BUFFERS AND TITRATION OF AN AMINO ACID Essay Example
- Category:Other
- Document type:Assignment
- Level:High School
- Page:1
- Words:306
AIM OF EXPERIMENT
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Proving the buffer capacity of [HPO42-] and [H2PO4—] through the employment of calibrated pH meter
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Using the pH values provided [a=5.9, b=6.9 and c=7.9], calculate the ratio of [H2PO4—] to [HPO42-] required in producing the buffer solutions.
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Take 0.1 M HPO42- and 0.1M H2PO4— Solutions of appropriate volumes and mix the two solutions to yield a total volume of 25ml for each buffer solutions.
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Use the calibrated pH meter, then measure and record the pH value of both solutions and compare with the pH value of distilled water (25ml).
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Then add 2.0ml of 0.1M NaOH in each buffer sample (25ml) then to the distilled water and thoroughly mix each tube.
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Once the alkali is added the pH of each solution is recorded.
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In the tabulation of the results, a column for pH change is included. Account for pH shift magnitude in reference to pH shift direction (away from or towards the pka value).
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Initial pH
pH after adding 2ml of
0.1M NaOH
Change in
Moving to or away from pka
RESULTS AND DISCUSSION
The overall equation for the reaction in as follows:
H2PO4— (aq) H+ (aq) + HPO42- (aq)
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This keeps the system at pH of around 7.4, since it lies between 7.35 and 7.45.
The dissociation of H2PO4— in water gives the following equation:
H 2PO4¯ + H2O HPO42- + H3O+
The equilibrium for the above reaction is given by the following reaction:
[HPO42-] [H3O+]
= 2.303 C.
(Ka + [H3O+]) 2
βKa x H3O+
pKa= pH_therefore_ Ka = [H3O+]
ax. Buffer capacity= 2.303 C
([H3O+] + [H3O+]) 2
M[H3O+] x [H3O+]
Max. Buffer capacity= 2.303 C
[H3O+] 2
C= Morality = 0.1+0.1= 0.2M
Max. Buffer capacity (β) = 2.303 x 0.2 x ¼
The buffer capacity is 0.1152.
CONCLUSION
The buffer capacity obtained above (0.1152) depends on the sum of buffer concentration.