Respuesta :
A) 0.60 is the pH of the HF solution before titrant is added.
b) 66.38 ml is the amount of titrant required to reach equivalence point.
c)9.1 is the pH at 0.50 mL before the equivalence point.
d)9.1 is the pH at the equivalence point.
e) 8.9 is the pH at 0.50 mL after the equivalence point.
Explanation:
Data given:
a) volume of HF = 35 ml
concentration of HF = 0.25 M
pka of HF = 3.14
pH = ?
HF is an strong acid so it ionizes completely thus hydronium ion concentration is 0.25 M
pH = - log [H3O+]
pH = - log [ 0.25]
= - [- 0.60]
pH = 0.60
b) To calculate volume of titrant, formula used is
MacidVacid = MbaseVbase
volume of acid = 35ml
molarity of acid = 0.25
molarity of titrant base = 0.1318
volume of base =?
putting values in the equation
35 x 0.25 = Vbase x 0.1318
V base = [tex]\frac{35 x 0.25}{0.1318}[/tex]
= 66.38 ml
c) pH at 0.50 ml before equivalence point
molarity of NaF is 0.25 before 0.50 ml equivalence point.
molarity of NaF = [tex]\frac{MaVa}{Va+Vb-0.50}[/tex]
= [tex]\frac{0.25 x 35}{35+ 66.3-0.50}[/tex]
[NaF] = 0.086
pH = 7+[tex]\frac{1}2}[/tex].(pKa -log [NaF])
pH = 9.1
d) pH at equivalence point
molarity of NaF = [tex]\frac{MaVa}{Va+Vb}[/tex]
= [tex]\frac{8.75}{35 +66.38}[/tex]
molarity = 0.086
pH = 7+[tex]\frac{1}2}[/tex].(pKa -log [NaF])
= 7 + O.5 (3.14 + 1.06)
= 7 + 2.1
pH = 9.1
e) pH at 0.50 ml after equivalence point is
molarity of NaF is calculated by:
molarity of NaF = [tex]\frac{MaVa}{Va+Vb+0.50}[/tex]
= 0.172
pH = 7+[tex]\frac{1}2}[/tex].(pKa -log [NaF])
pH = 8.9
