[lenakii]

Hi!!
Can you help me solve a mystery?
I was trying to neutralise a 10% H2SO4 solution (I believe that is 1M concentration), with a 1M NaOH solution and I found  out that I needed 3 parts of NaoH for 1 part H2SO4 to reach pH=7.
What did I do wrong?

[Arkcon]

Theoretically, equal volumes of equal normalities (I've switched units there, did you see, and do you know why?) of a strong acid and base will neutralize each other.  So, something mist be wrong.

How do you determine the concentration of sulfuric acid to be 10%?  What actual molarity is that?  What actual normality is that?  How do you determine molarity of NaOH (and why did I not mention the normality of NaOH?)  For that matter, how do you determine pH?

[lenakii]

ok a lot of questions, lets see if I can answer them all.
you used normality because H2SO4 has 2 hydrogens (I don't know how is it called in english).
The H2SO4 was prepared by diluting 10ml H2SO4 95-97% to 100ml H2O.
For the NaOH solution I first diluted a 4M solution that I had ready and then I prepared one by diluting 4gr pellets to 100ml H2O
For the pH determination I used pH papers and a pH electrode

[Borek]

The H2SO4 was prepared by diluting 10ml H2SO4 95-97% to 100ml H2O.

Such a procedure doesn't yield 1 M solution, obtained acid concentration is substantially higher.

[DrCMS]

The H2SO4 was prepared by diluting 10ml H2SO4 95-97% to 100ml H2O.
For the NaOH solution I first diluted a 4M solution that I had ready and then I prepared one by diluting 4gr pellets to 100ml H2O

As Borek has already pointed out due to the density of the concentrated sulphuric acid you used the final solution is higher than 1M. 

The NaOH solution you prepared was also likely to be less than 1M because the pellets were likely to be less than 100% NaOH.