1. The first step of the model requires the preparation of a phosphate buffer wh
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1. The first step of the model requires the preparation of a phosphate buffer whose initial pH o t are added to 1.0 I 7.45 will drop by only 0.2 pH units when 0.020 moles of H buffer. Using the VL tutorial as a guide, calculate what( H.POeak acid) and THPO (the conjugate base) should be in the phosphate buffer to meet these requirements. You will be making only 100.0 mL of phosphate buffer. Calculate the number of moles of You will be making only 1000 mL of phosphate buffer. Calculate the number of moles of the two buffer components required In the lab you will be provided with stock solutions of 0.50 M H2PO4 and 1.0 M NaOH with which to prepare your phosphate buffer. The NaOH is used to prepare th HPO42 from its weak acid H2PO. Use the VL tutorial as a guide to calculate the exact number of mL of the weak acid required to create your buffer. This calculation must be done before you come to the lab. What volume did you calculate? (DI) You will use this data to immediately begin preparing your buffer solution once you are in the lab. You will not have time to finish the experiment if you have not already done this calculation! he NaOH is used to prepare the conjugate baseExplanation / Answer
Desired pH of the buffer = 7.45
Using Henderson-Hesselbach equation:
pH = pKa + log [base]/[acid]
7.45 = 7.2 + log[HPO4^2-]/[H2PO4^-]
[HPO4^2]/[H2PO4^-] = 1.8
Given H2PO4^ stock solution = 0.5M
therefore: HPO4^2- = 1.8 * 0.5 = 0.9M
For a 100ml buffer:
# moles of acid [H2PO4^] = 0.5 * 0.1 = 0.05 moles
# moles of base [HPO4^2] = 0.9 * 0.1 = 0.09 moles
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