Chemistry

A mole is a counting unit for particles, defined as exactly 6.022×10²³ entities (Avogadro’s number) of atoms, molecules, or ions. Chemists use it because atoms are far too small and numerous to count individually. One mole of a substance has a mass in grams equal to its molar mass.

The pH scale runs from 0 to 14 and measures how acidic or basic a solution is, based on hydrogen-ion concentration. A pH of 7 is neutral, values below 7 are acidic, and values above 7 are basic. Each whole-number step is a tenfold change, so pH 4 is ten times more acidic than pH 5.

Balancing means adjusting the coefficients in front of formulas so that each element has the same number of atoms on both sides, satisfying the conservation of mass. You change only the coefficients, never the subscripts within a formula. The goal is the smallest set of whole-number coefficients that makes atoms equal on both sides.

Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). You calculate it by adding the atomic masses of every atom in the chemical formula. For water (H₂O), that is 2×1.008 + 16.00 ≈ 18.02 g/mol.