Answer to Question #101251 in General Chemistry for Sabrina

Question

To raise the temperature of boiling water, cooks will add salt to it.

Explain in terms of intermolecular forces why adding salt (NaCl) to water will raise the boiling point of water

Answer 1

When you add salt to water, sodium chloride dissociates into sodium and chlorine ions and these charged particles alter the intermolecular forces between water molecules.

In addition to affecting the hydrogen bonding between water molecules, there is an ion-dipole interaction to consider: Every water molecule is a dipole, which means one side (the oxygen side) is more negative and the other side (the hydrogen side) is more positive. The positively charged sodium ions align with the oxygen side of a water molecule, while the negatively charged chlorine ions align with the hydrogen side of a water molecule. The ion-dipole interaction is stronger than the hydrogen bonding between the water molecules, so more energy is needed to move water away from the ions and into the vapor phase. Thus boiling point increases.