Magnesium hydroxide, Mg(OH)2, found in milk of magnesia, has a solubility of 7.05 × 10-3 g L-1 at 25 °C. Calculate Ksp for Mg(OH)2.
To calculate the value of Ksp (solubility product constant) for Mg(OH)2, we need to use the given solubility and the balanced chemical equation for its dissolution.
The balanced chemical equation for the dissolution of Mg(OH)2 is:
Mg(OH)2(s) ⇌ Mg2+(aq) + 2OH-(aq)
From this equation, we can see that 1 mole of Mg(OH)2 produces 1 mole of Mg2+ and 2 moles of OH-. Therefore, the solubility of Mg(OH)2 can be expressed as [Mg2+] × [OH-]².
Given that the solubility of Mg(OH)2 is 7.05 × 10^-3 g/L, we need to convert it to moles per liter. First, calculate the molar mass of Mg(OH)2:
Molar mass of Mg(OH)2 = (24.31 g/mol for Mg) + (2 × 16.00 g/mol for O) + (2 × 1.01 g/mol for H)
= 58.33 g/mol
Now, convert the solubility to moles per liter:
Solubility of Mg(OH)2 = (7.05 × 10^-3 g/L) / (58.33 g/mol)
≈ 1.21 × 10^-4 mol/L
Using the balanced chemical equation, we know that 1 mole of Mg(OH)2 produces 1 mole of Mg2+ and 2 moles of OH-. Therefore, we have:
[Mg2+] = 1.21 × 10^-4 mol/L
[OH-] = 2 × (1.21 × 10^-4 mol/L) = 2.42 × 10^-4 mol/L
Now, we can calculate the value of Ksp using the expression [Mg2+] × [OH-]²:
Ksp = [Mg2+] × [OH-]²
= (1.21 × 10^-4 mol/L) × (2.42 × 10^-4 mol/L)²
≈ 7.48 × 10^-12
Therefore, the solubility product constant (Ksp) for Mg(OH)2 is approximately 7.48 × 10^-12.
Ksp= 4x^3 x=solubility so plug it in
AX Ksp=X^2
AX3 = 27x4
A2X3 = 108x5
just know these 4