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You need to produce a buffer with pH = 4.33 by dissolving a weighted amount of...

You need to produce a buffer with pH = 4.33 by dissolving a weighted amount of sodium lactate in 500-mL of 0.65-M lactic acid

(a) What mass of sodium lactate is required? (sodium lactate has a molar mass of 112.06 g/mol)

(b) What is the resulting pH if 45-mL of 0.18-M NaOH is added to 250 mL your buffer?

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Answer #1

a)

pKa = 3.86

pH = 4.33

pH = pKa + log [salt / acid]

4.33 = 3.86 + log [sodium lactate / lactic acid]

[sodium lactate / lactic acid] = 2.95

sodium lactate / 0.325 = 2.95

moles of sodium lactate = 0.9588

mass of sodium lactate = 107.4 g

b)

moles of NaOH added = 45 x 0.18 / 1000 = 0.0081

moles of lactic acid = 0.1625

moles of sodium lactate = 0.959

pH = 3.86 + log [0.959 + 0.0081 / 0.1625 - 0.0081]

     = 4.66

pH = 4.66

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