---
title: "A student mixes \\(25.0\\ \\text{mL}\\) of \\(0.0800\\ \\text{M}\\ \\text{KI(aq)}\\) with \\(25.0\\ \\text{mL}\\) of \\(\\text{Pb}(\\text{NO}_3)_2\\text{(aq)}\\). The particulate representations show the ions before mixing and after \\(\\text{PbI}_2\\text{(s)}\\) forms. Every individual ion symbol represents the same amount of substance, and the same scale is used in both representations. Assume that the volumes are additive and that precipitation is complete.  Which choice correctly identifies the limiting reactant and the molar concentration of the excess reactant ion in the final mixture?"
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url: "https://nerd-notes.com/ubq/120114/"
date_modified: "2026-08-21T08:41:42+00:00"
---

# A student mixes \(25.0\ \text{mL}\) of \(0.0800\ \text{M}\ \text{KI(aq)}\) with \(25.0\ \text{mL}\) of \(\text{Pb}(\text{NO}_3)_2\text{(aq)}\). The particulate representations show the ions before mixing and after \(\text{PbI}_2\text{(s)}\) forms. Every individual ion symbol represents the same amount of substance, and the same scale is used in both representations. Assume that the volumes are additive and that precipitation is complete.

Which choice correctly identifies the limiting reactant and the molar concentration of the excess reactant ion in the final mixture?

A student mixes \(25.0\ \text{mL}\) of \(0.0800\ \text{M}\ \text{KI(aq)}\) with \(25.0\ \text{mL}\) of \(\text{Pb}(\text{NO}_3)_2\text{(aq)}\). The particulate representations show the ions before mixing and after \(\text{PbI}_2\text{(s)}\) forms. Every individual ion symbol represents the same amount of substance, and the same scale is used in both representations. Assume that the volumes are additive and that precipitation is complete.

Which choice correctly identifies the limiting reactant and the molar concentration of the excess reactant ion in the final mixture?

![Create a grayscale paired-panel particulate diagram with a legend above both panels mapping: large open circle = \(\text{Pb}^{2+}\), small solid black circle = \(\text{I}^-\), gray square = \(\text{K}^+\), and open triangle = \(\text{NO}_3^-\). The panel labeled “Before mixing” contains two equal-sized beakers. The left beaker holds exactly \(4\) gray squares and exactly \(4\) small solid black circles, evenly dispersed. The right beaker holds exactly \(3\) large open circles and exactly \(6\) open triangles, evenly dispersed. The panel labeled “After reaction” contains one beaker. At the bottom, place exactly \(2\) separate precipitate clusters, each containing \(1\) large open circle touching exactly \(2\) small solid black circles. Above the clusters, disperse exactly \(1\) large open circle, \(4\) gray squares, and \(6\) open triangles. No small solid black circles remain dispersed. No other particles, labels, text, or annotations appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1787301701-u1wMse.jpg)

- **A.** The limiting reactant is \(\text{Pb}(\text{NO}_3)_2\text{(aq)}\), and \([\text{I}^-]=0.0100\ \text{M}\).
- **B.** The limiting reactant is \(\text{KI(aq)}\), and \([\text{Pb}^{2+}]=0.0200\ \text{M}\).
- **C.** The limiting reactant is \(\text{KI(aq)}\), and \([\text{Pb}^{2+}]=0.0300\ \text{M}\).
- **D.** The limiting reactant is \(\text{KI(aq)}\), and \([\text{Pb}^{2+}]=0.0100\ \text{M}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120114/*