Destroyer question

[kov82]

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Gen chem #98 The Ksp of PbCl2 is 1.6X10^-5 at 25 degrees C, what is the solubility of PbCl2, in .01 M KCl?

they say the answer is .16 M, I got that, but because the common ion was Cl- for the answer I multiplied my x which was .16 by two since Cl- is 2x, and that was one of the choices, how should I think of this question? is it simply since they didn't ask what is the solubility of Cl-? if they did, the answer would by .32M?

 

[iwannabadentist]

you would set it up as:
Ksp = [x] * [2x+.01]^2
But since 2x would be much smaller compared to .01, you can ignore it from the calculation. Then you would have:
1.6 x 10^-5 = [x] (.01)^2
x = (1.6 x 10^-5)/(1.0 x 10^-4)
x = 1.6 x 10^-1
x = .16 M

 

[kov82]

yea I got that, I know how to do it, but I thought it was a kind of "trick" considering 2 moles of Cl-, so I multiplied it with two, I'm guessing its wrong because it asked for solubility of the whole molecule, if it had said the concentration of Cl-, then it would be .32 right?