Determination of carbon dioxide in soft drink

Determination of carbon dioxide in soft drink

Introduction /principal:

Carbon dioxide is a major component of atmospheric gases and a by-product of respiration.  It is present in groundwaters. Usually, the concentration of carbon dioxide is below 10 milligrams per liter. However higher concentrations are often found. Higher concentrations of carbon dioxide are harmful to humans when dissolved in the blood. Carbon dioxide is dissolved in soft drinks to give a fizzy nature and make it acidic. Carbonic acid is synthesized when carbon dioxide is dissolved in water.

Theory:

The analysis of carbon dioxide involves titration using a phenolphthalein indicator and a standard sodium hydroxide solution. The assumption is made that strong mineral acids are absent in such low concentrations as to not significantly alter the results. Care must be taken to minimize the loss of carbon dioxide from the sample through aeration and changes in temperature. Sodium hydroxide reacts with the carbon dioxide in the form of carbonic acid in 2 steps.  The first step is hydrogen carbonate and is formed which then reacts with additional sodium hydroxide to form carbonate ion.

 

CO2 2 + H2O   →   H2CO3

H2CO3 + NaOH → NaHCO3 + H2O

NaHCO3 + NaOH → Na2CO3 + H2O

 

The conversion to bicarbonate ion is complete at a pH 8.3 and an indicator of an endpoint of about 8.3 must be used. Phenolphthalein is there for an acceptable indicator. The sodium hydroxide should be pure and free of carbonates that will change the results with the titration

Apparatus and Equipment:

  • Erlenmeyer flask
  • Pipette
  • Beaker
  • Measuring cylinder
  • Burette
  • Weighing balance
  • Volumetric flask

Chemicals and Reagents:

  • 1M NaOH (dissolve 40 gram of sodium hydroxide
  • Phenolphthalein indicator
  • Soft drink

Determination of carbon dioxide in soft drink

Procedure:

  • 40 ml of 0.1 M sodium hydroxide is taken in a small clean beaker
  • Rinse burette with about digital water and drain into the sink
  • Then rinse drain the period bed about 5 ml of sodium hydroxide solution
  • Some of the solutions are flowed through the tip to remove air bubbles
  • Fill the burette with a standard solution of sodium hydroxide up to the 0.0 mL mark
  • Always use a clean and clear burette
  • A graduate cylinder is used to add exactly 20 ml of sample to a clean 125 ml Erlenmeyer flask at room temperature
  • Use a clean stirring rod to remove for shaking to extra carbon dioxide
  • 2-3 drops of indicator phenolphthalein solution are added to the flask
  • Now use titration technique simply acid-base titration
  • Titrate the sample solution carefully with sodium hydroxide solution with gently shaking the flask to mix the solution
  • When pink color is obtained after shaking, this is called the endpoint of the titration
  • Note the volume of standard solution used
  • Similarly, three readings were taken to minimize the error

Observations and calculations:

 

Volume of soda taken V1 = 10 mL

Molarity of NaOH M2= 0.1 M

 

Sr No Volume of NaOH used V2 mL  Volume of sample mL
1                 15.4            10
2                 16.1            10
3                 15.5            10

 

Mean volume of NaOH = 15.6 mL

                              Soft drink = NaOH

                                    M1 V1 = M2 V2

                                           M1= M2 V2/ V1

                                           M1 = 0.1 x 15.6/10

                                          M1 =0.15 M

Amount of carbon dioxide in soft drink= Molarity x    

                                                                       M weight

                                                                   = 0.15 x 44

                                                                    = 6.6 g/L

Result:

The given soft drink contains 6.6 gram of carbon dioxide per liter

Precautions:

  • Always use clean glassware and rinse it with distilled water before the use
  • Always use a small piece of white paper under the flask to judge the change in color correctly
  • Don’t try to drink the soft drink given to you for the experiment
  • Always come to the laboratory with proper attire

Determination of carbon dioxide in soft drink

 

 

 

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