[ [I^-] = \fracK_sp(\textAgI)[Ag^+] = \frac8.5 \times 10^-171.8 \times 10^-8 = 4.7 \times 10^-9 , M ]
For AgI: (K_sp = [Ag^+][I^-] \Rightarrow [Ag^+] = \fracK_sp[I^-] = \frac8.5 \times 10^-170.010 = 8.5 \times 10^-15 , M)
This calculation demonstrates why fractional precipitation works. The first ion (I⁻) is reduced to a negligible level before the second ion (Cl⁻) begins to react. Learning Objective 3: Common Mistakes and Misconceptions POGIL activities often include metacognitive questions. Here’s how a high-quality answer key addresses frequent errors. fractional precipitation pogil answer key best
For PbCrO₄ (1:1 salt): [ [Pb^2+] = \frac2.8 \times 10^-130.050 = 5.6 \times 10^-12 M ]
The salt with the smaller (K_sp) requires a lower concentration of the common ion to reach saturation. This is the cardinal rule of fractional precipitation. Learning Objective 2: Calculating Ion Concentration at the Second Precipitation Point Question: As you continue adding AgNO₃, AgI continues to precipitate. At the moment just before AgCl begins to precipitate, what is the concentration of I⁻ remaining in solution? [ [I^-] = \fracK_sp(\textAgI)[Ag^+] = \frac8
Let’s work through that logic—because this exact calculation appears in every quality answer key. What follows is a model answer key for the most common POGIL on this topic. I’ve organized it into learning objectives, key questions, and the reasoning behind each correct answer. Learning Objective 1: Predicting the Order of Precipitation Question: A solution contains 0.010 M Cl⁻ and 0.010 M I⁻. Solid AgNO₃ is added dropwise. Using the (K_sp) values below, calculate the [Ag⁺] required to begin precipitation of each salt. Which precipitates first?
| Salt | (K_sp) | |------|------------| | AgCl | (1.8 \times 10^-10) | | AgI | (8.5 \times 10^-17) | Here’s how a high-quality answer key addresses frequent
Now, go separate those ions with confidence.