Question

Charring of sugar is due to:
A.Oxidation
B.Reduction
C.Dehydration
D.Reduction and hydration

Answer 1

Hint: Sugar charring is when sugar is continuously heated in a dish, then it starts evaporating and becomes foggy due to water vapour. A black powdery substance is left behind, which is charcoal. It is a chemical change as it cannot be reversed.

Complete answer:
The charring of sugar takes place when treated with concentrated sulphuric acid. Dehydration reaction is the type of reaction involved in it. Thus when sugar loses a molecule of water, it gets charred. The acid starts to go yellow as the dehydration begins. The rate of dehydration then accelerates as the acid heats up because the reaction is exothermic. 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. This expands out of the reaction vessel, producing a choking acrid vapour and the smell of burned sugar. At this stage I normally remind my students that sulfuric acid is highly corrosive and will burn skin so they must avoid contact with it.
So, the correct answer is (C) dehydration.

Note:
Charring means partially burning so as to blacken the surface. Charring can result from naturally occurring processes like fire; it is also a deliberate and controlled reaction used in the manufacturing of certain products. The mechanism of charring is part of the normal burning of certain solid fuels like wood.