JEE Advanced 2013 · Paper 1 · Chemistry Q35

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ChemistryMultiple correct+4 / -1Question 35 of 60

The initial rate of hydrolysis of methyl acetate (1 M) by a weak acid (HA, 1 M) is 1/100 $^\text{th}$ of that of a strong acid (HX, 1 M), at 25 °C. The $K_a$ of HA is

1\times10^{-4}

1\times10^{-5}

1\times10^{-6}

1\times10^{-3}

Answer and worked solution

Official answer: A

Rate ∝ [H⁺]. The weak acid gives $\frac1{100}$ of the strong acid's $[\ce{H+}]=1$ M, i.e. 0.01 M.

Ka. $[\ce{H+}]=\sqrt{K_aC}$ gives $10^{-4}=K_a\times1$ , so $K_a=1\times10^{-4}$ .

(A)

Topics:pH and ionisation Rate of reaction and rate law

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JEE Advanced 2013 · Paper 1, Chemistry question 35