AI Tutor
If a forensic chemist discovers an unidentified white crystal at a scene, they cannot simply look through a microscope and count the atoms.
Instead, they destroy a small measured sample by heating or burning it, measuring the exact masses of the resulting elements to determine the compound's empirical formula—the simplest whole-number ratio of atoms in a substance.
How do we convert raw balance readings in grams into these fundamental atomic ratios?

The 4-Step Empirical Roadmap

In 1814, Swedish chemist Jöns Jacob Berzelius demonstrated that elements always combine in fixed proportions by mass based on their individual atomic weights.
Because equal masses of different elements contain different numbers of atoms, we must convert mass into moles—a counting unit equal to 6.022×10236.022 \times 10^{23} particles—by dividing each mass by the element's molar mass (MM), which is the mass in grams of one mole of that element.
Let's apply this core strategy to an experiment where elements combine directly.

Worked Example: Direct Combination of Masses

A student heats 4.86 g4.86\text{ g} of magnesium ribbon in a crucible until it completely reacts with atmospheric oxygen, producing 8.06 g8.06\text{ g} of pure magnesium oxide.
By the law of conservation of mass, the mass of oxygen consumed must be the total product mass minus the starting magnesium mass: mO=8.06 g−4.86 g=3.20 g Om_\text{O} = 8.06\text{ g} - 4.86\text{ g} = 3.20\text{ g}\text{ O}