Suppose you\'re doing a research project with some thermophilic bacteria, which

Question

Suppose you're doing a research project with some thermophilic bacteria, which can live and even thrive in very hot, acidic environments. (Think "Yellowstone hotsprings.") You place a culture of these bacteria in 250.0 mL of a buffer solution containing 0.30 M formic acid (HCOOH, Ka = 1.8 10-4) and 0.20 M sodium formate (HCOONa) and let them stew at 80 degrees Celsius just before leaving the lab for lunch. While you're gone, a labmate, jealous of your good looks or your technical prowess or both and knowing this particular bacterium will die at a pH above 4.50, adds a scoop (about 2.75 g) of NaOH to your thermophilic brew. Will your bacteria survive? Figure it out by calculating the pH of the mixture.

Explanation / Answer

initial conditions:

mmol of acid = MV = 0.3*250 = 75

mmol of formate= MV = 0.2*250 = 50

after additino of:

mol of NaOH = mass/MW = 2.75/40 = 0.06875 mol = 68.75 mmol

now..

after reaction

formic acid left = 75-68.75 = 6.25

formate formed = 50+68.75 = 118.75

pH = pKa + log(formate/formica cid)

pH = 3.75+ log(118.75/6.25) = 5.0287

since pH > 4.5, then this will not survive

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