A 35.00 mL solution of 0.2500 M #HF# is titrated with a standardized 0.1532 M solution of #NaOH# at 25 degrees C. What is the pH of the #HF# solution before titrant is added? For #HF#, the Ka = 6.8 x 10–4 . W

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Answer 1 · 2016-06-21T17:48:00

#1.88#

A quick way to do this is to use the the expression:

#pH=1/2(pK_a-loga)#

Where #a# is the concentration of the weak acid.

#K_a=6.8xx10^-4" " "mol/l"#

#:.pK_a=-log[6.8xx10^-4]=3.167#

#:.pH =1/2[3.167-log(0.25)]#

#pH=1/2[3.167-(-0.6)]=1.88#