Calcium Buffer
Calculate the molar solubility of calcium hydroxide in buffer in each of the following pH:?
pH 5 pH 7 pH 8
Calcium hydroxide dissolves and dissociates according to: Ca (OH) ₂ (s) ⇄ Ca ² ⁺ (aq) + 2 OH ⁻ (aq) So the ion molarities a saturated solution satisfies the following balance equation Ksp = [Ca ⁺ ²] ∙ [OH ⁻] ² The solubility constant at 25 ° C [1] Ksp = 5.02 × 10 ^ -6 s is the molar solubility of Ca (OH) ₂. When dissolved s moles per liter, all the salt dissolves and dissociates, forming a salt of calcium ions molecule. Hence the molarities of calcium ions is: [Ca ² ⁺] = s The hydroxide ion concentration does not change due to buffering. That is attached to a level that is determined by the particular pH [OH ⁻] = 10 ^ (pH – 14) Thus Kn = s ∙ (10 ^ (pH – 14)) ² = s ∙ 10 ^ (2 ∙ pH – 28) => s = Ksp / 10 ^ (2 ∙ pH – 28) = Kn ∙ 10 ^ (28 to 2 ∙ pH) at pH = 5 s = 5.02 × 10 ^ -6 ∙ 10 ^ (28 — 2 ∙ 5) = 5.02 × 10 ^ -6 ∙ 10 ^ (18) = 5.02 × 10 ^ 12 mol / L at pH = 7 s = 5.02 × 10 ^ -6 ∙ 10 ^ (28 to 2 ∙ 7) = 5.02 × 10 ^ -6 ∙ 10 ^ (14) = 5.02 × 10 ^ 8 mol / L at pH = 8 s = 5.02 × 10 ^ -6 ∙ 10 ^ (28 to 2 ∙ 7) = 5.02 × 10 ^ -6 ∙ 10 ^ (12 ) = 5.02 × 10 ^ 6 mol / L
Alkaline Minerals – Alkalizing Supplement to Buffer & Neutralize Acids
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