Sapling Learning Carboxylic acids are weak acids and dissociate in aqueous solut

Question

Sapling Learning Carboxylic acids are weak acids and dissociate in aqueous solution to the carboxylate anion. RCOOH aq ) RC00' (aq) + H"(aq) The extent of dissociation is given by the equilibrium dissociation constant, K, which is often expressed in its logarthmic form as pK. (The cation is written simply as H and is understood to be solvated with one or more water molecules in solution.) [H][RC001 pK,log, If a butyric acid/butyrate buffer is 0.030 M in butyric acid and has a pH of 4.93, what is the molar concentration of the butyrate ion? The pk, of butyric acid is 4.81. Number no Previous Give Up & View Solution e Check Answer 0 Next Exit 2-1 Hint

Explanation / Answer

Answer:

Henderson-Hasselbalch equation:

pH = pKa + log([CH3CH2CH2COO-]/[CH3CH2CH2COOH])

4.93 = 4.81 + log([CH3CH2CH2COO-]/0.030)

log([CH3CH2CH2COO-]/0.030) = 0.12

[CH3CH2CH2COO-]/0.030 = 10^0.12 = 1.3182

[CH3CH2CH2COO-] = 0.039 M

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