Some one help me on this acid-base titration

[lalaboi]

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This is from topscore and I'm confused on how to solve it.
What volume of HCL was added if 20mL of 1M NaOH is titrated with 1M HCl to produce a pH=2? Thanks in advance! 😀

 

[aranjuez]

This one's been solved a ton of times on the forums, but I'll post it again for you:

First, N1V1 = N2V2... (1N)x=(1N)(20mL)... so x = 20mL of HCl to neutralize it... now we have to get it down to pH of 2... which means the concentration of H+ has to be 0.01 (pH = 2 ---> [H+]= 10^-2 = 0.01)

Use M1V1 = M2V2
(1M)(x) = (0.01)(40+x)
Solve for x... you get 0.4

So all in all... 20+0.4 = 20.4

And there's your answer.

aranjuez