Unit 3
Reactions and stoichiometry
A chemical equation is an exact recipe: atoms are neither made nor lost, and the coefficients give the ratio of particles. In this unit you write formulas from the charges of ions and name compounds, balance equations, use mole ratios to calculate masses of reactants and products, find the limiting reagent that runs out first, calculate with concentrations and volumes in solution, and predict whether mixing two solutions gives a precipitate, a gas or water.
- 1 Naming ions and compounds Charge balance fixes the formula and the formula fixes the name. Learn the charges of ions and the common polyatomic ions, the hypo-, -ite, -ate and per- of oxoanions, and the number prefixes of molecular compounds. 35 min
- 2 Balancing chemical equations Conservation of atoms is the only rule: balance by inspection, then write balancing as linear equations and watch the exact solution come out in smallest whole numbers. 25 min
- 3 Mole ratios and mass calculations Coefficient ratios are mole ratios. Follow the grams → moles → moles → grams road to find how much carbon dioxide one kilogram of petrol makes. 25 min
- 4 Limiting reagents and yield Adjust the reactants in the reaction mixer, see which runs out first and how much is left, and work out the theoretical and percent yield. 30 min
- 5 Solution stoichiometry: concentration, dilution and titration Molarity, C₁V₁ = C₂V₂, preparing a standard solution step by step on a virtual bench, and finding an unknown concentration from titration data. 30 min
- 6 Reactions in aqueous solution Electrolytes and ions; the three driving forces — precipitate, gas, water; molecular, complete ionic and net ionic equations; the activity series and displacement. 35 min