DETERMINATION OF Pka FOR PARA-NITROPHENOL - Computer Programming

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Friday, April 1, 2011

DETERMINATION OF Pka FOR PARA-NITROPHENOL


DETERMINATION OF Pka FOR PARA-NITROPHENOL
Aim:
    To determine the Pka of P-Nitrophenol solution.
Principle:
The undissociated form of P-Nitrophenol in acidic medium does not absorbs radiant energy in visible region, while quinanoid in alkaline medium absorbs strongly. The pH at which 50% ionization or gives half of pH at which 50% ionization or gives half of the absorbance value obtained in alkaline solution assuming 100% ionization of P-Nitrophenol.
Chemicals required:
1.      Phosphate buffer ( 0.2M)
2.      Carbonate-Bicarbonate buffer (0.1)
3.      Citrate buffer(0.05)
4.      P-Nitrophenol
Apparatus required:
1.      Spectrophotometer/ colorimeter
2.      Glass cuvettes 
3.      Standard flasks, etc
Preparation of buffer solution:-
Buffer 1: (Citrate Buffer)
A). Citric acid – 0.05Mà 210.14g/l (10.5g/là0.05M)
B). Sodium citrate- 0.05Mà 294.00g/l (14.7à0.05M)
     A-145ml + B-355= 500ml (make up to 500ml) + 0.139gm (2x 10-3)
P-Nitrophenol is mixed with this buffer solution.
Buffer 2: (Phosphate Buffer)
A). KOH- 0.2Mà 56.11g/l (11.22g/là0.2M)
B). KH2PO4- 0.2Mà 136.09g/l (27.22g/là 0.2M)
A-65ml + B- 250ml + water -185ml (make up to 500ml) + 0.139gm (2x 10-3) 
P-Nitrophenol is mixed with this buffer solution.
Buffer 3: (Phosphate Buffer)
A).KOH- 0.2M à 56.11g/l (11.2g/là0.2M)
B).KH2PO4- 0.2Mà 136.09g/l (27.22g/là 0.2M)
A-120ml + B- 250ml + water -130ml (make up to 500ml) + 0.139gm (2x 10-3) 
P-Nitrophenol is mixed with this buffer solution.
Buffer 4: (Phosphate Buffer)
A). KOH- 0.2M à 56.11g/l (11.2g/là0.2M)
B). KH2PO4- 0.2Mà 136.09g/l (27.22g/là 0.2M)
A-200ml + B- 250ml + water -50ml (make up to 500ml)+ 0.139gm (2x 10-3) 
P-Nitrophenol is mixed with this buffer solution.
Buffer 5: (Carbonate Buffer)
A).Sodium carbonate -0.1Mà 10.599g/l (10.6g/là0.1M)
B). Sodium bicarbonate -0.1M à 84g/l (8.4g/là0.1M)
 A-5ml + B- 465ml (make up to 500ml) + 0.139gm (2x 10-3) P-Nitrophenol is mixed with this buffer solution.
Procedure:
1.      The above prepared P-Nitrophenol obtaining buffer solutions (Citrate, Phosphate, Carbonate).
2.      Absorbances were recorded at 430nm.
3.      A graph was plotted, absorbance against pH of the solutions.
4.      The pH corresponding to the maximum absorbance value was divided by two to give the Pka – value of P-Nitrophenol.
Result:
      The Pka value of P-Nitrophenol is fount to be………………










Determination of Pka value for P-Nitrophenol solution
Buffer
Ph
Absorbance 430nm
Citrate


Phosphate I


Phosphate I


Phosphate I


Phosphate I



Calculations:
From the graph maximum pH=
Pka value of P-Nitrophenol = 


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