---
title: "A student performs a gravimetric analysis experiment to determine the number of moles of water of crystallization, \\(x\\), per mole of anhydrous cobalt(II) chloride in a hydrated sample, \\(\\text{CoCl}_2 \\cdot x\\text{H}_2\\text{O}\\). The theoretical value of \\(x\\) is \\(6\\). The student heats the sample in a covered crucible over a Bunsen burner, cools the crucible to room temperature in a desiccator, and records the mass after successive heatings. The collected data are shown in the table below.  | Measurement | Mass | | :— | :— | | Mass of empty crucible and lid | \\(24.500 \\text{ g}\\) | | Mass of crucible, lid, and hydrated sample | \\(26.879 \\text{ g}\\) | | Mass of crucible, lid, and sample after first heating | \\(25.900 \\text{ g}\\) | | Mass of crucible, lid, and sample after second heating | \\(25.800 \\text{ g}\\) | | Mass of crucible, lid, and sample after third heating (intense heating) | \\(25.562 \\text{ g}\\) |  When the student calculates the value of \\(x\\) using the mass recorded after the third heating, the resulting value is significantly greater than \\(6\\). Which of the following best explains why using the data from the third heating leads to an experimental value of \\(x\\) that is too large?"
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url: "https://nerd-notes.com/ubq/123670/"
date_modified: "2026-09-28T12:01:56+00:00"
---

# A student performs a gravimetric analysis experiment to determine the number of moles of water of crystallization, \(x\), per mole of anhydrous cobalt(II) chloride in a hydrated sample, \(\text{CoCl}_2 \cdot x\text{H}_2\text{O}\). The theoretical value of \(x\) is \(6\). The student heats the sample in a covered crucible over a Bunsen burner, cools the crucible to room temperature in a desiccator, and records the mass after successive heatings. The collected data are shown in the table below.

| Measurement | Mass |
| :— | :— |
| Mass of empty crucible and lid | \(24.500 \text{ g}\) |
| Mass of crucible, lid, and hydrated sample | \(26.879 \text{ g}\) |
| Mass of crucible, lid, and sample after first heating | \(25.900 \text{ g}\) |
| Mass of crucible, lid, and sample after second heating | \(25.800 \text{ g}\) |
| Mass of crucible, lid, and sample after third heating (intense heating) | \(25.562 \text{ g}\) |

When the student calculates the value of \(x\) using the mass recorded after the third heating, the resulting value is significantly greater than \(6\). Which of the following best explains why using the data from the third heating leads to an experimental value of \(x\) that is too large?

A student performs a gravimetric analysis experiment to determine the number of moles of water of crystallization, \(x\), per mole of anhydrous cobalt(II) chloride in a hydrated sample, \(\text{CoCl}_2 \cdot x\text{H}_2\text{O}\). The theoretical value of \(x\) is \(6\). The student heats the sample in a covered crucible over a Bunsen burner, cools the crucible to room temperature in a desiccator, and records the mass after successive heatings. The collected data are shown in the table below.

| Measurement | Mass |
| :--- | :--- |
| Mass of empty crucible and lid | \(24.500 \text{ g}\) |
| Mass of crucible, lid, and hydrated sample | \(26.879 \text{ g}\) |
| Mass of crucible, lid, and sample after first heating | \(25.900 \text{ g}\) |
| Mass of crucible, lid, and sample after second heating | \(25.800 \text{ g}\) |
| Mass of crucible, lid, and sample after third heating (intense heating) | \(25.562 \text{ g}\) |

When the student calculates the value of \(x\) using the mass recorded after the third heating, the resulting value is significantly greater than \(6\). Which of the following best explains why using the data from the third heating leads to an experimental value of \(x\) that is too large?

- **A.** Water remained in the sample after the first two heatings; unevaporated water was incorrectly included in the mass of the anhydrous residue, which increased the calculated mole ratio of \(\text{H}_2\text{O}\) to \(\text{CoCl}_2\).
- **B.** Thermal decomposition of \(\text{CoCl}_2\) occurred during the third heating; this caused the calculated mass of \(\text{CoCl}_2\) to be too large and the calculated mass of \(\text{H}_2\text{O}\) to be too small, resulting in an overestimate of \(x\).
- **C.** Thermal decomposition of \(\text{CoCl}_2\) occurred during the third heating; the loss of volatile decomposition products falsely increased the calculated mass of \(\text{H}_2\text{O}\) and decreased the calculated mass of \(\text{CoCl}_2\), resulting in an overestimate of \(x\).
- **D.** The sample absorbed atmospheric moisture prior to the third heating; this additional mass falsely increased the calculated moles of \(\text{H}_2\text{O}\) released, resulting in an overestimate of \(x\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123670/*