This unit is the practical and numerical heart of chemistry, designed to give Foundation Tier students the essential tools needed to measure and predict the quantities of substances involved in chemical reactions. The course begins with the foundational calculation: determining the Relative Formula Mass ($\text{M}_r$) of simple compounds by summing up the atomic masses of all atoms present. This is immediately connected to the fundamental rule that governs all chemistry: the Law of Conservation of Mass, which asserts that the total mass of reactants must equal the total mass of products.
Building on these basics, students are introduced to the central counting unit in chemistry, the mole. Understanding the mole allows chemists to link the mass of a substance to its chemical amount, forming the basis for all practical calculations. This mole concept is then applied in two major areas: calculating the Concentration of Solutions (finding out how much solute is dissolved in a specific volume) and performing simple proportional calculations to determine Reacting Masses—predicting the amount of product that will be formed from a known mass of reactant.
Finally, the unit addresses the practical realities of the laboratory and industry. Students will conceptually explore the importance of the limiting reactant (the substance that runs out first and stops the reaction), and understand why the actual yield of a reaction is rarely $100\%$. The unit concludes with an introduction to Atom Economy, emphasizing its role in sustainable chemistry by choosing reactions that produce the least amount of waste and maximize the use of expensive raw materials. The overall goal is to build strong confidence in the core chemical calculations required for the Foundation Tier exam.
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