Determination of CO2 in soft drink


Principle:
Co2 gives the beverage its sparkle and tangy taste and prevents spoilage while it has not been conclusively proved that carbonation offers a direct medical benefit , carbonated beverages are used to alleviate postoperative nausea when no other food can be tolerated as well as to be ensure adequate liquid intake.
Co2 is supplied to soft drink manufacture in either solid form (dry ice) or liquid form maintained under approximately 1200psi pressure in heavy steel container. Light weight steel containers are used when the liquid co2 is held under refrigeration. In that case, the internal pressure is about 325psi. Carbonation is affected by chilling the liquid and cascading it in thin layers over the series of plates in an enclosure containing co2 gas under pressure. The amount of gas water will absorb increases as the pressure is increased and temperature is decreased.


                                                                   
Apparatus and chemicals:
Burette, stand, beaker 100ml, 50ml, 0.1M NaOH, 0.05M oxalic acid, phenolphthalein, pippete, glass rod etc
CHEMICAL EQUCATION:
(COOH)2 + 2NaOH   à   Na2C2O4 + H2O
H2CO3 + NaOH       à    NaHCO3 + H2O
A)  STANDARIZATION OF NaOH BY USING OXALLIC ACID.
PROCEDURE:
(1)             10ml of 0.1M NaOH has been taken in the conical flask.
(2) Followed by 2 to 3 drops of phenolphthalein as an indicator.
(3) 0.05M oxalic acid has been taken in the burrette.
(4) Required amount of the oxalic acid to neutralize the NaOH has been determined.
(5) Same process has been repeated for three times and mean volume was determined.
(6) The initial pink colour of NaOH has been converted into colourless on titrating it againt standard oxalic acid solution taken in the burette.
(7) Hence, mean volume was noted. 



OBSERVATIONS AND CALCULATION:
Amount of the sample = 10ml
Molarity of NaOH used = ?M
Mean volume of oxalic acid = ?
Sr no
Initial volume
Final volume
Volume of oxalic acid used
01
0.0ml
10.0ml
10.0ml
02
10.0ml
20.0ml
10.0ml
03
20.0ml
30.0ml
10.0ml
               Mean volume = 10+10+10/3= 10
1000ml of oxalic acid has no of moles = 0.05mol
1ml of  oxalic acid has no of moles     = 0.05/1000
10ml of the oxalic acid has no of moles = 0.05/1000x10=0.0005mol

From equation, we have
(COOH)2 + 2NaOH à Na2C2O4 + H2O
No of moles of oxalic acid = no of moles of NaOH
   0.0005 mol                      =    2x0.0005mol
                                           =       0.001mol
10ml of NaOH contain no of moles = 0.001mol
1ml of NaOH contain no of moles   = 0.001/10
1000ml of NaOH has no of moles   = 0.001/10x1000=0.1M
So molarity of NaOH = 0.1M
(b)Determination of co2 in soft drinks
Procedure:
(1) 20ml of the soft drink has been taken in a conical flask.
(2) Followed by 2 to 3 drops of phenolphthalein as an indicator.
(3) Reaction mixture has been titrated with 0.1M NaOH solution.
(4) 0.1M NaOH has been taken in the bRurette.
(5) Volume of the NaOH required to neutralize H2CO3 has been determined.  
(6) The colorless solution of soft drink has been converted into pink on the end of the titration.
(7) Same process has been repeated for three times and means volume has been noted.
OBSERVATIONS AND CALCULATIONS
Amount of the sample = 20ml
Molarity of NaOH used = 0.1M
Volume of the NaOH used =?
sr No
Initial volume
Final volume 
Volume of the NaOH used

01
0.0ml
8.7ml
8.7ml
02
8.7ml
17.2ml
8.5ml
03
17.2ml
25.8ml
8.6ml
 Mean= 8.7+8.5+8.6/3=8.6ml
1000ml of NaOH has no of moles = 0.1mol
1ml of NaOH has no of moles     = 0.1/1000
8.6ml of NaOH has no of moles = 0.1/1000x8.6= 0.00086mol

From equcation, we have
H2CO3 + NaOH à NaHCO3 + H2O
No of moles of NaOH = no of moles of CO2/H2CO3
0.00086mol = 0.00086mol

So
20ml of the soft drink contains no of moles of co2 = 0.00086mol
1ml of the soft drink contain no of moles of co2 = 0.00086/20
1000ml of soft drink contains no of moles of co2 = 0.00086/20x1000=0.043mol
Now
Strength in g/L = Molarity x molecular weight
= 0.043 x 44 = 1.892g/L
= 1.892 x 1000mg/L
= 1892mg/L
RESULT:

Hence the given soft drink sample contains 1892mg/L of CO2.