LaPugh Discount Perfumes has accidentally leaked one of its raw ingredients, met
ID: 531715 • Letter: L
Question
LaPugh Discount Perfumes has accidentally leaked one of its raw ingredients, methylphenyl ester (MPE, also known phenyl acetate, CH_3-COO-C H) into a river. The following hydrolysis data are available for MPE (from Mabey and Mill, 1978). k_a = 7.7 times 10^-5 M^-1s^-1 k_b = 1.4 M^-1s^-1 k 6.7 times 10 s^-1 a. The river pH is 7.5. Which of the three hydrolysis processes is the most important at this pH? [Be sure to show a calculation that justifies your answer, but I am not looking for some particular concentration or rate, just identify the most important process.] b. what is the half-life of MPE in this system? c. If this river mixes downstream with another river and the pH drops to 6.3, what is the new half-life of MPE?Explanation / Answer
At pH 7.5, the hydrolysis would occur by,
b. neutral hydrolysis
a) the half-life = ln(2)/k
= ln(2)/6.7 x 10^-8 = 1.03 x 10^7 s
b) when pH drops to 6.3, the new half-life would be equal to the one at pH 7.5
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