Experiment 17 antacid analysis lab report

Antacid Analysis and Titration Hands-On Labs, Inc. 42-0139-00-02

Review the safety materials and wear goggles when working with chemicals. Read the entire exercise before you begin. Take time to organize the materials you will need and set aside a safe work space in which to complete the exercise.

Experiment Summary:

You will use a back-titration technique to determine the amount of acid that a commercial antacid is capable of neutralizing. You will be introduced to experimental controls, and use a control to validate the antacid neutralization analysis.

EXPERIMENT

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Learning Objectives Upon completion of this laboratory, you will be able to:

● Identify and explore the causes of acid reflux disease.

● Investigate the relationship between antacid and gastric acid and define how antacids neutralize gastric acid.

● Define titration, equivalence point, and pH indicator.

● Compare and contrast titrations and back titrations.

● Review back titration calculations and explain how control experiments are used to support experimental results.

● Perform a titration, back titration, and control experiment.

● Determine how much acid an antacid is able to neutralize.

Time Allocation: 2.5 hours

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Experiment Antacid Analysis and Titration

Materials Student Supplied Materials

Quantity Item Description 1 Bottle of distilled water 1 Dish soap 1 Metal spoon 1 Pair of scissors 1 Roll of paper towels 2 Sheets of white paper 1 Source of tap water

2-6 Thick textbooks

HOL Supplied Materials

Quantity Item Description 1 Digital scale 1 Glass Beaker, 100 mL 1 Graduated cylinder, 10 mL 1 Pair of gloves 1 Pair of safety goggles 1 Short stem pipet 1 Syringe, 10 mL 1 Stopcock 1 Test tube cleaning brush 1 Test tube clamp 1 Experiment Bag: Antacid Analysis and Titration

2- HCl, 1 M, 30 mL in dropper bottle 1- Phenolphthalein solution, 1% - 0.5 mL in pipet 2- Sodium hydroxide, 1 M - 30 mL in dropper bottle 2- Antacid tablets

Note: To fully and accurately complete all lab exercises, you will need access to:

1. A computer to upload digital camera images.

2. Basic photo editing software, such as Microsoft Word® or PowerPoint®, to add labels, leader lines, or text to digital photos.

3. Subject-specific textbook or appropriate reference resources from lecture content or other suggested resources.

Note: The packaging and/or materials in this LabPaq kit may differ slightly from that which is listed above. For an exact listing of materials, refer to the Contents List included in your LabPaq kit.

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Experiment Antacid Analysis and Titration

Background Acid Reflux Disease

If you have ever wondered what antacids are, or more specifically the chemistry behind how an antacid works, you are not alone. Antacids are used to neutralize gastric acid, a substance secreted in the stomach to promote the digestion of food. Gastric acid is produced and secreted by specialized glands in the stomach, where it functions to break down the food we consume into smaller nutrient particles so they can be absorbed by the small intestine. Gastric acid is composed primarily of hydrochloric acid (HCl), glycoproteins, and enzymes, and has a pH close to 2.0. The stomach is lined with mucus, a natural secretion that withstands and protects the stomach from direct contact with the otherwise corrosive HCl. In a healthy digestive system, the gastric acid remains in the stomach. See Figure 1.

Figure 1. Digestive System. © Leonello Calvetti

The lower end of the esophagus, the muscular tube that transports food from the mouth to the stomach, is surrounded by a ring of muscles known as the lower esophageal sphincter. The lower esophageal sphincter acts to prevent the stomach contents from moving upward into the esophagus. When this sphincter malfunctions or is otherwise compromised, gastric acid refluxes (moves back) into the esophagus resulting in acid reflux disease. Acid reflux disease causes inflammation and irritation of the esophageal lining. See Figure 2.

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Experiment Antacid Analysis and Titration

Figure 2. Gastric acid refluxes past the lower esophageal sphincter (as noted by the two arrows in the top image) and enters the esophagus, causing what is commonly known as acid reflux

disease. © Alila Sao Mai

Antacid Neutralization and Titration

While there are many ways to treat acid reflux disease, including prescription drugs, surgery, and diet modifications, the initial treatment for controlling the symptoms of acid reflux disease is through the use of over-the-counter medications, including antacids. Antacids are basic substances that neutralize, or raise the pH, of gastric acid (primarily HCl). In a neutralization reaction, the acid and the base first dissociate in solution, producing hydrogen (H+) and hydroxide (OH-) ions respectively, which then react to produce a salt and water. Commercial antacids contain a wide variety of basic substances as their active ingredient, including aluminum hydroxide (Al(OH)3), magnesium hydroxide (Mg(OH)2), sodium bicarbonate (NaHCO3), and calcium carbonate (CaCO3). See Figure 3.

Figure 3. Antacid neutralization reactions. (Top Reaction) Antacid neutralization reaction with aluminum hydroxide (Al(OH)3) as the active ingredient. (Bottom Reaction) Antacid neutralization reaction with calcium carbonate (CaCO3) as the active ingredient. Note that both reactions react

with the HCl to form a salt and water, and in the case of calcium carbonate, a gas (CO2).

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Experiment Antacid Analysis and Titration

An antacid’s effectiveness is based both qualitatively, by the physical relief it provides, and quantitatively, by calculating the amount gastric acid neutralized by the antacid. The technique used to calculate the amount of gastric acid neutralized by an antacid is titration, or more specifically, back titration. Titration is a direct, quantitative, volumetric technique, where a solution of a known concentration (titrant) is added to a solution of an unknown concentration (analyte) until the equivalence point is reached. The equivalence point of a titration, also known as a stoichiometric point, is the moment in a titration where exactly enough titrant has been added to completely react with the analyte.

A back titration is an indirect, quantitative volumetric technique where a known quantity of reagent is added to a known volume and concentration of analyte, and allowed to react. It is expected that the reaction is not complete and some analyte remains in the solution. The amount of analyte remaining is determined in a second step, by a titration reaction. A solution of known concentration (titrant) is added to the solution until the equivalence point is reached, which is indicated by a change in color. Consider, for example, a back titration to determine the amount of gastric acid neutralized by an antacid with the active ingredient aluminum hydroxide (Al(OH)3). A known mass of the Al(OH)3 containing antacid is mixed with an excess known volume and concentration of HCl and allowed to react. The remaining HCl, which was not neutralized by the antacid, is then titrated with a known concentration of NaOH until the equivalence point is reached. In this example, the antacid is the substance, the HCl is the analyte, and the NaOH is the titrant. The most effective antacid will leave the fewest HCl molecules after the reaction, and require less of the NaOH in the back titration. This back titration method can easily be used to compare the effectiveness of different antacids. The most effective antacid will leave the fewest HCl molecules after the reaction and require less of the NaOH solution in the back titration step.

In either a direct titration or indirect titration, the equivalence point can be identified through use of a pH indicator. A pH indicator is a substance that changes color when the pH of a solution changes, allowing scientists to qualitatively measure the moment when the analyte has completely reacted with the titrant. A common indicator for a titration between a weak acid and a strong base is phenolphthalein. Phenolphthalein is a pH indicator, which turns bright-pink in solutions with a pH of 8.2 or higher. Thus, equivalence points in titrations are marked by the analyte changing color from colorless to bright pink. See Figure 4 for a schematic representation of the back titration process.

There are many commercial advertisements for both

prescription and over-the-counter drugs to help with symptoms of

gastroesophageal reflux disease (GERD). GERD is simply acid reflux disease that occurs chronically, resulting in similar

symptoms and treatment as acid reflux disease.

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Experiment Antacid Analysis and Titration

Figure 4. Schematic representation of the back titration process.

Calculating Results

The quantity of HCl neutralized by the antacid is calculated indirectly by 1) calculating the amount of HCl present in the initial sample and 2) calculating the amount of HCl neutralized by the NaOH in the back-titration step. The difference between these two is the amount of HCl neutralized by the antacid.