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

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Discussion Overview

The discussion revolves around calculating the volume of sodium hydroxide (NaOH) required to neutralize an acidic solution with a pH of 2, specifically focusing on the assumptions necessary for such calculations and the implications of those assumptions on the results. The scope includes theoretical calculations, chemical reactions, and considerations of heat of neutralization.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks help to calculate the volume of NaOH needed for neutralization, given a 400m³ solution at pH 2.
  • Another participant suggests that knowing the pH allows for the determination of hydrogen ion concentration.
  • Some participants argue that calculations cannot proceed without assuming the acid is a strong acid, indicating that this assumption is critical for using the hint provided.
  • A participant mentions successfully solving the problem by assuming a strong acid, expressing gratitude for the hint.
  • One participant expresses confusion regarding the heat of neutralization calculation, questioning the mass to use in the energy balance equation and the reasonableness of the resulting temperature after the reaction.
  • The participant describes their method for calculating the moles of H+ and the corresponding moles of OH- needed for neutralization, as well as the heat of neutralization value used in their calculations.

Areas of Agreement / Disagreement

There is no consensus on the assumptions necessary for the calculations, particularly regarding whether the acid can be treated as a strong acid. Some participants agree on the need for this assumption, while others express differing views on the implications of weak acids. The discussion remains unresolved regarding the heat of neutralization and the appropriate mass to use in calculations.

Contextual Notes

Participants mention the lack of information on the dissociation constant of the acid, which affects the calculations. There is also uncertainty regarding the temperature results obtained from the energy balance calculations.

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

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

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