---
title: "A student standardizes a sample of an \\(\\text{Fe}^{2+}\\text{(aq)}\\) solution by titrating a \\(25.00\\text{ mL}\\) aliquot with standardized \\(0.0200\\text{ M }\\text{KMnO}_4\\text{(aq)}\\) in an acidic medium according to the balanced equation below:  \\[ 5\\,\\text{Fe}^{2+}\\text{(aq)} + \\text{MnO}_4^-\\text{(aq)} + 8\\,\\text{H}^+\\text{(aq)} \\rightarrow 5\\,\\text{Fe}^{3+}\\text{(aq)} + \\text{Mn}^{2+}\\text{(aq)} + 4\\,\\text{H}_2\\text{O(l)} \\]  Before beginning the titration, an air bubble was trapped in the buret tip below the stopcock. During the titration, the air bubble was dislodged and filled with titrant solution as liquid was delivered into the flask to reach the light-pink endpoint. Which of the following correctly predicts the effect of this error on the calculated \\([\\text{Fe}^{2+}]\\) and identifies the proper procedural modification to eliminate this source of error?"
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url: "https://nerd-notes.com/ubq/121403/"
date_modified: "2026-08-23T05:02:06+00:00"
---

# A student standardizes a sample of an \(\text{Fe}^{2+}\text{(aq)}\) solution by titrating a \(25.00\text{ mL}\) aliquot with standardized \(0.0200\text{ M }\text{KMnO}_4\text{(aq)}\) in an acidic medium according to the balanced equation below:

\[ 5\,\text{Fe}^{2+}\text{(aq)} + \text{MnO}_4^-\text{(aq)} + 8\,\text{H}^+\text{(aq)} \rightarrow 5\,\text{Fe}^{3+}\text{(aq)} + \text{Mn}^{2+}\text{(aq)} + 4\,\text{H}_2\text{O(l)} \]

Before beginning the titration, an air bubble was trapped in the buret tip below the stopcock. During the titration, the air bubble was dislodged and filled with titrant solution as liquid was delivered into the flask to reach the light-pink endpoint. Which of the following correctly predicts the effect of this error on the calculated \([\text{Fe}^{2+}]\) and identifies the proper procedural modification to eliminate this source of error?

A student standardizes a sample of an \(\text{Fe}^{2+}\text{(aq)}\) solution by titrating a \(25.00\text{ mL}\) aliquot with standardized \(0.0200\text{ M }\text{KMnO}_4\text{(aq)}\) in an acidic medium according to the balanced equation below:

\[ 5\,\text{Fe}^{2+}\text{(aq)} + \text{MnO}_4^-\text{(aq)} + 8\,\text{H}^+\text{(aq)} \rightarrow 5\,\text{Fe}^{3+}\text{(aq)} + \text{Mn}^{2+}\text{(aq)} + 4\,\text{H}_2\text{O(l)} \]

Before beginning the titration, an air bubble was trapped in the buret tip below the stopcock. During the titration, the air bubble was dislodged and filled with titrant solution as liquid was delivered into the flask to reach the light-pink endpoint. Which of the following correctly predicts the effect of this error on the calculated \([\text{Fe}^{2+}]\) and identifies the proper procedural modification to eliminate this source of error?

- **A.** The calculated \([\text{Fe}^{2+}]\) will be too low because the trapped air decreases the total volume of \(\text{KMnO}_4\text{(aq)}\) delivered, leading to a smaller recorded volume; to eliminate this error, titrant should be flushed through the tip into a waste container before recording the initial volume.
- **B.** The calculated \([\text{Fe}^{2+}]\) will be too low because atmospheric oxygen in the trapped air bubble oxidizes a portion of the \(\text{Fe}^{2+}\text{(aq)}\) analyte prior to the reaction; to eliminate this error, the analyte solution should be boiled to remove dissolved gases before titration.
- **C.** The calculated \([\text{Fe}^{2+}]\) will be too high because the recorded volume of \(\text{KMnO}_4\text{(aq)}\) is greater than the volume that actually reached the flask; to eliminate this error, the buret should be rinsed thoroughly with deionized water immediately after filling with titrant.
- **D.** The calculated \([\text{Fe}^{2+}]\) will be too high because the recorded volume of \(\text{KMnO}_4\text{(aq)}\) is greater than the volume that actually reached the flask; to eliminate this error, titrant should be flushed through the tip into a waste container before recording the initial volume.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/121403/*