Fractional Precipitation Pogil Answer Key -

Pay attention to the stoichiometry. If one salt is XYcap X cap Y and the other is X2Ycap X sub 2 cap Y , you cannot compare Kspcap K sub s p end-sub

(or other precipitating ion) required for the second salt and plug it back into the Kspcap K sub s p end-sub expression of the first salt. Why You Shouldn't Just Copy the Answer Key

values or concentrations you're dealing with, and we can walk through the calculation together! fractional precipitation pogil answer key

If you know the concentration of the ion already in the beaker, you solve for the concentration of the ion you are adding. Precipitation begins the moment the exceeds the Kspcap K sub s p end-sub . 3. Determining Which Ion Precipitates First A classic POGIL question might look like this: "A solution contains 0.10 M Cl−cap C l raised to the negative power and 0.10 M Br−cap B r raised to the negative power Ag+cap A g raised to the positive power is added, which silver salt forms first?" Step 1: Look up Kspcap K sub s p end-sub AgClcap A g cap C l AgBrcap A g cap B r Step 2: Calculate the needed to precipitate each. Answer: Since AgBrcap A g cap B r has a much lower Kspcap K sub s p end-sub

POGILs are notorious for being picky about sig figs. Ensure your calculations match the precision of the data given in the "Model" diagrams. Pay attention to the stoichiometry

Instead of searching for a "cheat sheet," focus on the relationship between , the "snowstorm" starts.

value tells you how much of a salt can dissolve before the solution becomes saturated. The salt is very insoluble (precipitates easily). Large Kspcap K sub s p end-sub : The salt is more soluble. The Rule of Thumb: If you have two ions (like Cl−cap C l raised to the negative power I−cap I raised to the negative power ) and you start adding a common precipitating agent (like AgNO3cap A g cap N cap O sub 3 ), the salt with the lowest Kspcap K sub s p end-sub will generally precipitate first. 2. Calculating the "Trigger" Concentration If you know the concentration of the ion

values directly; you must calculate the required concentration of the common ion for each.