Open Question
(a) Will Ca(OH)2 precipitate from solution if the pH of a 0.050 M solution of CaCl2 is adjusted to 8.0? (b) Will Ag2SO4 precipitate when 100 mL of 0.050 M AgNO3 is mixed with 10 mL of 5.0 * 10^-2 M Na2SO4 solution?
Ch.17 - Additional Aspects of Aqueous Equilibria
Chapter 17, Problem 73
A solution contains 2.0 * 10^-4 M Ag^+ (aq) and 1.5 * 10^-3 M Pb^2+ (aq). If NaI is added, will AgI (Ksp = 8.3 * 10^-17) or PbI2 (Ksp = 7.9 * 10^-9) precipitate first? Specify the concentration of I^- (aq) needed to begin precipitation.
Verified step by step guidance1
Step 1: Identify the relevant solubility product constants (Ksp) for AgI and PbI2. AgI has a Ksp of 8.3 \times 10^{-17}, and PbI2 has a Ksp of 7.9 \times 10^{-9}.
Step 2: Write the equilibrium expressions for the precipitation reactions. For AgI, the reaction is Ag^+ + I^- \rightleftharpoons AgI(s), and the Ksp expression is Ksp_{AgI} = [Ag^+][I^-]. For PbI2, the reaction is Pb^{2+} + 2I^- \rightleftharpoons PbI2(s), and the Ksp expression is Ksp_{PbI2} = [Pb^{2+}][I^-]^2.
Step 3: Calculate the concentration of I^- needed to begin precipitation for each compound. For AgI, rearrange the Ksp expression to find [I^-] = \frac{Ksp_{AgI}}{[Ag^+]}. For PbI2, rearrange the Ksp expression to find [I^-] = \sqrt{\frac{Ksp_{PbI2}}{[Pb^{2+}]}}.
Step 4: Substitute the given concentrations of Ag^+ and Pb^{2+} into the respective equations. Use [Ag^+] = 2.0 \times 10^{-4} M and [Pb^{2+}] = 1.5 \times 10^{-3} M to find the required [I^-] for each compound.
Step 5: Compare the calculated [I^-] values for AgI and PbI2. The compound with the lower [I^-] value will precipitate first, as it requires a lower concentration of I^- to reach its Ksp.
Related Practice
Textbook Question
Calculate the minimum pH needed to precipitate Mn1OH22 so completely that the concentration of Mn2 +1aq2 is less than 1 mg per liter [1 part per billion (ppb)].
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Textbook Question
Suppose that a 10-mL sample of a solution is to be tested for I- ion by addition of 1 drop (0.2 mL) of 0.10 M Pb1NO322. What is the minimum number of grams of I- that must be present for PbI21s2 to form?
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Textbook Question
A solution of Na2SO4 is added dropwise to a solution that is 0.010 M in Ba2+(aq) and 0.010 M in Sr2+(aq). (a) What concentration of SO42- is necessary to begin precipitation? (Neglect volume changes. BaSO4: Ksp = 1.1⨉10-10; SrSO4: Ksp = 3.2⨉10-7.)
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Textbook Question
A solution of Na2SO4 is added dropwise to a solution that is 0.010 M in Ba2+(aq) and 0.010 M in Sr2+(aq). (b) Which cation precipitates first?
616
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Textbook Question
A solution of Na2SO4 is added dropwise to a solution that is 0.010 M in Ba2+(aq) and 0.010 M in Sr2+(aq). (c) What is the concentration of SO42-(aq) when the second cation begins to precipitate?
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