Fractional Precipitation Pogil Answer Key Hot! Jun 2026

Fractional precipitation, also known as selective precipitation , is a technique that exploits differences in ion solubility to separate them. By adding a reagent that forms an insoluble salt with specific target ions, and carefully controlling the concentration of that precipitant, it’s possible to remove the ions from the solution in a step-by-step, or fractional, manner.

Hg₂Cl₂ has the smallest Ksp (1.3 × 10⁻¹⁸), so it will precipitate first.

A solution contains ( \textBa^2+ ) and ( \textSr^2+ ), each at 0.10 M. You add ( \textNa_2\textSO 4 ) dropwise. (K sp(\textBaSO 4) = 1.1 \times 10^-10) (K sp(\textSrSO_4) = 3.2 \times 10^-7)

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 fractional precipitation pogil answer key

If you are working on a specific problem from your worksheet, let me know:

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

For salts with the same ion ratio (1:1 like AgCl and Hg₂Cl₂), the smallest Ksp means the lowest solubility. However, careful: Hg₂Cl₂ is actually Hg₂²⁺ + 2Cl⁻ → Hg₂Cl₂. You must calculate the [Cl⁻] needed to start precipitation. A solution contains ( \textBa^2+ ) and (

5.0×10-13=(1.8×10-9)×[Br−]5.0 cross 10 to the negative 13 power equals open paren 1.8 cross 10 to the negative 9 power close paren cross open bracket cap B r raised to the negative power close bracket

Ksp=[Ag+][Cl−]cap K sub s p end-sub equals open bracket cap A g raised to the positive power close bracket open bracket cap C l raised to the negative power close bracket

Hg₂Cl₂ and possibly some AgCl precipitate, but PbCl₂ remains dissolved. POGIL models will quickly show you that this

Understanding Fractional Precipitation in Chemistry Fractional precipitation is a powerful laboratory technique used to separate a mixture of ions in a solution by adding a reagent that forms a precipitate with each ion at different concentrations. By carefully controlling the concentration of the precipitating agent, chemists can selectively remove one ion at a time based on the solubility product constant ( Kspcap K sub s p end-sub ) of the resulting compounds.

A typical problem involves a solution containing two anions, such as Chloride ( Cl−Cl raised to the negative power ) and Chromate ( CrO42−CrO sub 4 raised to the 2 minus power ), to which a cation like Silver ( Ag+Ag raised to the positive power ) is slowly added.

Remember that the "first" precipitate is the one that reaches its Ksp limit at the lowest added reagent concentration.