Question

Write a balanced chemical reaction for the dehydration of concentrated sulphuric acid with sugar crystals.

Answer 1

Hint: Concentrated sulphuric acid is also known as a dehydrating agent. This is because it removes the water molecule from the compound to which it is added. The addition of water molecules to compounds is known as hydration while the removal of water molecules from that compound is known as dehydration.

Complete answer:
When we add water molecules to a compound then it is known as hydration of the compound. It is done by adding aqueous \[{H_2}O\] , whereas when we remove water molecules from the compound it is known as dehydration of the compound. It is done by using concentrated sulphuric acid. Such an agent which is used to remove water molecules is known as a dehydrating agent. Since we know that the molecular formula of sugar is \[{C_{12}}{H_{22}}{O_{11}}\] . Since it contains water molecules, therefore it will be dehydrated by removing all water molecules from sugar. This can be represented with the help of chemical equation as,
 \[{C_{12}}{H_{22}}{O_{11}}{\text{ + n}}{{\text{H}}_2}{\text{S}}{{\text{O}}_4}{\text{ }}\xrightarrow{{}}{\text{ 12C + 11}}{{\text{H}}_2}{\text{O + n}}{{\text{H}}_2}{\text{S}}{{\text{O}}_4}\]
When we add sugar molecules with n-mole of concentrated sulphuric acid then we get twelve moles of carbon atom and 11 moles of water molecule, n-moles of sulphuric acid. Thus it behaves like a catalyst, it does not take part in reaction. We get carbon as a spongy substance after dehydration of sugar.

Note:
The number of moles of concentrated sulphuric acid remains conserved during reaction. Thus it behaves like a dehydrating agent by removing all water molecules from sugar. If a compound does not contain water molecules then concentrated sulphuric acid is used to bring unsaturation in the given compound.