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. 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

initially

mol of acid = MV = 0.3*0.250 = 0.075

mol of formate= MV = 0.2*0.25 = 0.05

now, after adding

mol fo NaOH = mass/MW = 2.75/40 = 0.06875

there is reaction, acetic acid forms acetate

mol of acid = 0.075-0.06875 = 0.00625

mol of formate = 0.05+0.06875= 0.11875

now

pH= pKa + log(formic/acid)

pKa = -log(ka) = -log(1.8*10^-4) = 3.75

pH= 3.75+ log(0.11875/0.00625)

pH=5.02875

since pH >4.5m, there will not be living bacteria

Related Questions

Navigate

• Browse (All)
• Browse S
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.