Titration of Nitrous Acid with Sodium Hydroxide

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SUMMARY

The titration of 25.0 ml of 0.150 M nitrous acid (HNO2) with 0.150 M sodium hydroxide (NaOH) reaches an equivalence point where the pH is calculated to be 8.11. At this point, the total volume of the solution is 50.0 ml, as both the acid and base are present in equal proportions. The key to determining the pH lies in understanding that the weak acid HNO2 has a dissociation constant (Ka) of 4.50x10-4, which influences the resulting pH after titration. The new molarity of the resulting solution must be calculated to find the pH accurately.

PREREQUISITES
  • Understanding of acid-base titration concepts
  • Knowledge of weak acid dissociation and its equilibrium constant (Ka)
  • Familiarity with calculating molarity and solution concentrations
  • Basic grasp of pH calculations and the pH scale
NEXT STEPS
  • Calculate the new molarity of the resulting solution after titration
  • Learn about the Henderson-Hasselbalch equation for pH calculations
  • Study the concept of equivalence points in titrations
  • Explore the behavior of weak acids and strong bases in titration scenarios
USEFUL FOR

Chemistry students, laboratory technicians, and anyone involved in analytical chemistry or titration experiments will benefit from this discussion.

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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