Procedure: Phosphoric acid content

Procedure: Phosphoric acid content of Coca-Cola
The beverage “Coca-Cola” contains significant amounts of phosphoric acid and phosphate salts and these can
be evaluated by titration. However, since beverages also contain carbonic acid, a necessary preliminary step is
elimination of this species. To shorten the lab, the Coke has been boiled already.
pH ELECTRODES ARE FRAGILE AND VERY EXPENSIVE!
They are easily damaged, so please take care when handling them !
1. Take a 100.0mL aliquot of the boiled beverage in a 250mL beaker.
2. Place the beaker on the magnetic stirrer, add the stirrer “bug” (more correctly a magnetic
follower) and carefully clamp the burette into position above the beaker (so that you can
comfortably add base) and the pH electrode into position. Turn the stirrer on and make sure that
it does not come into contact with the pH electrode. Stirring should be a steady, constant rate
– not too rapid. This will help achieve effective mixing with each addition of the base.
3. With the pH electrode in place, titrate the solution with standard (approximately 0.10M NaOH
– record the exact concentration) sodium hydroxide solution, recording the pH after each
addition. The first two additions of titrant volume (Vb) can large (about 1 mL), as the pH change
at this point in the titration is only small (see diagram on page 15). The volume added should
however be decreased beyond this point the pH will begin to rise rapidly. You will need
to make adjustments to Vb based on the change in ΔpH / ΔV. Make sure that you calculate
ΔpH/ΔV for each new Vb addition as this will show when you are nearing the titration end-point
(by becoming large). When the pH is changing rapidly record the volume of addition should be
reduced to no more than 0.1mL - 0.2mL.

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Procedure: Phosphoric acid content of Coca-Cola
beverage The "Coca-Cola" Contains significant amounts of phosphoric acid and phosphate salts and Can these
be evaluated by Titration. However, since beverages also contain Carbonic acid, is a necessary Preliminary Step
Elimination of this Species. To Shorten The Lab, The Coke has been Boiled Already.
pH ELECTRODES ARE FRAGILE AND VERY EXPENSIVE!
They are easily damaged, So please Take Care When Handling them!
1. Take a 100.0mL aliquot of The Boiled beverage in a 250mL beaker.
2. The Place beaker on The Magnetic stirrer, stirrer Add The "Bug" (more correctly a Magnetic
Follower) and carefully position above Clamp The burette Into The beaker (So that You Can
Comfortably Add Base) and Into The pH electrode position. The stirrer turn on and Make sure that
it does Not Come Into Contact with The pH electrode. Stirring should be a Steady, Constant rate
- Not Too Rapid. This Will Help Achieve Effective mixing with each addition of The Base.
3. The pH electrode with in Place, The Solution titrate with standard (approximately 0.10m NaOH
- The exact record Concentration) Sodium hydroxide Solution, The pH recording After each
addition. The First Two Additions of Titrant volume (Vb) Can Large (About 1 mL), Change As The pH
Titration is only at this Point in The Small (See diagramSponsored on page 15). The added volume should
however be decreased Beyond this Point The pH Will Begin to Rise rapidly. You Will Need
to Make adjustments to Vb based on The Change in ΔpH / ΔV. Make sure that You Calculate
ΔpH / ΔV for each New addition Vb As this show When Will You are nearing The Titration End-Point
(by Becoming Large). When The pH is rapidly record Changing The volume of addition should be
reduced to no more than 0.1ml - 0.2mL.