Since the compounds are ionic compounds, they form ions when dissociating in water. The dissociation of PbBr2 and Pb(NO3)2 in water are as follows:
The bromide ion, Br–, has a charge of – 1. This means Pb has a charge of +2:
PbBr2(s) ⇌ Pb2+(aq) + 2 Br–(aq)
The nitrate ion, NO3–, has a charge of – 1. This means Pb has a charge of +2:
Pb(NO3)2(s) → Pb2+(aq) + 2 NO3–(aq)
Notice that there is a common ion present, Pb2+. The common ion effect states that the solubility of a salt is lower in the presence of a common ion.
We can construct an ICE table for the dissociation of PbBr2. Remember that solids are ignored in the ICE table.
The Ksp of PbBr2 is 6.60 x 10-6
What is the molar solubility(M) of PbBr2 in a 0.500M Pb(NO3)2 solution?
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