SDeterminationofPhosphoricAcidContentinSoftDrinks - DETERMINATION OF PHOSPHORIC ACID CONTENT IN SOFT DRINKS LAB PH 8 From Chemistry with Calculators

SDeterminationofPhosphoricAcidContentinSoftDrinks -...

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DETERMINATION OF PHOSPHORIC ACID CONTENT IN SOFT DRINKSLAB PH 8 From Chemistry with Calculators, Vernier Software & Technology, 2000INTRODUCTION Phosphoric acid is one of several weak acids that present in carbonated beverages. It is a component of all cola soft drinks. Phosphoric acid has a much higher concentration than other acids present in a 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 a 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: H3PO4(aq) + OH(aq) ⎯ → H2O(l) + H2PO4(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 required to reach the equivalence point will be used to determine the molarity of the H3PO4. PURPOSEThe purpose of this experiment is to determine the amount of phosphoric acid,H3PO4, in a variety of soft drinks by titrating each sample with sodium hydroxide, NaOH. MATERIALS LabPro interface 50-mL buret TI Graphing Calculator 100-mL graduated cylinder DataMate program 250-mL beaker pH Sensor ring stand various cola soft drinks, decarbonated utility clamp 0.050 M NaOH magnetic stirrer (if available) deionized water stirring bar ( or stirring rod) SAFETY Always wear goggles and an apron in the lab. Do not eat or drink in the lab. Sodium hydroxide is caustic. Avoid spilling the solution on your skin or clothing. Westminster College SIM PH8-1
Determination of Phosphoric Acid Content in Soft Drinks PROCEDURE1.Use a graduated cylinder to measure out 40 mL of a decarbonated cola soft drink and 60 mL of distilled water into a 250-mL beaker 2.Place the beaker on a magnetic stirrer and add a stirring bar. If no magnetic stirrer is available, you need to stir with a stirring rod during the titration. 3. Plug the pH Sensor into Channel 1 of the LabPro interface. Use the link cable to connect the TI Graphing Calculator to the interface. Firmly press in the cable ends. 4. Use a utility clamp to suspend the pH Sensor on a ring stand as shown in Figure 1. Position the pH Sensor in the beverage solution and adjust its position so that it is not struck by the stirring bar. 5. Obtain a 50-mL buret and rinse the buret with a few mL of the 0.050 M NaOH solution. Dispose of the rinse solution as directed by your teacher. Use a utility clamp to attach the buret to the ring stand as shown in Figure 1. Fill the buret a little above the 0.00-mL level of the buret with 0.050 M NaOH solution. Drain a small amount of NaOH solution so it fills the buret tip andleaves the NaOH at the 0.00-mL level of the buret. Record the precise concentration of the NaOH solution in your data table.

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