Fractional Precipitation Pogil Answer Key May 2026

Let’s assume a standard POGIL scenario: You have a solution containing 0.01 M Ag⁺, 0.01 M Pb²⁺, and 0.01 M Hg₂²⁺. You slowly add 0.1 M HCl (source of Cl⁻ ions). Relevant Ksp values:

Answer: Yes, but only within a specific window. A separation is "complete" when less than 0.1% of the first ion remains. fractional precipitation pogil answer key

POGIL Answer: To separate (Ag^+) from (Pb^2+): Let’s assume a standard POGIL scenario: You have

Question: Two salts have (K_sp) values of (A = 4.0 \times 10^-5) and (B = 2.0 \times 10^-15). You add a common anion dropwise. Which precipitates first? Answer: Salt B, because it has the smaller (K_sp). Exception: The salts must have the same stoichiometry (e.g., both (MX) or both (MX_2)). If not, you must calculate the required ([Anion]). Question: Two salts have (K_sp) values of (A = 4

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

Explanation: 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.

Answer: (AgCl) precipitates until the (Ag^+) concentration drops dramatically. During this time, (Pb^2+) remains in solution because the (Cl^-) concentration hasn't yet reached 0.041 M. Only when (Ag^+) is nearly gone does (PbCl_2) begin to form.