2(s) at 25 °C? Assume that an effective separation requires a maximum concentration of the less soluble hydroxide of 1×10−6 M . Ksp[Co(OH)2]=5.9×10−15 M3 Ksp[Ca(OH)2]=5.0×10−6 M3

Chemistry

2 answers:

bekas [8.4K] · Answer 1 · 2022-05-17T07:50:43+03:00

Answer:

9.88

Explanation:

As higher is the Ksp, more soluble is the compound. So, Co(OH)₂ is the less soluble hydroxide.

The maximum concentration of it must be 1x10⁻⁶ M, and the reaction is:

Co(OH)₂(s) ⇄ Co⁺²(aq) + 2OH⁻(aq)

So, [Co⁺²] = 1x10⁻⁶M

Ksp = [Co⁺²] *[OH⁻]²

[OH⁻]² = 5.9x10⁻¹⁵/1x10⁻⁶

[OH⁻] = √(5.9x10⁻⁹)

[OH⁻] = 7.6811x10⁻⁵

pOH = -log[OH⁻]

pOH = -log(7.6811x10⁻⁵)

pOH = 4.11

Knowing that pH + pOH = 14

pH = 14 - 4.11

pH = 9.88

Contact [7] · Answer 2 · 2022-05-17T08:53:22+03:00

Co(OH)₂ can be separeted from Ca(OH)₂ at <u>pH : 9.885</u>

<h3>Further explanation </h3>

Solubility is the maximum amount of a substance that can dissolve in some solvents.

Ksp is an ion product in equilibrium

Solubility (s) and solubility constants (Ksp) of the AxBa solution can be stated as follows.

AₓBₐ (s) ← ⎯⎯⎯⎯ → aAᵃ⁺ (aq) + b Bᵇ⁻ (aq)

s as bs

Ksp = [Aᵃ⁺]ᵃ [Bᵇ⁻]ᵇ

Ksp = (as)ᵃ (bs)ᵇ

Solubility units in the form of mol / liter or gram / liter

Ksp is the product of ions in an equilibrium saturated state

Qsp is the product of the ion ions from the reacting substance

Qsp <Ksp = solution has not occurred sediment

Qsp = Ksp = saturated solution, exactly the precipitate will occur

Qsp> Ksp = sediment solution

The smaller the solubility of a substance, the more difficult it is to dissolve, the smaller the Ksp value. The greater the Ksp, the greater the solubility so that it can dissolve more easily

From the 2 hydroxide solutions above, Co(OH)₂ has a smaller Ksp value, so that a precipitate will form first so that it can be separated from the Ca(OH)₂ solution

Because the Co concentration is 1 × 10−6 M, we determine the pH when Co(OH)₂ precipitated

Co(OH)₂ --> Co²⁺ +2OH⁻

Ksp Co (OH)₂= [Co²⁺][OH⁻]²

5.9.10⁻¹⁵ = 1.10⁻⁶[OH⁻]²

$\displaystyle [OH^-]^2=\frac{5.9.10^{-15}}{1.10^{-6}}$