Pogil Answer Key [top] | Fractional Precipitation

The Art of Separation: Unlocking the ‘Fractional Precipitation’ POGIL Answer Key

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• Precipitation order: Lowest Ksp → highest Ksp (for same salt type).
• Key calculation: [precipitating ion] = Ksp / [metal ion]^(1/n).
• Separation feasibility: Requires >10³ difference in Ksp.
• Common POGIL answer: Hg₂²⁺ precipitates first; Pb²⁺ last.

Step 2 — Compute critical precipitant concentration for each cation: fractional precipitation pogil answer key

Step 2 – Can they be separated?
Find ([Cl^-]) when ([Ag^+] = 1.0\times 10^-5) M (complete precipitation):
[ [Cl^-] = \fracK_sp(AgCl)[Ag^+]\textfinal = \frac1.8\times 10^-101.0\times 10^-5 = 1.8\times 10^-5 \text M ]
At this ([Cl^-]), check if (PbCl_2) has started:
(Q = [Pb^2+][Cl^-]^2 = (0.10)(1.8\times 10^-5)^2 = 3.24\times 10^-11)
Compare to (Ksp(PbCl_2) = 1.7\times 10^-5).
(Q \ll K_sp), so (Pb^2+) is still in solution. Separation is possible. Precipitation order: Lowest Ksp → highest Ksp (for

Fractional (or selective) precipitation is a technique used to separate multiple ions in a solution by adding a reagent that causes them to precipitate sequentially. Step 2 — Compute critical precipitant concentration for

Mistake #2: Forgetting to account for side reactions.

POGIL Insight: In reality, adding (Cl^-) to (Pb^2+) forms soluble complexes like (PbCl_3^-) at high ([Cl^-]). This is why in qualitative analysis, we add cold HCl specifically for (Pb^2+)—heat and excess (Cl^-) redissolve (PbCl_2).