8. Write a balanced chemical equation for the reaction of a general acid (HA) wi
ID: 477668 • Letter: 8
Question
8. Write a balanced chemical equation for the reaction of a general acid (HA) with base (water). Derive the Henderson-Hasselbalch (HH) equation that describes this reaction. Rewrite the HH equation in another form using the same terms (i.e. rationalize the equation if the concentrations of acid and conjugate base are interchanged). 9. The p Ka of aliphatic alcohols is 16. The pKa of aliphatic carboxylic acids is 5. Using ethanol and ethanoic acid as specific examples of these two chemical classes, draw structures to explain this difference in acidity. a. Which specific structure is the strongest acid? Which specific structure is the strongest conjugate base?Explanation / Answer
8) HA + H2O -------------> H3O+ + A-
Henderson- Hasselbalch equation is
pH = pKa + log [conjugate base]/[acid]
= pKa + log [A-]/[HA]
pH = pKa + log [A-]/[HA]
------------------------------------------------------------------------
A- + H2O -------------> HA + OH-
Henderson- Hasselbalch equation is
pOH = pKb + log [conjugate acid]/[base]
= pKb + log [HA]/[A-]
pOH = pKb + log [HA]/[A-]
9) Carboxylic acids are more acidic than alcohols.
Due to the presence of electron withdrawing ester group -COO- , Carboxylic acids are more acidic than alcohols.
Hence,
a) Ethanoic acid is strongest acid than ethanol.
Ethanol is weak acid.
Weak acids have strong conjugate bases.
Hence,
Ethanol has strong conjugate base i.e C2H5O-
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