Calculating Titrant pH Without Henderson Hasselbach Equation

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SUMMARY

This discussion focuses on calculating the pH of a titration involving nitrous acid (HNO2) as the analyte and sodium hydroxide (NaOH) as the titrant, without using the Henderson-Hasselbalch equation. The specific concentrations are [HNO2] = 0.10 mol/dm³ and [NaOH] = 0.125 mol/dm³, with volumes of 25 ml and 20 ml, respectively. The pH after adding 10 ml of the titrant is confirmed to be 4.3. The relevant equilibrium constant for nitrous acid is provided as Ka = 5.1 x 10-4.

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  • Understanding of weak acid and strong base titration principles
  • Familiarity with the concept of acidity constant (Ka)
  • Knowledge of concentration calculations in titrations
  • Ability to solve quadratic equations for pH calculations
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  • Review the calculation of pH in weak acid-strong base titrations
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  • Explore alternative methods for pH calculation without the Henderson-Hasselbalch equation
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Chemistry students, laboratory technicians, and educators involved in acid-base titration experiments and calculations.

navaq
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Titrant

[HNO2]= 0.10 mol/dm3
v= 25ml = 0.025 dm3

+

Analyte

[NaOH]= 0.125 mol/dm3
v= 20ml = 0.02 dm3

Question is: What is the ph after adding a volume 10ml of titrant?
I know the answer is ph= 4,3

I'm not allowed to use Henderson Hasselbach equation.
This is the only type of titration ph calculation i don't know how to do. When you add a certain volume of the titrant and one of them not being strong (the acid in this case).

Hope you can help me with the calculation or at least the steps so that I can try it and confirm.
Thanks
 
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Navaq,

There is a relatively simple form of equation to use which you can find in this board and in the other homework board, buried in some of the messages; I knew the form very well a few days ago but now forgot exactly how it goes. also easy to use...
without my going back to rederive it, the equation is (you'll need to recheck):
Ka = [H][Fs + H - OH]/(Fa - H + OH)

Manage your concentration calculations carefully; rearrange to the equational form you need, quadratic solution for H; Fs means formality of salt, Fa means formality of the weak acid.

One problem in your exercise description: Would your ANALYTE be the HNO2 (nitrous acid, the weak acid), and the TITRANT be the sodium hydroxide?
 
One problem in your exercise description: Would your ANALYTE be the HNO2 (nitrous acid, the weak acid), and the TITRANT be the sodium hydroxide?

Yes, it really is. Ka (nitrous acid) = 5,1 x 10^(-4)
 

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