We’re being asked to **determine if a precipitate will form** by mixing 100.0 mL of 1.0 X 10 ^{-2} M Pb(NO_{3})_{2} and 100.0 mL of 1.0 X 10^{-3} M NaF.

For this, we need to **compare the reaction quotient (Q) vs. the solubility product constant (K _{sp})**.

Recall that when:

• Q > K_{sp}: the solution is supersaturated and *a precipitate will form*. Reactants are favored.

• Q = K_{sp}: the solution is at equilibrium and no precipitate will form.

• Q < K_{sp}: the solution is unsaturated and no precipitate will form. Products are favored.

The expected precipitate is PbF_{2}.

The dissociation of PbF_{2} in water is as follows:

PbF_{2}(s) ⇌ Pb^{2+}(aq) + 2 F^{–}(aq)

Step 1. Calculate the concentration of each

$\frac{\mathbf{1}\mathbf{.}\mathbf{0}\mathbf{\times}\mathbf{}{\mathbf{10}}^{\mathbf{-}\mathbf{2}}\mathbf{}\mathbf{mol}\mathbf{}{\mathbf{Pb}}^{\mathbf{2}\mathbf{+}}}{\mathbf{1}\mathbf{}\mathbf{L}}\mathbf{\times}\frac{\mathbf{100}\mathbf{}\overline{)\mathbf{mL}}}{\mathbf{200}\mathbf{}\mathbf{}\overline{)\mathbf{mL}}}\mathbf{=}\mathbf{}\mathbf{5}\mathbf{.}\mathbf{0}\mathbf{\times}\mathbf{}{\mathbf{10}}^{\mathbf{-}\mathbf{3}}\mathbf{}\mathbf{M}\mathbf{}\mathbf{}{\mathbf{Pb}}^{\mathbf{2}\mathbf{+}}\phantom{\rule{0ex}{0ex}}\frac{\mathbf{1}\mathbf{.}\mathbf{0}\mathbf{\times}\mathbf{}{\mathbf{10}}^{\mathbf{-}\mathbf{3}}\mathbf{}\mathbf{mol}\mathbf{}{\mathbf{F}}^{\mathbf{-}}}{\mathbf{1}\mathbf{}\mathbf{L}}\mathbf{\times}\frac{\mathbf{100}\mathbf{}\overline{)\mathbf{mL}}}{\mathbf{200}\mathbf{}\mathbf{}\overline{)\mathbf{mL}}}\mathbf{=}\mathbf{}\mathbf{5}\mathbf{.}\mathbf{0}\mathbf{\times}\mathbf{}{\mathbf{10}}^{\mathbf{-}\mathbf{4}}\mathbf{}\mathbf{M}\mathbf{}\mathbf{}{\mathbf{F}}^{\mathbf{-}}\mathbf{}$

A solution is prepared by mixing 100.0 mL of 1.0 X 10 ^{-2} M Pb(NO_{3})_{2} and 100.0 mL of 1.0 X 10^{-3} M NaF. Will PbF_{2}(s) (K_{sp} = 4 X 10 ^{-8}) precipitate?

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Selective Precipitation concept. If you need more Selective Precipitation practice, you can also practice Selective Precipitation practice problems.

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Based on our data, we think this problem is relevant for Professor Du's class at UGA.

What textbook is this problem found in?

Our data indicates that this problem or a close variation was asked in Chemistry: An Atoms First Approach - Zumdahl Atoms 1st 2nd Edition. You can also practice Chemistry: An Atoms First Approach - Zumdahl Atoms 1st 2nd Edition practice problems.