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Ch.17 - Aqueous Ionic Equilibrium
Chapter 17, Problem 102

A solution containing potassium bromide is mixed with one containing lead acetate to form a solution that is 0.013 M in KBr and 0.0035 M in Pb(C2H3O2)2. Does a precipitate form in the mixed solution? If so, identify the precipitate.

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Identify the possible reaction: When potassium bromide (KBr) and lead acetate (Pb(C_2H_3O_2)_2) are mixed, the possible reaction is the formation of lead bromide (PbBr_2) and potassium acetate (K(C_2H_3O_2)).
Write the balanced chemical equation: KBr + Pb(C_2H_3O_2)_2 \rightarrow PbBr_2 + 2K(C_2H_3O_2).
Determine the solubility product (K_sp) for PbBr_2: Look up the K_sp value for lead bromide (PbBr_2) in a solubility table.
Calculate the ion product (Q) for PbBr_2: Use the concentrations of Pb^{2+} and Br^- ions in the mixed solution to calculate Q. The concentration of Br^- is twice that of KBr, and the concentration of Pb^{2+} is the same as Pb(C_2H_3O_2)_2.
Compare Q with K_sp: If Q > K_sp, a precipitate of PbBr_2 will form. If Q < K_sp, no precipitate will form.

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Solubility Product Constant (Ksp)

The solubility product constant (Ksp) is a numerical value that represents the equilibrium between a solid and its ions in a saturated solution. It is specific to a particular compound at a given temperature. For a precipitate to form, the product of the concentrations of the ions in solution must exceed the Ksp value of the potential precipitate.
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Precipitation Reactions

Precipitation reactions occur when two soluble salts react in solution to form an insoluble compound, known as a precipitate. This process is driven by the formation of a solid that separates from the liquid phase, often indicated by a change in color or turbidity. Identifying the ions involved helps predict whether a precipitate will form.
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Ion Concentration and Reaction Quotient (Q)

The reaction quotient (Q) is calculated using the current concentrations of the ions in solution. By comparing Q to the Ksp of a potential precipitate, one can determine if a precipitate will form. If Q exceeds Ksp, a precipitate will form; if Q is less than Ksp, no precipitate will form.
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