Most POGIL worksheets on this topic guide you through a specific scenario: a beaker contains two different anions (like Cl−cap C l raised to the negative power CrO42−cap C r cap O sub 4 raised to the 2 minus power ), and a cation (like Ag+cap A g raised to the positive power
The method relies on the . The ion with the smallest Kₛₚ for the precipitating ion is the one that will precipitate first. As one ion is removed, the concentration of the remaining target ion continues to increase, eventually causing the next salt to precipitate.
Ksp = [Ag⁺][Cl⁻] = 1.8 × 10⁻¹⁰ [Cl⁻] = (1.8×10⁻¹⁰) / (0.01) = 1.8 × 10⁻⁸ M
values. For example, in a common POGIL model involving Zinc and Copper(II) ions: Zinc Carbonate ( cap Z n cap C cap O sub 3 Copper(II) Carbonate ( cap C u cap C cap O sub 3 cap K sub s p end-sub is typically different (e.g., The salt with the cap K sub s p end-sub fractional precipitation pogil answer key
Here is how to determine which compound precipitates first and calculate the remaining concentration of the first ion. Step 1: Write out the Equilibrium Expressions
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
: Precipitation begins the moment the Reaction Quotient ( Qspcap Q sub s p end-sub ) exceeds the Kspcap K sub s p end-sub for that specific compound. 2. Identifying the "Precipitation Window" 15.2 Predicting Precipitation – General Chemistry 3e Most POGIL worksheets on this topic guide you
"The range of ([Cl^-]) for successful separation is from (1.8\times10^-8 M) (start AgCl) to (0.041 M) (start PbCl_2)."
Looking for more POGIL answer keys or chemistry study guides? Check out our other articles on solubility equilibrium, common ion effect, and acid-base titration POGILs.
Fractional precipitation is a laboratory technique used to separate ions in a solution by adding a reagent that forms a precipitate with one or more of those ions. Because different salts have different solubilities (represented by the solubility product constant, ), they don't all precipitate at the same time. Ksp = [Ag⁺][Cl⁻] = 1
The or wording that is causing confusion
precipitates first because it requires a much lower concentration of iodide.
Ag2CrO4(s)⇌2Ag+(aq)+CrO42−(aq)Ksp=[Ag+]2[CrO42−]Ag sub 2 CrO sub 4 open paren s close paren is in equilibrium with 2 Ag raised to the positive power open paren a q close paren plus CrO sub 4 raised to the 2 minus 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 squared open bracket CrO sub 4 raised to the 2 minus power close bracket
represents the equilibrium constant for a solid substance dissolving in an aqueous solution. It is a measure of the extent to which a compound can dissolve.For a general dissolution equation: