Question

The salts X(NO₃)₂ and Y(NO₃)₂ (where X⁺ and Y⁺ are metal ions) are dissolved in water to give a solution which is 0.1 M in each of them. Using the K_sp values listed below, decide which aqueous reagent, if any, will definitely precipitate X⁺ before precipitating Y⁺ from solution.

Given K_sp values:

XCl2, 1x10^-5 YCl₂, 1x10^-10 X(OH)₂, 1x10^-10 Y(OH)₂, 1x10^-5

A)1M NH3

B)1M HCl

C)1M HNO3

D) 1M NaCl

E) None of the above reagents will accomplish the precipitation

Answer 1

From the given Ksp's, Ksp of XCl2 and YCl2 are very different, so Cl-(chloride) appears a good choice for their separation.

Ksp for XCl2 = 1*10^-5 and ksp for YCl2 = 1*10^-10

Ksp of YCl2 is smaller and lower Ksp indicates lower solubility. Thus, YCl2 will form a precipitate first as [Cl-] increases. But we want to precipate X+ before precipitating Y+, so chloride will not be a good choice for our purpose.

Another choice is hydroxide ions. Ksp values show that it will be good choice for reagent. As the ksp value for X(OH)2 is lower. This indicates lower solubility and hence X(OH)2 will precipitate first.

Among the given reagents, no reagent provides for hydroxide ions. So none of the given reagents will accomplish the precipitation.

Therefore, the answer is E.