Question

Which observable property is used in the kinetic study of the following first order reaction and why?

\[\ce{C12H22O11 + H2O ->[H+] C6H12O6 + C6H12O6}\]

Answer 1

1. In the kinetic study of the acid-catalysed hydrolysis of sucrose \[\ce{C12H22O11 + H2O ->[H+] C6H12O6 + C6H12O6}\] optical rotation (measured using a polarimeter) is used.
2. Sucrose, glucose, and fructose are all optically active sugars, but sucrose is dextrorotatory, glucose is dextrorotatory and fructose is levorotatory and has a greater magnitude of rotation than glucose.
3. As the reaction proceeds, the net optical rotation of the solution changes from positive to negative due to the formation of fructose in a larger optical effect.
4. The change in angle of rotation (α) is proportional to the concentration of sucrose decomposed at any time.
5. Therefore, by measuring the angle of rotation at various times, the rate of the reaction can be calculated using the first-order rate law
   \[\ce{k = \frac{2.303}{t} log_10 (\frac{\alpha_0 - \alpha_\infty}{\alpha_1 - \alpha_\infty})}\]