Acid & Base by Topscore

[jessica22]

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I thought I am okay with Acid & Base, but appearantly not. Can someone pls help me out with this problem? THANKS!

What volume of HCl was added if 20 mL of NaOH is titrated with 1 M HCl to produce a pH=2

a) 10.2 mL
b) 20.2 mL
c) 30.4 mL
d) 35.5 mL
e) none of the above

 

[dat_student]

I thought I am okay with Acid & Base, but appearantly not. Can someone pls help me out with this problem? THANKS!

What volume of HCl was added if 20 mL of NaOH is titrated with 1 M HCl to produce a pH=2

a) 10.2 mL
b) 20.2 mL
c) 30.4 mL
d) 35.5 mL
e) none of the above

Assume:
Vh = Volume of HCl

(Vh - 20)(1 M)
_____________ = 10^-2
Vh + 20

0.99 Vh = 20.2

Vh = 20.404 >> so, none of the above

Let's see if I have the right number:

moles of H+
___________
total volumes

(20.404 - 20) * 1 moles/liter
_________________________ =
40.404 (total volume)

0.404 milli-moles
______________ = 10^-2 which is pH = 2 🙂
40.404 milli-liters