Why Impurities Affect Melting Points

⚙️ Why Impurities Affect Melting Points

Imagine a pure crystal of salt as a perfectly ordered grid of sodium and chloride ions, all held together by equally strong electrostatic forces. Now drop in some "wrong size" particles (the impurity). They don't fit neatly into the grid — they create weak spots and distort the lattice structure. These weak spots require less energy to break, so the crystal starts melting at a lower temperature than normal.

For boiling, impurity particles dissolved in the liquid interfere with solvent molecules trying to escape to the gas phase. They need extra energy to escape — hence the boiling point rises. This is why salt is added to cooking water: it genuinely raises the boiling point slightly (though not enough to cook faster in any meaningful way!).

The broader the melting range, the more impurities are present. Pharmaceutical companies use melting point data as a quick purity check before releasing drug products.