Question

We have learned in this chapter that many ionic solids dissolve in water as strong electrolytes, that is, as separated ions in solution. What properties of water facilitate this process?

Short answer

The polar nature of water molecules and their ability to form ion-dipole interactions with ions in the ionic solid play a crucial role in the dissolution process. These interactions enable the separation and hydration of ions, which stabilizes them in the solution, allowing ionic solids to dissolve as strong electrolytes.

Step-by-step solution

Understanding the water molecule structure

Water (H₂O) has a bent molecular geometry with an oxygen atom at the center and two hydrogen atoms attached to it. The oxygen atom is more electronegative than the hydrogen atoms, resulting in a polar covalent bond where the electrons spend more time closer to the oxygen atom. This makes the water molecule a polar molecule, having a partially positive charge (δ+) at the hydrogen atoms and a partially negative charge (δ-) at the oxygen atom.

Explaining how water interacts with ions in a solid

When an ionic solid is placed in water, the negatively charged oxygen atoms of water molecules are attracted to the positively charged ions (cations) in the solid, while the positively charged hydrogen atoms of water are attracted to the negatively charged ions (anions) in the solid. These interactions are called ion-dipole interactions and help separate the ions from their crystal lattice structure.

Understanding hydration and the dissolution of ionic solids

Once the ions are separated from the crystal structure, they become surrounded by water molecules. This process is known as hydration. Hydration stabilizes the ions in the solution and prevents them from rejoining the crystal lattice. The ion-dipole interactions of water with the ions help dissolve the ionic solid and cause it to dissociate into its separate ions. The dissociation creates a strong electrolyte, as each ion in the solid becomes solvated by water molecules, allowing them to move freely and conduct electricity.

Conclusion

The properties of water that facilitate the dissolution of ionic solids as strong electrolytes are its polar nature and the ion-dipole interactions between water molecules and the ions in the solid. These interactions allow for the separation and stabilization of ions in the solution, resulting in the formation of strong electrolytes.