---
title: "A student performs an experiment to determine the percent by mass of \\(\\text{CaCO}_3\\text{(s)}\\) in an impure mineral sample using the mass loss of evolved \\(\\text{CO}_2\\text{(g)}\\). The intended reaction is represented by the following net ionic equation:  \\[\\text{CaCO}_3\\text{(s)} + 2\\,\\text{H}^+\\text{(aq)} \\rightarrow \\text{Ca}^{2+}\\text{(aq)} + \\text{H}_2\\text{O(l)} + \\text{CO}_2\\text{(g)}\\]  The student places a \\(3.00\\text{ g}\\) sample into a beaker, adds an excess of \\(1.0\\text{ M }\\text{HCl(aq)}\\), and records the total mass of the beaker and its contents over time until the mass stops decreasing. In a second trial using an identical \\(3.00\\text{ g}\\) sample, the student mistakenly substitutes \\(1.0\\text{ M }\\text{H}_2\\text{SO}_4\\text{(aq)}\\) for \\(1.0\\text{ M }\\text{HCl(aq)}\\). The student observes that bubbling ceases prematurely while unreacted solid remains at the bottom of the beaker. Which of the following best predicts and explains the effect of this error on the calculated percent by mass of \\(\\text{CaCO}_3\\text{(s)}\\)?"
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url: "https://nerd-notes.com/ubq/123682/"
date_modified: "2026-09-28T12:01:58+00:00"
---

# A student performs an experiment to determine the percent by mass of \(\text{CaCO}_3\text{(s)}\) in an impure mineral sample using the mass loss of evolved \(\text{CO}_2\text{(g)}\). The intended reaction is represented by the following net ionic equation:

\[\text{CaCO}_3\text{(s)} + 2\,\text{H}^+\text{(aq)} \rightarrow \text{Ca}^{2+}\text{(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}\]

The student places a \(3.00\text{ g}\) sample into a beaker, adds an excess of \(1.0\text{ M }\text{HCl(aq)}\), and records the total mass of the beaker and its contents over time until the mass stops decreasing. In a second trial using an identical \(3.00\text{ g}\) sample, the student mistakenly substitutes \(1.0\text{ M }\text{H}_2\text{SO}_4\text{(aq)}\) for \(1.0\text{ M }\text{HCl(aq)}\). The student observes that bubbling ceases prematurely while unreacted solid remains at the bottom of the beaker. Which of the following best predicts and explains the effect of this error on the calculated percent by mass of \(\text{CaCO}_3\text{(s)}\)?

A student performs an experiment to determine the percent by mass of \(\text{CaCO}_3\text{(s)}\) in an impure mineral sample using the mass loss of evolved \(\text{CO}_2\text{(g)}\). The intended reaction is represented by the following net ionic equation:

\[\text{CaCO}_3\text{(s)} + 2\,\text{H}^+\text{(aq)} \rightarrow \text{Ca}^{2+}\text{(aq)} + \text{H}_2\text{O(l)} + \text{CO}_2\text{(g)}\]

The student places a \(3.00\text{ g}\) sample into a beaker, adds an excess of \(1.0\text{ M }\text{HCl(aq)}\), and records the total mass of the beaker and its contents over time until the mass stops decreasing. In a second trial using an identical \(3.00\text{ g}\) sample, the student mistakenly substitutes \(1.0\text{ M }\text{H}_2\text{SO}_4\text{(aq)}\) for \(1.0\text{ M }\text{HCl(aq)}\). The student observes that bubbling ceases prematurely while unreacted solid remains at the bottom of the beaker. Which of the following best predicts and explains the effect of this error on the calculated percent by mass of \(\text{CaCO}_3\text{(s)}\)?

- **A.** The calculated percent is too high because \(\text{H}_2\text{SO}_4\text{(aq)}\) donates two protons per formula unit, producing twice as many moles of \(\text{CO}_2\text{(g)}\) per mole of acid added.
- **B.** The calculated percent is too high because the higher molar mass of \(\text{SO}_4^{2-}\text{(aq)}\) compared to \(\text{Cl}^-\text{(aq)}\) increases the mass of solution remaining in the beaker, making the calculated mass loss greater.
- **C.** The calculated percent is too low because \(\text{HSO}_4^-\text{(aq)}\) forms a buffer system that neutralizes \(\text{CO}_3^{2-}\) ions without forming \(\text{CO}_2\text{(g)}\) or \(\text{H}_2\text{O(l)}\).
- **D.** The calculated percent is too low because the precipitation of sparingly soluble \(\text{CaSO}_4\text{(s)}\) coats the \(\text{CaCO}_3\text{(s)}\) particles, preventing complete reaction with \(\text{H}^+\text{(aq)}\) and releasing less \(\text{CO}_2\text{(g)}\).

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/123682/*