Before you start

Analytical chemistry answers two questions about a sample: what's in it, and how much. Water labs, drug makers, refineries and crime labs all run on it. This lesson recaps what it uses from General chemistry so you can start here.

A mole is 6.022 × 10²³ particles, and molar mass is the mass of a mole in grams (water is 18 g/mol). Moles = mass ÷ molar mass. Molarity, M, is moles of dissolved substance per litre of solution, so moles = M × litres. Remember to turn millilitres into litres: 25.0 mL is 0.0250 L.

Diluting keeps the moles of solute the same, so C₁V₁ = C₂V₂. An acid gives away H⁺ and a base takes it or adds OH⁻; they neutralize each other, and pH = −log₁₀ of the H₃O⁺ concentration, so pH 3 is ten times more acidic than pH 4.

Scientific notation writes big and small numbers as a number between 1 and 10 times a power of ten: 0.00025 = 2.5 × 10⁻⁴ and 45,000 = 4.5 × 10⁴. Concentrations in analysis are often tiny, in mg/L (ppm, parts per million) or µg/L (ppb, parts per billion). µ (micro) means a millionth.