Gen chem question

[151AND8TH]

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How many ml of 3M H2SO4 are required to neutralize 30 ml of 4M NaOH?

I thought the answer would be 40 ml. but its 20 ml. (due to the 1:2 ratio after the equation is balanced... i guess)... anyway, I still dont understand the concept on why the volume of H2SO4 had to be cut in half. Can someone please elaborate?

 

[Doctor PJ]

2 hydrogen atoms there make the solution stronger. Remember to use Normality x Volume here. 3M x 2 Hydrogens =6N x V = 120. V = 20ml

It takes a smaller volume or amount to dissolve something that has a lower moles/solution than the 6N.

 

[151AND8TH]

perfect! thank you! .. normaly, when do you look for NORMALITY? becuase for this problem I obviously used m1v1=m2v2

 

[nt4reall]

H2SO4 + 2 NaOH --> Na2SO4 + 2 H2O

Find the mole number of NaOH = Molarity x Volume
= 4 M x 0.3 L = 0.12 mol
1 mol H2SO4 needs 2 mol NaOH ( the equation above )
Therefore , 0.12 mol of NaOH will need 0.06 mol H2SO4
The volume of H2SO4 = mole number/molarity
= 0.06 mol/3 M
= 0.02 L = 20 mL