DRAFT: This module has unpublished changes.

Introduction:

The goal of this experiment is to determine the Calcium Carbonate content of an anti-acid pill. A secondary goal is to learn how to properly titrate a solution.

I hypothesize that by adding a known volume of HCl of a set concentration to a known mass of Calcium Carbonate, and boiling it, that, provided one properly took stoichiometric ratios into account, that one can react all of the Calcium Carbonate with HCl, and have a remaining volume of HCl in the solution. One can then titrate the solution with a standardized NaOH solution, and thus knowing the stoichiometric ratio between the NaOH and HCl, calculate how much of the HCl solution was remaining. Then, by subtracting this from the total amount of HCl solution added initially, one can determine how much HCl reacted with the Calcium Carbonate, and then by accounting for stoichiometry, how many moles of Calcium Carbonate were in the pill. Then, one can use the formula weight of Calcium Carbonate to determine how many grams of Calcium Carbonate were in the pill, or, if so desired, the percentage of the pill that is made of Calcium Carbonate.

 

Equipment:

  • Data Collection System
  • pH Sensor
  • Magnetic Stirrer
  • Ring Stand
  • Beaker (2), 100-mL
  • Beaker (2), 10-mL
  • Volumetric Flask, 1000-mL
  • Erlenmeyer Flask, 250-mL
  • Hot Plate/Magnetic Plate
  • Mesh Pad, with Asbestos
  • Automatic Titrator
  • Funnel
  • Jar with custom-made hockey puck-derived lid, 240-mL
  • Hydrochloric Acid (HCl) solution, standardized in Lab 7a, 100 mL
  • Sodium Hydroxide (NaOH) solution, standardized in Lab 6a, 100 mL
  • Anti-Acid Pill
  • Mortar and Pestle
  • Buffers, pH 4 and pH 10, 10 mL
  • Water, deionized, 100 mL
  • Plastic Bottle, 1-L
  • Wash Bottle
  • Pipet
  • Aluminum Foil
  • Tissue

Method:

  • Gathered all equipment and materials. Inspected all equipment for damage or contamination. Hotplate/Magnetic Plate and Stand were already assembled.
  • Ground pill into fine powder via mortar and pestle.
  • Weighed out about 1.0 g of the powder, and washed into 250 mL Erlenmeyer Flask.
  • Added 100.00 mL of HCl solution, standardized in lab 7a (about 0.1 M).
  • Placed Erlenmeyer flask on hot plate, and heated for 5 minutes.
  • Placed flask on mesh pad and allowed to cool.
  • Transfered solution to 240 mL Titration Jar. Cleaned Erlenmeyer Flask. Prepared 3 solutions in total, via the same method.
  • Started a new experiment with the data collection system. Set up graph.
  • Set up the Titrator, flushing it once with deionized water.
  • Calibrated the pH sensor, by rinsing it, measuring the pH of the buffer solutions, taking care to rinse the sensor between measurements, and then testing it with the buffers again.
  • Added the magnetic stirrer to the end of the pH sensor, and passed it through the hockey-puck lid, and into the jar, ensuring that the entire apparatus was secured to the stand.
  • Loaded the Titrator with the NaOH titrant that was standardized in Lab 6a.
  • Attached jar to the hockey puck lid. Ensured that the pH sensor was submerged within the solution.
  • Activated magnetic stirrer, and set to a mid-range speed.
  • Activated the Titrator, running beyond the equilibrium point, until the pH curve had flattened, ensuring that the system was recording at the time.
  • Repeated with a second and third trial solution.
  • Recorded data, saved graph, and flushed titrator with deionized water.
  • Cleaned all glassware, set them to dry in their designated areas, and returned all equipment to its point of origin.

 

Data Analysis:

 

The average Calcium Carbonate content of the sample is 38.10%.

 

Conclusion:

The goal of this experiment is to determine the Calcium Carbonate content of an anti-acid pill. By adding a known volume of HCl of a set concentration to a known mass of Calcium Carbonate, and boiling it, one can react all of the Calcium Carbonate with HCl, and have a remaining volume of HCl in the solution. One can then titrate the solution with a standardized NaOH solution, and, knowing the stoichiometric ratio between the NaOH and HCl, calculate how much of the HCl solution was remaining. Then, by subtracting this from the total amount of HCl solution added initially, one can determine how much HCl reacted with the Calcium Carbonate, and then by accounting for stoichiometry, how many moles of Calcium Carbonate were in the pill. Then, one can use the formula weight of Calcium Carbonate to determine how many grams of Calcium Carbonate were in the pill, or, if so desired, the percentage of the pill that is made of Calcium Carbonate.

 

The average Calcium Carbonate content of the sample is 38.10%.

 

As the average experimental Calcium Carbonate content is 38.10%, and the expected Calcium Carbonate concentration is 35.50%, this indicates error within the experiment that should be further examined.

Trial 1: 6.090%

Trial 2: 8.771%

Trial 3: 7.112%

 

Possible sources of error include:

  • Failure to properly measure (or standardize) the concentration of the NaOH solution.
  • Failure to titrate beyond the equivalence point (making determining the point at which the two solutes had completely reacted impossible).
  • Failure to keep the solution mixed while titrating, introducing the possibility that the solution may not completely react in areas, and the possibility of inaccurate measurement.
  • Failure to properly flush the titrator before beginning the experiment, either contaminating the solution, or diluting it with residual deionized water.
  • Failure to properly handle the solutions, introducing the likelihood of contamination (NaOH can react with carbon dioxide in the air, while the HCl can leave solution, and return to its gaseous state), thus disrupting measurements.
  • Failure to properly measure the Calcium Carbonate (measuring mass, then grinding it would be one such example, as would be taking too much). Both of these would disrupt further measurements.
  • Human error is always in effect, given that the laboratory does not function under ideal conditions. As such, there is always the possibility of inaccuracies with measurement, perception of measurement, inaccuracies of equipment, and other such errors. (However, this is not likely to be the sole cause of the inaccuracies within this experiment, though it may contribute to it.)

 

Possible improvements that one could make to the experiment include using a more accurate pH probe, using more accurate balances (relating back to Lab 6a, and the standardization of the NaOH titrant), using a more accurate titrator (the syringe could be made more accurate), ensuring that lab partners read the experiment beforehand (increasing familiarity with the procedure, and minimizing human error), preparing the solutions in an atmosphere that lacks carbon dioxide (to avoid reaction of the NaOH solution), keeping the HCl solution covered (to minimize inaccuracies caused by it leaving solution) and repeating the experiment multiple times (to minimize the impact of an anomalous result).

DRAFT: This module has unpublished changes.