Salt dissolves in water because of how water's molecules are built and how ionic compounds like salt interact with them. Here’s a concise, clear explanation. core idea
- Salt (sodium chloride, NaCl) is an ionic compound: sodium ions (Na+) and chloride ions (Cl−) held together by strong electrostatic (ionic) attractions.
- Water is a polar molecule: one end is slightly positive (the hydrogen side) and the other end is slightly negative (the oxygen side).
What happens when salt meets water
- The positive end of water is attracted to the negatively charged chloride ions, and the negative end of water is attracted to the positively charged sodium ions.
- These favorable interactions are strong enough to overcome the attractions that hold Na+ and Cl− together in the solid lattice.
- As water molecules surround individual Na+ and Cl− ions, the ions are pulled away from the crystal and dispersed throughout the water, forming a solution of hydrated ions: Na(H2O)6+ and Cl−(H2O)n in many cases.
Key factors
- Polarity: Water’s polarity drives ion-dipole interactions with dissolved ions, stabilizing them in solution.
- Hydrogen bonding and dielectric effect: Water’s hydrogen-bonding network and high dielectric constant reduce the electrostatic energy between ions, aiding dissolution.
- Temperature and amount of water: Higher temperature generally increases solubility for many salts, and sufficient water is required to accommodate all ions.
Why water can dissolve many salts
- Many salts are ionic compounds like NaCl; the same ion-dipole interactions with water apply, so they dissolve as long as the lattice energy of the solid isn’t too high relative to the hydration energy of the ions and the available solvent.
What about salts that don’t dissolve well
- Some salts have very high lattice energies or form less favorable hydration with water, so they precipitate or remain solid in water. In such cases, dissolution is limited by thermodynamics and kinetics.
If you’d like, I can tailor this to a specific salt or add a simple energy- relationship explanation (lattice energy vs hydration energy) with numerical examples.
