: The solution is supersaturated. Precipitation occurs until Kspcap K sub s p end-sub 3. Selective Precipitation
The fractional precipitation POGIL illustrates that the ion forming the salt with the cap K sub s p end-sub
Most POGIL exercises ask you to calculate the exact concentration of the added ion needed to start precipitation. To find this "answer key" moment, you use the Kspcap K sub s p end-sub expression:
For a visual explanation of how to calculate the concentration of remaining ions after the first precipitation, check out the Chapter 17 Fractional Precipitation lecture on YouTube. fractional precipitation pogil answer key
Fractional precipitation occurs when a reagent is added dropped-by-drop to a solution containing multiple dissolved ions. If the reagent can form an insoluble precipitate with more than one of these ions, the ions will not drop out of the solution at the same time. Instead, the compound with the lower solubility will precipitate first. Key Terms to Know
This allows you to calculate the percentage of separation efficiency. If more than 99.9% of the first ion has precipitated before the second begins, the separation is considered highly successful. Navigating the POGIL Activity
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[Precipitating Ion]=Ksp[Target Ion][Precipitating Ion] equals the fraction with numerator cap K sub s p end-sub and denominator [Target Ion] end-fraction Model 3: Determining Separation Efficiency
open bracket cap C cap O sub 3 raised to the 2 minus power close bracket equals the fraction with numerator cap K sub s p end-sub and denominator open bracket cap Z n raised to the 2 plus power close bracket end-fraction Step 3: Determining the Order of Precipitation
value always precipitates first. POGIL models will quickly show you that this is only true if the compounds have the same ion-to-cation ratio (e.g., both are 1:1 electrolytes like AgClcap A g cap C l AgBrcap A g cap B r To find this "answer key" moment, you use
[Ag+]=8.5×10-16 Mopen bracket Ag raised to the positive power close bracket equals 8.5 cross 10 to the negative 16 power M
AgCl(s)⇌Ag+(aq)+Cl−(aq)Ksp=[Ag+][Cl−]AgCl open paren s close paren is in equilibrium with Ag raised to the positive power open paren a q close paren plus Cl raised to the negative power open paren a q close paren space cap K sub s p end-sub equals open bracket Ag raised to the positive power close bracket open bracket Cl raised to the negative power close bracket
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