Antacids: Stomach Acid

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  • Topic: Antacid, PH indicator, Gastric acid
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Ninnah Gendill

CHE 112-701

Formal Lab Report

Analysis of Antacid Tablets

I. Introduction

An acid-base titration is a method of neutralizing strong acids. Unbeknownst to many, acid-base titrations occur on a daily basis. Our stomachs use acid to help us digest our food – approximately .155 hydrochloric acid (HCl) with a pH of 2-3. When too much of this acid is formed in the stomach, heartburn and other discomfort occurs. This is when people grab for their antacids; these are bases that neutralize the excess acid in the stomach.

Calcium carbonate, magnesium hydroxide, and aluminum hydroxide are all examples of bases used in antacids. In addition to these active ingredients, antacids also contain sweeteners, colourings, and “fillers” that may or may not affect the effectiveness of the neutralization. This lab will test the neutralization capacity of an antacid for comparison with other antacids. It is expected that antacids with a higher concentration of active ingredient neutralize more effectively than other antacids.

In addition to strength, special attributes that may make one antacid more desirable than another will be evaluated, as well as any mistakes that may have been made during the titrations.

II. Results

A solution of “stomach acid” was created by mixing .6M (moles/liter) hydrochloric acid (HCl) with distilled water to create a solution with a volume of 75 milliliters (mL). Methyl red, an indicator that changes colour at a pH of 4.2-6.2, was added in order to determine the equivalence point (when amount of acid equals amount of base) of the titration. This was then titrated to the end point (the indicator’s colour change) with .1M sodium hydroxide (NaOH) to discover how much base was required to neutralize the acid (Table 1). This required volume of NaOH was used in calculations to discover the neutralizing capacity of the antacid.

Table 1 – NaOH Required to Neutralize Stomach Acid

| |Volume NaOH |Volume NaOH |Volume NaOH | | |Titration #1 |Titration #2 |Titration #3 | | |(mL) |(mL) |(mL) | | | | | | |Stomach Acid |12.7 |12.0 |10.23 | | | |Average NaOH for Neutralization of Stomach Acid (mL): | |11.64 |

A weighed tablet of Maalox Regular Strength antacid (1.2485 grams after crushing) was dissolved in a 75 mL solution of .4 M HCl. This solution was further diluted to a final volume of 100 mL (concentration of .3M), and methyl red indicator was added. Three twenty-five milliliter samples of this “excess stomach acid” were titrated with .1M NaOH to the end point to discover how much acid remained after the antacid’s active ingredient calcium carbonate (CaCO3) neutralized (Table 2).

Table 2 – NaOH Required to Neutralize Excess Stomach Acid

| |Volume NaOH |Volume NaOH |Volume NaOH | | |Titration #1 |Titration #2 |Titration #3 | | |(mL) |(mL) |(mL) | |Stomach Acid...
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