I don't know how to start this problem. Someone can help me please.
One dm3 of a solution was prepared containing 0.0040 mole of Pb(NO3)2. The Ksp of PbCI2 for the existing conditions is 2.4 x 10^-4. From the list below, choose the smallest numbers of NH4CI that when added to this solution will cause PbCI2 to precipitate. (Assume no increase in volume).
a) 0.25 mole
b) 0.30 mole
c) 0.20 mole
d) 0.15 mole
To solve this problem, we need to determine the amount of NH4Cl required to cause the precipitation of PbCl2.
First, we need to write the balanced chemical equation for the reaction between Pb(NO3)2 and NH4Cl:
Pb(NO3)2 + 2 NH4Cl → PbCl2 + 2 NH4NO3
From the balanced equation, we can see that one mole of Pb(NO3)2 reacts with two moles of NH4Cl to produce one mole of PbCl2.
Given that there is 0.0040 mole of Pb(NO3)2 in the solution, we need to find out the amount of NH4Cl needed to react with this.
Using the stoichiometry of the balanced equation, we can calculate the moles of NH4Cl required:
0.0040 mole Pb(NO3)2 x (2 moles NH4Cl / 1 mole Pb(NO3)2) = 0.0080 mole NH4Cl
So, we need 0.0080 mole of NH4Cl to react with the Pb(NO3)2.
Now, we compare the amount of NH4Cl needed (0.0080 mole) with the choices given:
a) 0.25 mole
b) 0.30 mole
c) 0.20 mole
d) 0.15 mole
Among the choices, the smallest number that is greater than or equal to 0.0080 mole is 0.15 mole. Therefore, the answer is (d) 0.15 mole.