Chemical and Ionic Equilibrium - Result Question 86

####30. The initial rate of hydrolysis of methyl acetate (1M) by a weak acid (HA,1M) is 1/100 th of that of a strong acid (HX,1M), at 25C. The Ka(HA) is

(2013 Adv.)

(a) 1×104

(b) 1×105

(c) 1×106

(d) 1×103

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Solution:

  1. PLAN RCOOR+H2OH+RCOOH+ROH

Acid hydrolysis of ester is follows first order kinetics.

For same concentration of ester in each case, rate is dependent on [H+]from acid.

 Rate =k[RCOOR]

Also for weak acid, HAH++A

Ka=[H+][A][HA] ( Rate )HA=k[H+]HA ( Rate )HX=k[H+]HX ( Rate )HX=100( Rate )HA

Also in strong acid, [H+]=[HX]=1M

( Rate )HX( Rate )HA=100=[H+]HX[H+]HA=1[H+]HA [H+]HA=1100 HAH++A 100 (1x)xx Ka=[H+][A][HA]=0.01×0.010.99=1.01×104



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