How to Calculate Buffer Volume for Given pH and Concentrations

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SUMMARY

The discussion centers on calculating the buffer volume required to achieve a specific pH using a 3.00 M HCO3- solution and a 0.200 M CO32- solution. The correct volume to be added is determined to be 13.96 mL. The calculation utilizes the Henderson-Hasselbalch equation, where pKa is given as 5.6e-11. The user initially miscalculated the required volume as 11.93 mL, indicating a misunderstanding in applying the mole ratios in the context of buffer solutions.

PREREQUISITES
  • Understanding of the Henderson-Hasselbalch equation
  • Knowledge of buffer solution chemistry
  • Familiarity with pKa values and their significance
  • Basic skills in stoichiometry and mole calculations
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  • Review the Henderson-Hasselbalch equation in detail
  • Study buffer solution preparation techniques
  • Learn about the significance of pKa in buffer systems
  • Practice stoichiometric calculations involving acid-base reactions
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Chemistry students, educators, and laboratory technicians involved in buffer preparation and pH management in chemical experiments.

Fibonacci
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am really stuck on this problem, can't seem to get to the right answer

Homework Statement

How many mL of a 3.00 M HCO3- solution must be added to 200 mL of a 0.200 M CO32- solution to make a buffer with pH = 10.30?

Answer. 13.96 mL

Homework Equations



pKa + log([base]/[acid])=pH

HCO3(-) --> H+ + CO3 (2-)

The Attempt at a Solution



pKa + log([base]/[acid])=pH
pH=10.3
pKa= 5.6e-11 (this value is give to us in our book)

0.048188 = log([base]/[acid])
1.117=[base/acid]

since the final volume cancels
we simply just use the mole ratios
let x be the mL of HCO3 - needed

base= (0.20)(0.2)
acid= 3x

1.117=0.2(0.2)/3x

x=11.933ml, which is way different to the actual answer
would appreciated heaps if someone could help
thanks
 
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Must be error in the answer (or some typo in the data), 11.93mL seems to be correct.

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