when a 28.4 mL sample of a 0.308 M aqueous nitrous acid solution is titrated wit
ID: 556230 • Letter: W
Question
when a 28.4 mL sample of a 0.308 M aqueous nitrous acid solution is titrated with a 0.477 M aqueous barium hydroxide solution 1. what is the ph at the midpoint in the titration 2. what is the ph at the equivalence point of the titration When a 28.4 mL. sample of a 0.308 M aqueous nitrous acid solution is titrated with a 0.477 M aqueous barium hydroxide solution, (1) What is the pH at the midpoint in the titration? (2) what is the pH at the equivalence point of the titration? t (3) What is the pH after 13.8 mL of barium hydroxide have been added? [ ]Explanation / Answer
HNO2 is a weak acid , Ba(OH)2 is a strong base.
1. at mid point pH = pka of HNO2 = 3.15
2. pH at equivalence point = 7+1/2(pka+logC)
c = CONCENTRATION OF SALT = 28.4*0.308/(28.4+36.67) = 0.134 M
pH = 7+1/2(3.15+log0.134) = 8.14
3. no of mol Ba(OH)2 ADDED = 13.8*0.477 = 6.6 mmol
no of mol of HNO2 taken = 28.4*0.308 = 8.75 mmol
2 mol HNO2 = 1 mol Ba(oh)2
concentration of excess Ba(OH)2 = (6.6 -(8.75/2))/(13.8+28.4) = 0.053 M
ph = 14 - (-log(OH-))
= 14 - (-log0.053*2)
= 13
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