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Determining the Phosphoric Acid Content in Soft Drinks

Experiment #35 from Chemistry with Vernier

Education Level
High School
Subject
Chemistry

Introduction

Phosphoric acid is one of several weak acids that exist in carbonated beverages. It is a component of all cola soft drinks. Phosphoric acid has a much higher concentration than other acids in a container of soft drink, so its concentration can be determined by a simple acid-base titration.

In this experiment, you will titrate a sample of a cola soft drink with sodium hydroxide solution and determine the concentration of phosphoric acid, H3PO4. Hydrogen ions from the first dissociation of phosphoric acid react with hydroxide ions from the NaOH in a one-to-one ratio in the overall reaction:

{{\text{H}}_{\text{3}}}{\text{P}}{{\text{O}}_{\text{4}}}{\text{(aq) + O}}{{\text{H}}^{\text{ - }}}{\text{(aq)}} \to {{\text{H}}_{\text{2}}}{\text{O(1) + }}{{\text{H}}_{\text{2}}}{\text{P}}{{\text{O}}_{\text{4}}}^{\text{ - }}{\text{(aq)}}

In this experiment, you will use a pH Sensor to monitor pH as you titrate. The region of most rapid pH change will then be used to determine the equivalence point. The volume of NaOH titrant used at the equivalence point will be used to determine the molarity of the H3PO4.

Objectives

In this experiment, you will

  • Use a pH Sensor to monitor pH during the titration of phosphoric acid in a cola soft drink.
  • Using the titration equivalence point, determine the molarity of H3PO4.

Sensors and Equipment

This experiment features the following sensors and equipment. Additional equipment may be required.

Option 1

Go Direct® pH Sensor

Option 2

pH Sensor

Option 3

Go Direct® Drop Counter
Precision Volume Dispenser

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This experiment is #35 of Chemistry with Vernier. The experiment in the book includes student instructions as well as instructor information for set up, helpful hints, and sample graphs and data.

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