Primary standard solutions are prepared from substances that are pure, stable, water-soluble and have a high molar mass. Ideally, a standard substance shouldn’t be toxic or expensive. You can make a primary standard by weighing exactly one molar mass of a standard substance and dissolving it in one litre of pure water to get a concentration of one mole. This process is known as the weighing method. You can prepare a secondary standard solution by following what’s known as the dilution method. In this method, a primary standard solution is used to calibrate the secondary standard solution. A secondary standard can also be directly prepared from a primary standard solution.