Hint: Think of a decomposition reaction of sugar. Also, recall that sugar becomes brown when heated.
Complete step by step answer:
Commonly available sugar (table) is sucrose. It is a disaccharide containing two monomers glucose and fructose. Upon heat, sugar first melts. The physical state changes from solid to liquid. On further heating, sucrose breaks into glucose and fructose. Upon further heating to high temperature, water is lost. The individual components, glucose and fructose react with each other to produce several different compounds. These different compounds provide different flavour elements for caramel, such as butterscotch, nutty and toasty flavors. With increase in the temperature, the color of sugars darkens. The process is known as caramelisation.
When sugar is continuously heated at very high temperature, a black powdery substance is obtained. This substance is charred sugar. This process is a chemical change.
Sucrose is a carbohydrate (hydrate of carbon). The chemical formula of sucrose is \[{{\rm{C}}_{12}}{{\rm{H}}_{22}}{{\rm{O}}_{11}}\]. On heating, sucrose decomposes to carbon and water.
\[{{\rm{C}}_{12}}{{\rm{H}}_{22}}{{\rm{O}}_{11}} \to 12{\rm{ C + 11 }}{{\rm{H}}_2}{\rm{O }}\]
Water is lost as steam and only black ashes remains which contains carbon.
Note:
Caramelisation is browning of sugar. Caramelisation has widespread use in cooking to obtain brown colour and sweet nutty flavor.
