Calculating pH of Buffered Solutions: Do You Need a Ka/Kb Value?

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SUMMARY

The discussion centers on calculating the pH of buffered solutions, specifically the example of a 0.50 M C2H5NH2 and 0.25 M C2H5NH3Cl mixture. Participants clarify that to determine the pH, one must utilize the Kb value of C2H5NH2, which can typically be found in a pKa table or through a quick online search. The importance of having the correct Ka/Kb values is emphasized for accurate pH calculations in buffered solutions.

PREREQUISITES
  • Understanding of buffered solutions and their components
  • Knowledge of acid-base equilibrium concepts
  • Familiarity with Kb and Ka values
  • Ability to use pKa tables for calculations
NEXT STEPS
  • Research how to find Kb values for weak bases
  • Learn how to use the Henderson-Hasselbalch equation for pH calculations
  • Study the relationship between pKa and pKb
  • Explore examples of calculating pH for various buffered solutions
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Students in AP Chemistry, educators teaching acid-base chemistry, and anyone looking to deepen their understanding of pH calculations in buffered solutions.

Dpasi314
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Hello,
So as the end of the year comes to an end, AP Chemistry is getting increasingly more difficult to the point where I don't understand anymore. In our homework there is a questions asking to calculate the pH of a buffered solution. The only information it gives you is the chemical formula and the molarity. i.e
Calculate the pH of each of the following buffered solutions:
a. 0.50 M C2H5NH2/0.25 M C2H5NH3Cl

I'm not quite sure how I'm suppose to be able to figure out the pH without having a Ka/Kb value given? Is the question assuming that I need to know what the Ka/Kb value? Or am I missing something entirely?

Thanks for the help!
 
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Hi Dpasi314. Welcome to Physics Forums.

Do you know the name of the 0.5 M species? If so, have you tried Googling it? It should take less than a minute to find the Kb.

Chet
 
Perhaps you were given a pKa table? Or there is one in your book?
 

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