TF: Name: Prelab 1. You dissolve 0.725 g of water HC1. The titration curve is sh
ID: 1025721 • Letter: T
Question
TF: Name: Prelab 1. You dissolve 0.725 g of water HC1. The titration curve is shown below. Using the information from this titration curve, determine the following: 12 10 0S 10520 mL of 0.500 M HCI added a) The first acid dissociation constant Kai and second acid dissociation constant Ka: for the conjugate acid to this weak base. Briefly state how you arrived at your answer Ka(H2A)- b) The molar mass of the base. Molar Mass- 2. What features of the above curve indicate that we have titrated a weak base? Experiment 12Explanation / Answer
a)
pH at first 1/2 equivalence point = pKb1
From the graph,
pH at first 1/2 equivalence point = 8.1
pKa2 = 14 - pKb1 = 14 - 8.1 = 5.9
pKa1 = -logKa1 = 5.9
Ka1 = 1.26 x 10^-6
pH at second 1/2 equivalence point = pKb2
From the graph,
pH at second 1/2 equivalence point = 4.8
pKa1 = 14 - pKb2 = 14 - 4.8 = 9.2
pKa1 = -logKa1 = 9.2
Ka1 = 6.31 x 10^-10
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