Hydrogen Phosphate Buffer Systems

1119 words 5 pages
Experiment 8: Hydrogen Phosphate Buffer Systems

Purpose The purpose of the lab was to create a buffer solution and observe the capacity of the phosphate buffer system. Also, the experiment was meant to provide experience with the calculations and mathematics involved in creating the buffer solution. Finally, the lab was designed to provide an insight and appreciation for the necessity and complexity of buffers in our physiology and in the environment.

Procedure No deviations were made from the procedure in the online lab manual. A hydrogen phosphate buffer at pH 7 was used. 60.97g of KH2PO4 (acid) and 20.42g of K2HPO4 (base) were weighed out for use.

25mL of DIH2O in 100mL beaker had pH = 7.40. After one drop of 0.50M
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pH = pKa + log([base + x]/[acid – x])

Preparing the Diluted Buffer:
2H2O(l) (and ) ((H3O)^+)(aq) + [OH]^- (aq)
Kw = [H3O^+] [OH^-] = 1.0x10^-14 at 25°C. pKw = 14.
[A] in water = Kw/[B]
[B] in water = Kw/[A]
Initial concentrations of acid and base in diluted buffer: divide the initial concentrations from the regular buffer solution by two because half of the amount is used (12.5mL) in 25mL of total solution. Initial [A] = 0.378M/2 = 0.189M. Initial [B] = 0.122M/2 = 0.061M.
The rest of the calculations were completed as with the regular buffer.

Conclusion A hydrogen phosphate buffer system was used because phosphoric acid dissolves into dihydrogen phosphate, which works well as a buffer, due to its ability to either pick up another hydrogen and become phosphoric acid or to lose another hydrogen and become hydrogen phosphate. The pH of the prepared buffer solution was measured to be 6.15, and the initial acid and base concentrations were calculated to be 0.378M and 0.122M, respectively. The pH of diluted buffer solution (12.5mL buffer and 12.5mL DIH2O) was measured to be 6.37, and the initial concentrations of the acid and base were half of the concentrations (0.189M and 0.061M, respectively) of the regular buffer solution. When adding HCl to the diluted buffer, the pH dropped at a larger rate than when it was added to the regular buffer, and when NaOH was added, the pH


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