Question

Inversion of cane sugar (sucrose) is a pseudo-first-order reaction. Explain.

OR

The reaction,

Can it be of pseudo-first-order type?

Answer 1

The inversion of cane sugar (sucrose) is an acid catalysed hydrolysis reaction which can be represented as,

This is a bimolecular reaction. 

Hence, 

The true rate law for the reaction should be, 

Rate = k[C₁₂H₂₂O₁₁] [H₂O]. 

This shows that the reaction should be second order.

Since water (H₂O) is in large excess, its concentration remains constant and the rate depends only upon the concentration of cane sugar.

Rate = k[C₁₂H₂₂O₁₁]

Therefore,

The second order true rate law becomes first order rate law. 

Hence,

The inversion of cane sugar is a pseudo first order reaction.