Question

The products formed when a pinch of sugar is strongly heated for fifteen minutes in a test tube are:
A. Carbon and water vapour
B. Carbon, hydrogen and oxygen
C. Carbon dioxide and water vapour
D. Carbon dioxide and hydrogen

Answer 1

To answer this question you need to recall the structure and reactions of sucrose (sugar). The sucrose molecule is made up of carbon, hydrogen and oxygen. Thus, on heating we may obtain breakdown products containing these elements.

Complete step by step solution:
When sugar is heated slowly and carefully, it transforms from a solid to liquid substance. On continued heating up to a temperature of ${200^{\circ}}{\text{C}}$, sugar loses water as water vapour, develops a different taste and smell, forming a brown amorphous mass called caramel.
On continued heating, the molecules in heated sucrose further break down and produce several different compounds. Its sweet taste is replaced by a more bitter flavour.
On decomposition of sucrose, water is lost as water vapour leaving behind along with carbon dioxide gas.
Thus, the products formed when a pinch of sugar is heated in a test tube are carbon dioxide and water vapour.

Thus, the correct option is C.

Additional information:

1. Sucrose is obtained from cane sugar and sugar beets. It is found in all photosynthetic plants.
2. Sucrose is a non-reducing sugar and is formed by condensation of one molecule of glucose and one molecule of sucrose.
3. Sucrose is a colourless, odourless crystalline compound with melting point of around 185 ⁰C.
4. It is very soluble in water, slightly soluble in alcohol and insoluble in ether.
5. It is dextro-rotatory but does not show mutarotation.

Note:
When sugar is heated, the molecules break down and re-form to a dark orange or brown compound with a characteristic flavour known as caramel.
Caramel is a confectionary product and is used as a flavouring in puddings, desserts, toppings for ice cream and custard. Caramel is used to prepare a variety of candies, desserts, toppings and confections.