Calculate the pH for a buffer solution prepared by mixing 100.0mL of 0.10M HF and 200.0mL of 0.10M KF

Question

A. 2.82

B. 2.96

C. 3.32

D. 3.44

E. 3.53

Answer 1

This is a buffer system, so you can use the Henderson Hasselbalch equation, but first you must know or look up the Ka or pKa of HF.  The value I found is Ka = 6.6x10-4 and pKa = 3.18.

Henderson Hasselbalch:

pH = pKa + log [salt]//[acid]

[salt]: (200 ml)(0.1 M) = (300 ml)(x M) and x = 0.0667 M

[acid]: (100 ml)(0.1 M) = (300 ml)(x M) and x = 0.0333 M

 

pH = 3.18 + log (0.0667/0.0333)

pH = 3.18 + 0.301

pH = 3.48

Can't tell if the correct answer is D or E because it will depend on the value of pKa that was used.