EJC 2023 The Mole Concept and Stoichiometry Lecture Notes Students (1)

2023 JC1 H2 CHEMISTRY (9729) CORE IDEA 3: TRANSFORMATION Topic 1: THE MOLE CONCEPT & STOICHIOMETRY Name: ___________________________________________ Civics Group: _________ The use of the Data Booklet is relevant for this topic. Please have a copy with you as you attend the lectures. Please note that Sections 1, 2, 3, 4.1 , 5.2 & 5.3 involve concepts which have been covered at the secondary school level. Please read through these areas on your own and refresh your concepts before the lectures. Another independent study segment, Section 6.7, will be covered in greater detail in your practicals or later topics. [the term relative formula mass or Mr will be used for ionic compounds] Students should be able to: (a) define the terms relative atomic, isotopic, molecular and formula mass (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 calculations such as those in (g) From the topics of Electrochemistry & Transition Elements Chemistry: (i) describe and explain redox processes in terms of electron transfer and/or of changes in oxidation number (oxidation state); (j) construct redox equations using the relevant half-equations (k) describe and exp lain the use of Fe 3+/Fe2+, MnO4–/Mn2+ and Cr2O72–/Cr3+ as examples of redox systems REFERENCES 1. Chemistry (for CIE AS & A Level) by Peter Cann & Peter Hughes (540 CAN) 2. Chemistry: The Molecular Nature of Matter & Change by Martin S. Silberberg (540 SIL) 3. Calculations in A Level Chemistry (4th Edition) by E.N. Ramsden 4. Calculations for AS/A Level Chemistry by Jim Clark

T h e M o l e C o n c e p t & S t o i c h i o m e t r y E u n o i a J u n i o r C o l l e g e 2 | P a g e LECTURE CONTENT 1 Relative Masses of Atoms and Molecules (INDEPENDENT STUDY) ................................ .... 3 1.1 Relative Isotopic Mass (no unit) ................................ ................................ .......................... 3 1.2 Relative Atomic Mass (symbol: Ar, no unit) ................................ ................................ ......... 4 1.3 Relative Molecular Mass (symbol: Mr, no unit) ................................ ................................ .... 5 1.4 Relative Formula Mass (symbol: Mr, no unit) ................................ ................................ ...... 5 2 The Mole and Related Concepts (INDEPENDENT STUDY)................................ .................... 6 2.1 The Mole and Avogadro constant ................................ ................................ ....................... 6 2.2 Molar Mass ................................ ................................ ................................ ......................... 8 2.3 Molar Volume of Gas ................................ ................................ ................................ .......... 8 2.4 Molar concentration ................................ ................................ ................................ ............ 9 3 Empirical and Molecular Formulae (INDEPENDENT STUDY) ................................ ............. 10 3.1 Definitions ................................ ................................ ................................ ......................... 10 3.2 Calculations using percentage composition by mass ................................ ........................ 11 3.3 Calculations using combustion data ................................ ................................ .................. 12 4 Stoichiometry ................................ ................................ ................................ ......................... 13 4.1 Quantitative Information from a Balanced Equation ................................ .......................... 13 4.2 Limiting Reagent ................................ ................................ ................................ ............... 13 4.3 Percentage Yield ................................ ................................ ................................ .............. 14 4.4 Calculations on Combustion Reactions ................................ ................................ ............. 16 5 Volumetric Analysis (VA) ................................ ................................ ................................ ...... 21 5.1 Acid-Base Titrations (will be covered in detail in Acid-base equilibria) .............................. 21 5.2 Calculations on Acid-Base Reactions (INDEPENDENT STUDY) ................................ ...... 23 5.3 Dilution of Solutions (INDEPENDENT STUDY) ................................ ............................... 25 5.4 Back-Titrations ................................ ................................ ................................ .................. 26 6 Redox Reactions ................................ ................................ ................................ .................... 29 6.1 Definitions of oxidation and reduction ................................ ................................ ............... 29 6.2 Common Oxidising and Reducing Agent ................................ ................................ .......... 30 6.3 Oxidation Numbers ................................ ................................ ................................ ........... 31 6.4 Disproportionation ................................ ................................ ................................ ............ 34 6.5 Balancing Half- Equations for Redox Reactions ................................ ................................ 35 6.6 Determination of oxidation numbers using half-equation ................................ ................... 38 6.7 Redox Titrations and Calculations ................................ ................................ .................... 43 APPENDIX ................................ ................................ ................................ ................................ ..... 49 Appendix 1 – Double Indicator Titrations ................................ ................................ .................. 49 Appendix 2 – Relevance of Redox Reactions in our daily lives ................................ ................ 52

T h e M o l e C o n c e p t & S t o i c h i o m e t r y E u n o i a J u n i o r C o l l e g e 3 | P a g e 1 Relative Masses of Atoms and Molecules (INDEPENDENT STUDY) Relative Atomic Mass Scale: Carbon–12 scale • Atoms are too light to be weighed directly. Instead, chemists compare the masses of atoms with the masses of a standard atom: Carbon–12 atom (IUPAC Agreement 1960). • On this relative atomic mass scale, a 12C atom is assigned a mass of 12 units and the relative masses of all other atoms are obtained by comparison with the mass of a 12C atom. Hence, 1 unit of this mass scale is equivalent to 1 12 of the mass of a 12C atom. 1.1 Relative Isotopic Mass (no unit) • Isotopes are atoms of the same element whose nuclei have the same number of protons but different number of neutrons. e.g : 35 17Cl and 37 17Cl , 79 35Br and 81 35Br . • The relative abundance of the isotopes refers to the percentage by mass of the isotopes as they are found in the naturally occurring element. Example: isotope relative isotopic mass relative abundance (%) 1