NJC 1 Mole Concept _ Stoichiometry

National Junior College SH1 Chemistry 1 (I) 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 required for H2 (9729) and H1 (8873) Chemistry: [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 mass, based on the 12C scale; (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 no. of significant figures given or asked for in the question] (h) Deduce stoichiometric relationships from calculations such as those in (g). THE MOLE CONCEPT AND STOICHIOMETRY All Rights Reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording or any other information storage and retrieval system, without prior permission in writing from the copyright owner. Copyright © 2023 National Junior College

National Junior College SH1 Chemistry 2 1. RELATIVE MASSES OF ATOMS AND MOLECULES Success Criteria: • Able to define the terms relative atomic , isotopic, molecular and formula mass, based on the 12C scale. • Able to calculate the relative atomic mass of an element given the relative abundances of its isotopes. 1.1 Relative Atomic Mass Scale: The Carbon–12 scale Atoms are too small to be weighed directly and it is inconvenient to express masses of individual atoms in terms of kilograms , kg, or grams, g (e.g. mass of one H atom = 1.67 × 10–27 kg). It is more practical to consider its mass relative to that of another atom known as the standard. The most abundant isotope of carbon, 12C, is the chosen standard. In this scale, a n atom of carbon –12 is assigned a mass of exactly 12 atomic mass units (a.m.u). 1.1.1 Relative Isotopic Mass (NO UNITS) Isotopes are atoms of the same element whose nuclei