How Do You Calculate the Volume of NaOH Needed to Neutralize an Acidic Solution?

[pikkie]

can some one help me withe this?
i want to neutralise a 400m3 of unknown solutions in pH 2 with sodium hydroxide. homework can i calculate the volume of alkaline needed? please help me!

 

[Hootenanny]

HINT: Knowing the pH you can determine the hydrogen ion concentration.

 

[Borek]

I hate such questions. You can't calculate anything without assuming that you have a solution of strong acid. Then (and only then) Hootenanny hint will work.

 

[pikkie]

Thank you

Thank you! I solve it already by assuming it's a strong acid and got the answer. Thank you!

 

[Hootenanny]

I hate such questions. You can't calculate anything without assuming that you have a solution of strong acid. Then (and only then) Hootenanny hint will work.


Borek

Ahh, yes thank you Borek. I had forgotten about week acids (never liked them anyway ) As Borek said, I think one would have to assume that the acid in question is a strong acid as no dissociation constant is given.

 

[pikkie]

Problems Again

I solved for the heat of neutralization already, I thought, but now, I got the final temperature after reaction is 121.75 oC which I think is too big.

I start with initial pH = 2 and final the conc H+ = 10^-(pH=2) then I find the mole by multipling the conc with the tank volume (400m3), the I find the mass by multiply it with MW.

To neutralise 1 mole of H+, I need 1 mole of OH-, so I balance the mole of OH- needed with the mole of H+ I calculated justnow. The I got the mass and volume of NaOH needed to neutralize the pH 2.

The heat of neutralization is -55.9 kJ/mol. The energy balance is (m.Cp.del_T)in = (m.del_H) + (m.Cp.del_T)out

But since i use the initial temperature and reference temperature both also 25 oC, so the (m.Cp.del_T)in is cancelled. What left is only
-(m.del_H) = (m.Cp.del_T)out

The part that confused me here is what m should I use for these m.del_H and m.Cp.del_T. I obtained the answer stated ealier (121.75 oC) by using the mass for m.del_H is the mass of water produced and the mass for m.Cp.del_H is the mass of the total mass of NaOH+H2SO4 that reacted. Is this correct? If yes, is the temperature I got reasonable? If not, what's my mistake?