Gravimetric Analysis of Calcium Carbonate in Antacid

🔒 LAB RESOURCES:

  • Student Procedure [PDF] [DOC]

  • Teacher Annotated Procedure [PDF]

  • Complete Lab Guide [HERE]

  • GoogleSheet Data & Analysis [HERE]

Download Procedure (pdf)

SUMMARY/ OVERVIEW:

Students determine the amount of calcium carbonate ($\text{CaCO}_3$) in an antacid tablet using gravimetric analysis. The $\text{CaCO}_3$ is dissolved in acid, precipitated as calcium oxalate ($\text{CaC}_2\text{O}_4$), and then heated to convert it to a precise, weighable form, usually $\text{CaO}$. The final mass is used to calculate the original $\text{CaCO}_3$ mass and percent composition.

ESTIMATE TIME ⏰: 40-60 minutes

  • Dissolution and Precipitation (1 hour)

  • Drying and Final Measurement (15 minutes)

A diagonal arrangement of four colored squares: blue, yellow, red, and black.

SAFETY PRECAUTIONS:

Eye Protection is Mandatory: Always wear approved safety goggles throughout the entire experiment.

Handle Strong Acids with Care: The procedure requires the use of Hydrochloric Acid ($\text{HCl}$), a corrosive substance. If acid contacts skin, immediately rinse the area with copious amounts of water and notify the instructor.

Proper Waste Disposal: Dispose of all chemical waste, especially the filtrate and any remaining reagents, in the designated waste containers as instructed by your teacher. Do not pour chemicals down the sink.

Remember, consult the Safety Data Sheets (SDS) for each chemical for a more comprehensive understanding of the specific hazards and proper handling procedures. Always work in a well-ventilated area and notify your instructor immediately in case of any spills or accidents.

Introduction

Calcium carbonate acts as a base in antacids. When it encounters stomach acid (primarily hydrochloric acid, HCl), it undergoes a neutralization reaction. This reaction consumes the acid, reducing its concentration and providing relief from heartburn or indigestion.

Here's the chemical equation that represents this process:

CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l)

However, antacids often contain other ingredients like binders and flavorings. Gravimetric analysis provides a powerful tool to isolate and quantify the amount of calcium carbonate present in these tablets.

This lab will take you through a series of steps, including precipitation, filtration, drying, and weighing, to separate and quantify the calcium carbonate. By carefully measuring the mass of the isolated CaCO3 and using some chemical calculations, you'll be able to determine the percentage of calcium carbonate present in your antacid tablet.

Gravimetric Analysis

Gravimetric analysis is a quantitative technique used to determine the mass or concentration of a specific substance (called the analyte) present in a sample. It achieves this by converting the analyte into a weighable product through a series of clever steps.

A three-step diagram illustrating a chemical process: Step 1 shows dissolving solid soluble salt with lead ions in a beaker; Step 2 depicts adding a solution containing sulfate ions to form solid lead sulfate; Step 3 demonstrates filtering and weighing the solid lead sulfate and remaining solution with other chemical species.

The following are the general steps of gravimetric analysis

  1. Precipitation: A carefully chosen chemical reaction reacts the target analyte (ion in solution) — for this lab it is the calcium — into a solid precipitate. The selectivity of the reaction ensures that the precipitate specifically isolates the analyte from other components in the mixture.

  2. Separation: The precipitate is then separated from the remaining liquid portion (supernatant) using filtration techniques. This physical separation process minimizes the inclusion of unwanted components from the original mixture.

  3. Purification: The isolated precipitate might contain traces of impurities adhering to its surface. Washing steps with appropriate solvents are employed to remove these contaminants, ensuring the precipitate accurately represents the pure analyte.

  4. Weighing: After complete drying to remove any moisture, the purified precipitate is meticulously weighed using an analytical balance with high precision. This recorded weight serves as a critical quantitative measurement for subsequent calculations.

  5. Calculations: Using the established stoichiometry of the precipitation reaction and the weight of the isolated precipitate, calculations are performed to determine the mass of the analyte originally present in the sample. Alternatively, the percentage by weight of the analyte in the sample can be calculated.

Key Points:

One of the main ingredients in antacid tablets (such as Rolaids, Tums etc.) is calcium carbonate, which helps to neutralize stomach acid in the following general reaction; Acid + Carbonate è Salt + Water + Carbon Dioxide

There are also a number of other ingredients in these tablets such as binders, that hold the tablet together, but that you can assume contain no calcium or carbonate ions

In the lab, we can mimic the action of antacids in the stomach by reacting the calcium carbonate with hydrochloric acid (often helped by the addition of a few mL of distilled water and some very gentle heating). The binding materials will not dissolve, i.e., they are insoluble in acid

Aqueous calcium ions can be precipitated by the use of a solution of carbonate ions

When relevant, always give thought to dependent and independent variables and controls