Chapter 14.3, Problem 1RQ

Interpretation Introduction

Interpretation: The different in salt and sugar despite being crystalline solids needs to be explained.

Concept introduction: A crystalline solid characterized by regular arrangement of its components. There are many types of crystalline solids such as ionic solids, molecular solids, covalent network solids, and metallic solids.

Answer to Problem 1RQ

The difference between salt and sugar arises because former is ionic solid and later is molecular solid.

Explanation of Solution

Common salt ( $NaCl$ ) is an ionic solid that contains positively charged $N{a}^{+}$ and negatively charged $C{l}^{-}$ and crystallizes in face centered cubic (FCC) lattice. When solid sodium chloride ( $NaCl$ ) dissolves in water, sodium ions ( $N{a}^{+}$ ) and chloride ions ( $C{l}^{-}$ ) are dispersed throughout the solution. These ions are free to move in the solution and hence it conducts an electric current.

On the contrary, sugar is a molecular solid. In a molecular solid molecules are held by intermolecular forces like dipole-dipole, London dispersion force and hydrogen bonding.

Sugar consists of neutral molecules ( $C_{12}{H}_{22}{O}_{11}$ ) that are dispersed throughout the water when the solid dissolves, since no ions are present, and the resulting solution does not conduct electricity.

Conclusion

The difference between salt and sugar arises because former is ionic solid and later is molecular solid.