Titration of Nitrous Acid with Sodium Hydroxide

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Discussion Overview

The discussion revolves around the titration of nitrous acid (HNO2) with sodium hydroxide (NaOH), specifically focusing on determining the pH at the equivalence point. Participants explore the implications of weak acid-strong base titrations and the calculations involved in finding the new concentration at the equivalence point.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant questions how to determine the total volume at the equivalence point, indicating uncertainty about the amount titrated and its effect on concentration.
  • Another participant suggests revisiting the definition of the equivalence point to clarify the situation.
  • A participant confirms that the total volume at the equivalence point is the sum of the volumes of the titrant and the analyte, leading to a combined total of 50 ml.
  • There is a suggestion to find the new molarity of either substance after determining the total volume.

Areas of Agreement / Disagreement

Participants generally agree on the calculation of total volume at the equivalence point but do not reach a consensus on how to proceed with the calculations for pH or molarity.

Contextual Notes

Participants express uncertainty regarding the calculations needed to find the new concentration and pH at the equivalence point, indicating a reliance on definitions and mathematical steps that remain unresolved.

rcrx
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A 25.0 ml sample of 0.150 M HNO2 is titrated with a 0.150 M NaOH solution. What is the pH at the equivalence point? The Ka of HNO2 is 4.50x10-4


What I can't get is the fact I don't know how much has already been titrated at the equivalence point. So it's difficult to know the total volume to find the new concentration.

The answer is supposed to be pH = 8.11, and I could guess that with the titration of a weak acid with a strong base that the pH will rise a bit. But I can't presume how to do this mathematically.
 
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rcrx said:
What I can't get is the fact I don't know how much has already been titrated at the equivalence point. So it's difficult to know the total volume to find the new concentration.
If you are having trouble with this, you should take a step back ... and start at the definition of the equivalence point. What is the definition?
 
Both concentrations are in equal proportion and neither consumes the other. So that means there is 25.0 + 25.0 for a combined total of 50ml?
 
Correct. Now, what's the next step?
 
Find the new Molarity of either substance?
 

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