SSCE HSC Chemistry Solution Equilibria: What is the molar solubility of

What is the molar solubility of iron(II) hydroxide? A - HSC - SSCE Chemistry - Question 19 - 2022 - Paper 1

Question 19

What is the molar solubility of iron(II) hydroxide? A. 2.3 x 10⁶ mol L⁻¹ B. 2.9 x 10⁶ mol L⁻¹ C. 3.7 x 10⁶ mol L⁻¹ D. 4.9 x 10⁹ mol L⁻¹

Worked Solution & Example Answer:What is the molar solubility of iron(II) hydroxide? A - HSC - SSCE Chemistry - Question 19 - 2022 - Paper 1

Step 1

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Answer

To determine the molar solubility of iron(II) hydroxide (Fe(OH)₂), we start with the dissolution equation:

$Fe(OH)_2 (s) \rightleftharpoons Fe^{2+} (aq) + 2OH^{-} (aq)$

Let the molar solubility of Fe(OH)₂ be represented by 's'. Thus, we have:

The solubility product constant (Ksp) for iron(II) hydroxide can be expressed as:

$K_{sp} = [Fe^{2+}][OH^{-}]^2 = s(2s)^2 = 4s^3$

We need the value of Ksp, which is typically around 4.87 x 10⁶ at 25°C. Therefore:

$4s^3 = 4.87 x 10^{-16}$

To find 's', we rearrange the equation:

$s^3 = \frac{4.87 x 10^{-16}}{4} = 1.2175 x 10^{-16}$

Now, taking the cube root:

$s = \sqrt[3]{1.2175 x 10^{-16}} \approx 2.3 x 10^{-6} mol L^{-1}$

Thus, the molar solubility of iron(II) hydroxide is approximately 2.3 x 10⁶ mol L⁻¹, corresponding to option A.