Theoretical pH of HOAc + NaOAc Solution

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SUMMARY

The theoretical pH of a solution containing 30.00 mmol of acetic acid (HOAc) and 53.00 mmol of sodium acetate (NaOAc) can be calculated using the Henderson-Hasselbalch equation. NaOAc acts as the conjugate base of HOAc, not a strong base. The correct approach involves using the concentrations of the conjugate base and conjugate acid to avoid negative logarithmic values. This method ensures accurate pH calculations in buffer solutions.

PREREQUISITES
  • Understanding of the Henderson-Hasselbalch equation
  • Knowledge of weak acids and their conjugate bases
  • Familiarity with stoichiometry in acid-base reactions
  • Basic skills in logarithmic calculations
NEXT STEPS
  • Study the Henderson-Hasselbalch equation in detail
  • Learn about buffer solutions and their pH calculations
  • Explore the properties of weak acids and their conjugate bases
  • Practice stoichiometric calculations in acid-base chemistry
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Chemistry students, educators, and anyone involved in acid-base chemistry or buffer solution preparation will benefit from this discussion.

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Homework Statement


Calculate the theoretical pH of each solution. The first solution was 30.00 mmol of HOAc (acetic acid) and 53.00 mmol of NaOAc. There was no water in this solution.

Homework Equations



We have to use this equation.
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The Attempt at a Solution



I'm unsure of what to plug in. I know HOAc is the weak acid and NaOAC is the strong base? But if I only plug those two numbers I'd have a negative number and you can't take the log of a negative number.
 
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NaOAc is not the strong base, it is a conjugate base of AcOH (or HOAc as you wrote it).

Equation you have to use... sigh. Another way of isolating students from understanding the chemistry behind the calculation. You need to have concentration (or number of moles) of conjugate base in the nominator and concentration (or number of moles) of the conjugate acid in the denominator. What you have there now is just a way of calculating numbers of moles from the stoichiometry of the neutralization/protonation reactions.
 

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