Question

What is the main reason that it takes 2 to 3 minutes for the reaction to occur between sucrose and sulfuric acid in the dehydration of sucrose?

Answer 1

The are different reasons and these are the following:
1) The acid starts to go yellow as the dehydration begins.
2)The rate of dehydration then accelerates as the acid heats up .
3)This expands out of the reaction vessel.

Answer 2

There is a time delay of almost two to three minutes before the reaction proceeds because of the following processes:

1) The acid starts to go yellow as the dehydration begins.

2) The rate of dehydration then accelerates as the acid heats up because the reaction is exothermic/chemical (releases energy by light or heat). As the sugar molecules are stripped of water, the heat generated turns the water into steam which then expands the remaining carbon into a porous, smoking, black column.

3) This expands out of the reaction vessel, producing a choking acrid vapor and the smell of burned sugar.

At this stage, sulfuric acid is highly corrosive and will burn skin so one must avoid contact with it.