Kidney stones are caused by the precipitation of either calcium oxalate, Ca(C2O4), or calcium phosphate, Ca3(PO4)2, in the kidneys. If the normal concentration of Ca2+ in the kidneys is 2.5 mM, at what concentration of oxalate ion will kidney stones begin to form?

1.1 × 10⁻⁶ M

Explanation:

Step 1: Given and required data

Step 2: Write the balanced equation for the solution reaction of calcium oxalate

CaC₂O₄(s) ⇄ Ca²⁺(aq) + C₂O₄²⁻(aq)

Step 3: Calculate the concentration of the oxalate ion to begin the precipitation of calcium oxalate

We will use the Ksp of calcium oxalate.

Ksp = 2.7 × 10⁻⁹ = [Ca²⁺].[C₂O₄²⁻]

[C₂O₄²⁻] = Ksp / [Ca²⁺]

[C₂O₄²⁻] = 2.7 × 10⁻⁹ / 2.5 × 10⁻³

[C₂O₄²⁻] = 1.1 × 10⁻⁶ M

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