Key concepts in chemistry Study Guide

Calculating masses of reactants and products from balanced chemical equations is fundamental in chemistry. It allows you to predict how much product will form from a given amount of reactant, or how much reactant is needed to produce a specific amount of product. The key steps involve finding the relative formula masses (Mr) of the compounds involved, converting the given mass to moles, using the molar ratio from the balanced equation to find the moles of the substance you want to calculate, and then converting those moles back to mass. This process relies on the law of conservation of mass, which states that no atoms are lost or gained in a chemical reaction; therefore, the total mass of reactants equals the total mass of products.

The concentration of a solution measures the amount of substance (solute) dissolved in a given volume of another substance (solvent) or solution. In chemistry, it's often expressed as mass per unit volume, specifically in grams per cubic decimetre (g dm⁻³). A cubic decimetre is equivalent to one litre (1 L = 1 dm³). To calculate concentration, you divide the mass of the solute (in grams) by the volume of the solution (in cubic decimetres). This calculation is fundamental for preparing solutions of specific strengths in laboratory and industrial settings, ensuring accuracy in experiments and processes. If the volume is given in cm³, it must first be converted to dm³ by dividing by 1000, as 1 dm³ = 1000 cm³.