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Calculate the pOH of a solution that is 0.448 M NH 2 NH 2 and 0.187 M NH 2 NH 3

ID: 495214 • Letter: C

Question

Calculate the pOH of a solution that is 0.448 M NH2NH2and 0.187 M NH2NH3Cl. Kbof NH2NH2is 1.7 x 10-6?

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Explanation / Answer

1)

pKb = -log Kb = -log (1.7 x 10-6)

       = 5.77

pOH = pKb + log [NH2NH3Cl /NH2NH2 ]

        = 5.77 + log (0.187 / 0.448)

pOH = 5.39

2)

Calculate the pH when 0.89 g of NaF is added to 44 mL of 0.50 M HF. Ignore any changes in volume. The Ka value for HF is 3.5 x 10-4?

pKa = 3.46

moles of NaF = 0.89 / 42 = 0.02119

moles of HF = 44 x 0.50 / 1000 = 0.022

pH = pKa + log [NaF / HF]

     = 3.46 + log [0.02119 / 0.022]

pH = 3.44

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