Determination of Carbonate and Bicarbonate in Soda By

TitrationRachel Jarrett

Matt Marthaler

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.

Purpose

Soda

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.

Standardization of NaOH

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

Titration from Carbonic Acid to Bicarbonate

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

Methyl Orange

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

Titration from Bicarbonate to Carbonate

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

Phenolphthalein

Standardization Data

Titration of Bicarbonate Using Methyl Orange

Titration of Carbonate Using Phenolphthalein

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

Amount of NaOH Pellets0.1 moles NaOH x 0.5 L x 39.997 g NaOH1 L NaOH 1 mole NaOH= 1.999 g

Mass KHP25mL x 1L x 0.1mole NaOH x 1 mole KHP x 204.221g KHP

1000mL 1L 1 mole NaOH 1 mole KHP=0.5106 g

Molarity NaOH 0.5106g KHP x 1 mole KHP x 1mole NaOH x 1 x

1000mL 204.221g 1mole KHP 26.64mL 1L

=0.09345 M

Calculations for Standardization

Bicarbonate (Sprite):0.0888 moles NaOH x 0.67 mL x 1 L x 1 mole HCO3

- x x 1,000 mL L 1,000 mL 1mole NaOH 25 mL L= 0.002380 moles HCO3

- / L Carbonate (Sprite):

0.0888 moles NaOH x 17.41 mL x 2 moles CO32- x _

L 1 mole NaOH 25 mL= 0.1237 moles CO3

2- / L

Calculations for Carbonate and Bicarbonate

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%

Percent Carbonate and Bicarbonate in a 20 oz Bottle

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.

Conclusion