Consider the following statements about pseudo first order reactions.
(A) In the hydrolysis of ethyl acetate, water is taken in large excess, so the concentration of water is not altered much during the reaction.
(B) The hydrolysis of ethyl acetate is in reality a first order reaction.
(C) The inversion of cane sugar is another example of a pseudo first order reaction.
(D) The inversion of cane sugar gives glucose and galactose.
(E) For the inversion of cane sugar, Rate = k[C12H22O11].
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (B) and (D) only
A pseudo first order reaction is a higher order reaction that obeys a first-order rate law, because one reactant (here water) is present in such large excess that its concentration hardly changes.
\( \displaystyle \ce{CH3COOC2H5 + H2O} \xrightarrow{\ce{H+}} \ce{CH3COOH + C2H5OH} \)
\( \displaystyle \underset{\text{Cane sugar}}{\ce{C12H22O11}} + \ce{H2O} \xrightarrow{\ce{H+}} \underset{\text{Glucose}}{\ce{C6H12O6}} + \underset{\text{Fructose}}{\ce{C6H12O6}} \)
(A) In the hydrolysis of ethyl acetate, water is taken in large excess, so the concentration of water is not altered much during the reaction. — Correct statement. With 0.01 mol of ester and 10 mol of water, 9.99 mol of water is still left when the reaction is over.
(B) The hydrolysis of ethyl acetate is in reality a first order reaction. — Incorrect statement. In reality it is a second order reaction; the concentrations of both ethyl acetate and water affect its rate. It only behaves as first order.
(C) The inversion of cane sugar is another example of a pseudo first order reaction. — Correct statement. Water is again in large excess.
(D) The inversion of cane sugar gives glucose and galactose. — Incorrect statement. Cane sugar gives glucose and fructose.
(E) For the inversion of cane sugar, Rate = k[C12H22O11]. — Correct statement. The water term does not appear because its concentration stays almost constant.
NCERT (2026-27 edition):
3.3.3 Half-Life of a Reaction – “Consider the hydrolysis of ethyl acetate which is a chemical reaction between ethyl acetate and water. In reality, it is a second order reaction and concentration of both ethyl acetate and water affect the rate of the reaction. But water is taken in large excess for hydrolysis, therefore, concentration of water is not altered much during the reaction.”
“Inversion of cane sugar is another pseudo first order reaction.”
\( \displaystyle \underset{\text{Cane sugar}}{\ce{C12H22O11}} + \ce{H2O} \xrightarrow{\ce{H+}} \underset{\text{Glucose}}{\ce{C6H12O6}} + \underset{\text{Fructose}}{\ce{C6H12O6}} \)
\( \displaystyle \text{Rate} = k[\ce{C12H22O11}] \)