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A lab technician adds 0.135 mol of KOH to 1.00 L of 0.0010 M Ca(NO 3 ) 2 . K sp

ID: 967189 • Letter: A

Question

A lab technician adds 0.135 mol of KOH to 1.00 L of 0.0010 M Ca(NO3)2. Ksp = 6.5 × 10–6 for Ca(OH)2. Which of the following statements is correct?

Calcium hydroxide precipitates until the solution is saturated.

The solution is unsaturated and no precipitate forms.

The concentration of calcium ions is increased by the addition of the hydroxide ions.

One must know Ksp for calcium nitrate to make meaningful predictions on this system.

The presence of KOH will raise the solubility of Ca(NO3)2.

Calcium hydroxide precipitates until the solution is saturated.

The solution is unsaturated and no precipitate forms.

The concentration of calcium ions is increased by the addition of the hydroxide ions.

One must know Ksp for calcium nitrate to make meaningful predictions on this system.

The presence of KOH will raise the solubility of Ca(NO3)2.

Explanation / Answer

Q = [Ca+2][OH-]^2

mmol of Ca = 0.001

mmol of OH- = 0.135

Q = [Ca+2][OH-]^2 = (0.001)(0.135^2) = 0.00001822 = 1.8*10^-5

since

Q >> K, expect precipitaiton

Calcium hydroxide precipitates until the solution is saturated.

Calcium hydroxide precipitates until the solution is saturated.

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