Question

Precipitation is the formation of an insoluble substance. For the equation

AB(s)⇌A+(aq)+B−(aq),

precipitation represents a shift to the left and the production of a solid. From Le Châtelier's principle, we know that when the product of the concentrations of A+ and B− gets above a certain level, the reaction will respond by shifting left to decrease the concentrations of A+ and B−. This critical level, Ksp, is a constant at a certain temperature. In this case,

Q=[A+][B−],

where Q is the ion product.When Q>Ksp, precipitation occurs until Q is equal to Ksp.

When Q≤Ksp, a precipitate does not form.

Question:

a) What is the value of Q when the solution contains 2.50×10−3M Mg2+ and 2.00×10−3M CO32−?

b) What concentration of the lead ion, Pb2+, must be exceeded to precipitate PbBr2  from a solution that is 1.00×10−2 M in the bromide ion, Br−? Ksp for lead(II) bromide is 4.67×10−6 .

Answer 1

2- Ma cos () Ma (aq) + Co (aa) CM22 Cco (2.50x 10-3) x (2.00 x lo3 2+ 1 5.00 X 10 b1f the poduet af the molan coneentroations of the Constituent ions ef the Salt in the Solution with Suitable powens ex eeeds the value af the Solubility Pwo duet (Ksp) of the Salt at that tempenatune, then the Salt will be pmeeipitated froom the Solution. If the Value ef tne produet fails to exeecd the SolubilityY Praduet of that Salt, then the Sat aill not be pneeipitated 2+ Ph (a) + 2 BY (ag) PbBr, (S) KSP ADG KSP Ph2 Br 4.67 x106 (I.00x 10-2)2 2+ 2t 0.0467 Coneentration of the leadion must be gmeaten than 0.0467 M to pme eipitate PbBn, .*. 2