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

Question

Taya2010

11 days 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:

Anarel [2.9K] · Answer 1 · 2026-04-11T03:59:31+03:00

Answer:

9.88

Explanation:

The higher the Ksp, the more soluble a compound is. Hence, Co(OH)₂ ranks as the least soluble hydroxide.

Its maximum concentration must be 1x10⁻⁶ M, and the reaction can be represented as:

Co(OH)₂(s) ⇄ Co⁺²(aq) + 2OH⁻(aq)

Thus, [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

lions [2.9K] · Answer 2 · 2026-04-11T03:59:25+03:00

Co(OH)₂ can be effectively isolated from Ca(OH)₂ at pH: 9.885

Further explanation

Solubility represents the highest potential amount of a substance that can dissolve in solvents.

Ksp signifies the ion product at equilibrium.

Solubility (s) and solubility constants (Ksp) pertaining to the AxBa solution can be expressed as follows.

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

s as bs

Ksp = [Aᵃ⁺]ᵃ [Bᵇ⁻]ᵇ

Ksp = (as)ᵃ (bs)ᵇ

Solubility units are expressed as mol/liter or grams/liter.

Ksp represents the product of ions in a saturated state of equilibrium.

Qsp denotes the product of ions from the reacting substance.

When Qsp <Ksp, sediment has not yet occurred.

When Qsp = Ksp, a saturated solution is reached, whereprecipitation occurs.

Conversely, when Qsp> Ksp, a sediment solution forms.

The lesser the solubility of a substance, the more challenging it is to dissolve, correlating with a lower Ksp value. Conversely, a larger Ksp denotes greater solubility, allowing easier dissolution.

Considering the two hydroxy solutions, Co(OH)₂ has a lower Ksp value, thus precipitating first, making it separable from the Ca(OH)₂ solution.

Given that the Co concentration is 1 × 10−6 M, we can determine pH at which Co(OH)₂ precipitates

Co(OH)₂ --> Co²⁺ + 2OH⁻

Ksp Co(OH)₂= [Co²⁺][OH⁻]²

5.9.10⁻¹⁵ = 1.10⁻⁶[OH⁻]²

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

$[OH^-]=7.68.10^{-5}$

$\displaystyle pOH=-log~7.68.10^{-5}\\\\pOH=4.114\\\\pH=14-4.114=\boxed{\bold{9.885}}$

Learn more

Factors affecting solubility and dissolution rate

The solubility of a substance

Keywords: solubility, Ksp, precipitated, less soluble hydroxide, Co(OH)₂,Ca(OH)₂