---
title: "A student heats a sample of hydrated cobalt(II) chloride, \\(\\text{CoCl}_2 \\cdot x\\text{H}_2\\text{O}\\), in a crucible to determine the integer value of \\(x\\). The student heats the crucible once, allows it to cool, and measures the mass of the solid residue without performing additional heating cycles to verify constant mass. If the heating was incomplete and some water of hydration remained bound in the residue, which of the following correctly predicts and explains the effect of this error on the calculated value of \\(x\\)?"
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url: "https://nerd-notes.com/ubq/120160/"
date_modified: "2026-08-21T16:02:40+00:00"
---

# A student heats a sample of hydrated cobalt(II) chloride, \(\text{CoCl}_2 \cdot x\text{H}_2\text{O}\), in a crucible to determine the integer value of \(x\). The student heats the crucible once, allows it to cool, and measures the mass of the solid residue without performing additional heating cycles to verify constant mass. If the heating was incomplete and some water of hydration remained bound in the residue, which of the following correctly predicts and explains the effect of this error on the calculated value of \(x\)?

A student heats a sample of hydrated cobalt(II) chloride, \(\text{CoCl}_2 \cdot x\text{H}_2\text{O}\), in a crucible to determine the integer value of \(x\). The student heats the crucible once, allows it to cool, and measures the mass of the solid residue without performing additional heating cycles to verify constant mass. If the heating was incomplete and some water of hydration remained bound in the residue, which of the following correctly predicts and explains the effect of this error on the calculated value of \(x\)?

- **A.** The calculated value of \(x\) will be greater than the true value because the presence of unevaporated water causes the calculated mass of water lost to be overestimated.
- **B.** The calculated value of \(x\) will be less than the true value because the calculated mass of water lost is too low and the calculated mass of anhydrous \(\text{CoCl}_2\) is too high.
- **C.** The calculated value of \(x\) will be less than the true value because the unevaporated water decreases the measured initial mass of the hydrate before heating.
- **D.** The calculated value of \(x\) will be greater than the true value because the unevaporated water increases the calculated moles of anhydrous \(\text{CoCl}_2\), which increases the mole ratio of \(\text{H}_2\text{O}\) to \(\text{CoCl}_2\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/120160/*