RI Mole Concept and Stoichiometry Notes 2025

-1- Raffles Institution Year 5 H2 Chemistry 2025 Supplementary Notes – The Mole Concept and Stoichiometry Content • Relative masses of atoms and molecules • The mole, the Avogadro constant • The calculation of empirical and molecular formulae • Reacting masses and volumes (of solutions and gases) Learning Outcomes [The term relative formula mass or Mr will be used for ionic compounds] Candidates should be able to: (a) define the terms relative atomic, isotopic, molecular and formula masses (b) define the term mole in terms of the Avogadro constant (c) calculate the relative atomic mass of an element given the relative abundances of its isotopes (d) define the terms empirical and molecular formula (e) calculate empirical and molecular formulae, using combustion data or composition by mass (f) write and/or construct balanced equations (g) perform calculations, including use of the mole concept involving: (i) reacting masses (from formulae and equations); (ii) volumes of gases (e.g. in the burning of hydrocarbons); (iii) volumes and concentrations of solutions. [when performing calculations, candidates’ answers should reflect the number of significant figures given or asked for in the question] (h) deduce stoichiometric relationships from above calculations such as those in (g) Lecture Outline References 1 Atoms and Sub-atomic Particles 1 Cambridge International AS and A Level Chemistry (by Peter Cann and Peter Hughes) 2 Cambridge International AS and A Level Chemistry Coursebook with CD-ROM (by Lawrie Ryan and Roger Norris) 3 A Level Chemistry 4ed (by E. N. Ramsden) 4 Chemistry in Context 6ed (by Graham Hill and John Holman) 5 Chemistry – The Molecular Nature of Mater and Change (by Silberberg) 6 https://www.chemguide.co.uk 2 Relative Masses 3 The Mole and Related Concepts 4 Empirical and Molecular Formulae 5 Stoichiometry 6 Reacting Volumes of Gases 7 Concentration of a Solution 8 Acid-Base Titrations

-2- 1 Atoms and Sub-atomic Particles 1.1 The sub-atomic particles • An atom is the smallest part of an element which can ever exist, whereas a molecule is the smallest part of an element or a compound which can exist alone under ordinary conditions. • A ll atoms are composed of three fundamental particles  protons, neutrons and electrons. Sub-atomic particle proton neutron electron Symbol 1 1p 1 0 n 0 1e− Relative mass 1 1 1 1840 Relative charge +1 0 –1 Location within the atom in the nucleus in the nucleus around the nucleus 1.2 Important terms and definitions Term Symbol Definition (a) proton number or atomic number Z • The proton number (or atomic number) of an element is the number of protons in the nucleus of an atom of that element. • The atomic number determines the identity of an atom. For example, every atom with an atomic number of 6 is a carbon atom; it contains 6 protons in its nucleus. (b) nucleon numb