Determination of Carbonate and Bicarbonate in Soda By Titration

1. Determination of Carbonate and Bicarbonate in Soda By Titration Rachel Jarrett Matt Marthaler

2. Purpose • In this experiment, we will determine the concentration of carbonate and bicarbonate species in different sodas using the technique of titration. A primary standard used in this experiment is NaOH for the direct titration of the diprotic acid. Color indicators which utilize changes in pH will be used to determine the presence of the different species of the acid.

3. Soda

4. Standardization of NaOH • Approximately 2 g of NaOH(s) pellets were placed in a 500mL volumetric flask and diluted to the mark with distilled water to make an approximate 0.1M solution. • Approximately 0.51g of KHP was weighed for three different samples for standardization of the base. • The KHP was dissolved in 25 mL of water, phenolphthalein was added and the solution was titrated with NaOH. • The mL required to reach the endpoint were used to determine the concentration of the base; the individual calculations were averaged to determine molarity.

5. Titration from Carbonic Acid to Bicarbonate • 25 mL of each cold, fresh soda was measured in a graduated cylinder. • The sample was then placed in a beaker • Methyl orange indicator was added to the solution • The solution was titrated with NaOH until an approximate endpoint was reached

6. Methyl Orange • Color of this indicator changes from yellow to orange to red at pH between 3.1 and 4.4 • At a strong orange, all carbonic acid has turned into bicarbonate and indicates a pH around 3.7 • This color difference was difficult to determine

7. Titration from Bicarbonate to Carbonate • 25 mL of each cold, fresh soda was measured in a graduated cylinder. These samples were separate from the previous samples. • The sample was then placed in a beaker • Phenolphthalein indicator was added to the solution • The solution was titrated with NaOH until an endpoint was reached

8. Phenolphthalein • Color of this indicator changes from colorless in an acidic solution to pink/purple in a basic solution • At pink/purple, all bicarbonate has turned into carbonate

9. Standardization Data

10. Titration of Bicarbonate Using Methyl Orange

11. Titration of Carbonate Using Phenolphthalein

12. Percent Carbonate and Bicarbonate in Soda in a 20 oz Soda Bottle

13. Calculations for Standardization • Amount of NaOH Pellets 0.1 moles NaOHx 0.5 L x 39.997 g NaOH 1 L NaOH 1 mole NaOH = 1.999 g • Mass KHP 25mL x 1L x0.1mole NaOH x 1 mole KHP x 204.221g KHP 1000mL 1L 1 mole NaOH 1 mole KHP =0.5106 g • MolarityNaOH 0.5106g KHP x 1 mole KHP x 1mole NaOH x 1 x1000mL 204.221g 1mole KHP 26.64mL 1L =0.09345 M

14. Calculations for Carbonate and Bicarbonate • Bicarbonate (Sprite): 0.0888 moles NaOHx 0.67 mL x 1 L x 1 mole HCO3-x x1,000 mL L 1,000 mL 1mole NaOH 25 mL L = 0.002380 moles HCO3- / L • Carbonate (Sprite): 0.0888 moles NaOHx 17.41 mLx 2 moles CO32-x_ L 1 mole NaOH 25 mL = 0.1237 moles CO32- / L

15. Percent Carbonate and Bicarbonate in a 20 oz Bottle • Bicarbonate (Sprite): average moles x 61 g bicarbonate x 591 mL mole 25 mL = 0.0823854 g bicarbonate x 100 591 g Sprite = 0.01394% • Carbonate (Sprite): average moles x 60 g carbonate x 591 mL mole 25 mL = 4.244562 g carbonate x 100 591 g Sprite = 0.7318%

16. Conclusion Our experiment can not be considered entirely accurate, but it was not a failure. Some of the inaccuracies come from: • Re-standardization of more NaOH due to a short supply of the solution in the middle of the experiment • Inconsistencies due to the gradual color change of methyl orange. We did not know when to stop the titration since the color of orange is difficult to read consistently. • Due to the carbonation in soda, a graduated cylinder was used to measure the volume of soda since the bubbles made it impossible to use a pipet. • The density of water was used to calculate the percent carbonate and bicarbonate since there are not published values for the density of the different sodas • When measuring the acidity of these beverages, other acids present in the soda such as citric acid can distort the perception of carbonic acid and change results. Regardless of the possible reasons for error, the standard deviations of this experiment were reasonable, so precision was achieved within the calculations. The amount of carbonate and bicarbonate were determined, therefore, the experiment was successful and error can be acknowledged.