---
title: "A student performs a gravimetric analysis to determine the mass percent of \\(\\text{BaCl}_2\\) in a solid mixture containing \\(\\text{BaCl}_2\\) and \\(\\text{NaCl}\\). The student dissolves a \\(1.250 \\text{ g}\\) sample of the mixture completely in distilled water and adds an excess of \\(0.50 \\text{ M } \\text{Na}_2\\text{SO}_4\\text{(aq)}\\) to precipitate \\(\\text{BaSO}_4\\text{(s)}\\), as represented by the net ionic equation below.  \\[ \\text{Ba}^{2+}\\text{(aq)} + \\text{SO}_4^{2-}\\text{(aq)} \\rightarrow \\text{BaSO}_4\\text{(s)} \\]  The precipitate is collected on filter paper, but the student fails to rinse the collected solid with distilled water before placing it in an oven to dry. After drying the sample to a constant mass, the student uses the measured mass of the dry solid to calculate the mass percent of \\(\\text{BaCl}_2\\) in the original mixture.  Which of the following correctly predicts the effect of this error on the calculated mass percent of \\(\\text{BaCl}_2\\), and provides the correct justification?"
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url: "https://nerd-notes.com/ubq/120166/"
date_modified: "2026-08-21T16:02:43+00:00"
---

# A student performs a gravimetric analysis to determine the mass percent of \(\text{BaCl}_2\) in a solid mixture containing \(\text{BaCl}_2\) and \(\text{NaCl}\). The student dissolves a \(1.250 \text{ g}\) sample of the mixture completely in distilled water and adds an excess of \(0.50 \text{ M } \text{Na}_2\text{SO}_4\text{(aq)}\) to precipitate \(\text{BaSO}_4\text{(s)}\), as represented by the net ionic equation below.

\[ \text{Ba}^{2+}\text{(aq)} + \text{SO}_4^{2-}\text{(aq)} \rightarrow \text{BaSO}_4\text{(s)} \]

The precipitate is collected on filter paper, but the student fails to rinse the collected solid with distilled water before placing it in an oven to dry. After drying the sample to a constant mass, the student uses the measured mass of the dry solid to calculate the mass percent of \(\text{BaCl}_2\) in the original mixture.

Which of the following correctly predicts the effect of this error on the calculated mass percent of \(\text{BaCl}_2\), and provides the correct justification?

A student performs a gravimetric analysis to determine the mass percent of \(\text{BaCl}_2\) in a solid mixture containing \(\text{BaCl}_2\) and \(\text{NaCl}\). The student dissolves a \(1.250 \text{ g}\) sample of the mixture completely in distilled water and adds an excess of \(0.50 \text{ M } \text{Na}_2\text{SO}_4\text{(aq)}\) to precipitate \(\text{BaSO}_4\text{(s)}\), as represented by the net ionic equation below.

\[ \text{Ba}^{2+}\text{(aq)} + \text{SO}_4^{2-}\text{(aq)} \rightarrow \text{BaSO}_4\text{(s)} \]

The precipitate is collected on filter paper, but the student fails to rinse the collected solid with distilled water before placing it in an oven to dry. After drying the sample to a constant mass, the student uses the measured mass of the dry solid to calculate the mass percent of \(\text{BaCl}_2\) in the original mixture.

Which of the following correctly predicts the effect of this error on the calculated mass percent of \(\text{BaCl}_2\), and provides the correct justification?

- **A.** The calculated mass percent will be too high because non-volatile dissolved solutes from the supernatant crystallize upon drying, resulting in an erroneously large measured precipitate mass and an overestimated number of moles of \(\text{Ba}^{2+}\).
- **B.** The calculated mass percent will be too high because the unwashed solid retains water that permanently increases the molar mass of \(\text{BaSO}_4\) used in the stoichiometric calculation.
- **C.** The calculated mass percent will be too low because unwashed \(\text{BaSO}_4\text{(s)}\) particles redissolve into the residual supernatant liquid and pass through the filter paper during heating.
- **D.** The calculated mass percent will be too low because the mass of the unwashed \(\text{NaCl}\) impurity is incorrectly added to the denominator of the mass percent formula.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120166/*