Titration of a cola product.

IV. Materials:

Equipment-pH electrode, thermistor, stirring rod, styrofoam cups, beakers, watch glass, hot plate, pipette.

Reagents-cola, 0.01 M NaOH

V. Safety Precautions:

Wear safety glasses. If the acid or base solutions get on your skin, rinse with plenty of water. All solutions resulting from titrations may be discarded in the sink. Any unused solution should not be returned to the storage containers; therefore, take only the amounts of solution that you will need.

VI. Experimental Procedure:

Before using the pH electrode and/or thermistor, they must be calibrated. You should obtain temperature and/or pH, and volume data for at least 10 mL beyond the equivalence point. You should stir the solution with a stirring rod or magnetic stirrer at all times, leaving the thermistor and/or pH electrode stationary in the styrofoam cup. Once the experiment is complete, you can call up your data files on the spreadsheet for graphing.

. Pour about 75 mL of cola into a clean, dry 250 mL beaker.

2. To prepare the cola for titration, it must first be decarbonated. Cover the beaker containing the cola with a watch glass and gently boil for about 20 minutes using a hot plate. This will remove the CO2 from the cola, which would interfere with the phosphoric acid titration.

3. Let the cola to cool to room temperature before titrating.

4. Using a pipette, add 25.00 mL of room temperature, decarbonated cola into a clean, double-nested styrofoam cup.

5. Using a 250 mL beaker, obtain about 75 mL of 0.01 M NaOH. Note the exact concentration of the NaOH from the container.

6. To prepare the buret for the titration, it should first be rinsed with distilled water and the rinsed with several small portions of the NaOH solution. To begin the titration, the buret should contain between 40 and 50 mL of NaOH.

VII. Data:

Trial 1-25 mL of decarbonated Pepsi, 0.01 M NaOH used for the titration, and only 8 mL of NaOH used to the first equivalence point.

Trial 2-25 mL of decarbonated Pepsi, 0.01 M NaOH used for the titration, and 8.5 mL of NaOH used to the first equivalence point.

Trial 3-25 mL of decarbonated Coke, 0.01 M NaOH used for the titration, and 14.8 mL of NaOH used to the first equivalence point.

Trial 4-25 mL of decarbonated Coke, 0.01 M NaOH used for the titration, and 16 mL of NaOH used to the first equivalence point.

VIII. Results:

The moles of H3PO4 present in the cola sample:

Trial 1-- mol = M(L)

mol = (0.01 M)(0.008 L)

mol = 8 x 10-5 H3PO4 moles

Trial 2-- mol = (0.01 M)(0.0085 L)

mol = 8.5 x 10-5 H3PO4 moles

Trial 3-mol = (0.01 M)(0.0148 L)

mol = 1.48 x 10-4 H3PO4 moles

Trial 4-mol = (0.01 M)(0.016 L)

mol = 1.6 x 10-4 H3PO4 moles

The molar concentration of H3PO4 in the cola sample:

Trial 1-M = moles / L

M = 8 x 10-5 H3PO4 moles / 0.025 L

M = 3.2 x 10-3 mol/L H3PO4

Trial 2-M = 8.5 x 10-5 H3PO4 moles / 0.025 L

M = 3.4 x 10-3 mol/L H3PO4

Trial 3-M = 1.48 x 10-4 H3PO4 moles / 0.025 L

M = 5.92 x 10-3 mol/L H3PO4

Trial 4-M = 1.6 x 10-4 H3PO4 moles / 0.025 L

M = 6.4 x 10-3 mol/L H3PO4

For the first trial, we hit our first equivalence point between 6 and 8 pH in approximately 100 seconds(See graph # 1). The second trial, pH between 6 and 8 and in approximately 50 seconds(See graph # 2). The third, pH between 4 and 5 in about 50 seconds(See graph # 3). And our last one, pH between 4 and 5 and about 25 seconds(See graph # 4).

IX. Conclusions:

For the titration of the Pepsi, we came to the conclusion that it had 0.00008 to 0.000085 moles per liter of acid in Pepsi and had a Molarity of 0.0032 to 0.0034 of acid. For the Coke, it had 0.000148 to 0.00016 moles per liter of acid and had a Molarity of 0.00592 to 0.0064 of acid. From this statement, you can see that the Pepsi has more acid (H3PO4) than the Coke product does. Thus the Coke will erode other substances quicker, like the enamel on your teeth, than would Pepsi. As you can tell by the graphs, our calculations may be off a bit. When titrating these substances, we ran the base right underneath the pH probe which made our graphs a little difficult to read.

X. Real World Applications:

In order for things to stay fresh on the shelves, we can things in highly acidic juices to keep them from spoiling. It takes much longer for things to spoil in such acidic environments. Also, chemists use this type of titration at the Cola plant when making cola products. They are like the ingredients to making cookies. Instead of 3 cups of flour, it calls for 1 cup of H3PO4.