AAMC 6 QUESTION 63: Solubility

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harro

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The passage says: The student determines the molar solubility, S, of PbI2(s) in water to be 1.89*10^-3. In a similar experiment the student determines the Ksp of lead(II)bromide to be 4.6*10^-6.

Question: How many grams of lead(II)iodide are present in 100mL of a saturated aqueous solution?
A. 0.0410g
B. 0.0871g
C. 2.470g
D. 8.71g
The answer was B because 100mL=0.1L and 0.1L*1.89*10^-3*461g/mol=0.09g

My question is... I thought solubility was supposed to be something like [I-]? Because
PbI2--->Pb+2I-. How can S represent PbI2? Shouldn't it represent [I-]? (and on a side note how do you know if S represents [Pb2+] or [I-]?)
 
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