Vernier Software & Technology

Determining the Phosphoric Acid Content in Soft Drinks

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 Vernier sensors and equipment.

Option 2

You may also need an interface and software for data collection. What do I need for data collection?

Chemistry with Vernier

See other experiments from the lab book.

 1 Endothermic and Exothermic Reactions 2 Freezing and Melting of Water 3 Another Look at Freezing Temperature 4 Heat of Fusion of Ice 5 Find the Relationship: An Exercise in Graphing Analysis 6 Boyle's Law: Pressure-Volume Relationship in Gases 7 Pressure-Temperature Relationship in Gases 8 Fractional Distillation 9 Evaporation and Intermolecular Attractions 10 Vapor Pressure of Liquids 11 Determining the Concentration of a Solution: Beer's Law 12 Effect of Temperature on Solubility of a Salt 13 Properties of Solutions: Electrolytes and Non-Electrolytes 14 Conductivity of Solutions: The Effect of Concentration 15 Using Freezing Point Depression to Find Molecular Weight 16 Energy Content of Foods 17 Energy Content of Fuels 18 Additivity of Heats of Reaction: Hess's Law 19 Heat of Combustion: Magnesium 20 Chemical Equilibrium: Finding a Constant, Kc 21 Household Acids and Bases 22 Acid Rain 23 Titration Curves of Strong and Weak Acids and Bases 24 Acid-Base Titration 25 Titration of a Diprotic Acid: Identifying an Unknown 26 Using Conductivity to Find an Equivalence Point 27 Acid Dissociation Constant, Ka 28 Establishing a Table of Reduction Potentials: Micro-Voltaic Cells 29 Lead Storage Batteries 30 Rate Law Determination of the Crystal Violet Reaction 31 Time-Release Vitamin C Tablets 32 The Buffer in Lemonade 33 Determining the Free Chlorine Content of Swimming Pool Water 34 Determining the Quantity of Iron in a Vitamin Tablet 35 Determining the Phosphoric Acid Content in Soft Drinks 36 Microscale Acid-Base Titration

Experiment 35 from Chemistry with Vernier Lab Book

Included in the Lab Book

Vernier lab books include word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.