Note:

IGCSE Chemistry Notes on Stoichiometry for  2026/2027 /2028 

Syllabus Content:

3.1 Formulae

Core

1. State the formulae of the elements and compounds named in the subject content 
2. Define the molecular formula of a compound as the number and type of different atoms in one molecule 
3. Deduce the formula of a simple compound from the relative numbers of atoms present in a model or a diagrammatic representation 
4. Construct word equations and symbol equations to show how reactants form products, including state symbols

Supplement 

1. Define the empirical formula of a compound as the simplest whole number ratio of the different atoms or ions in a compound 
2. Deduce the formula of an ionic compound from the relative numbers of the ions present in a model or a diagrammatic representation or from the charges on the ions 
3. Construct symbol equations with state symbols, including ionic equations 
4. Deduce the symbol equation with state symbols for a chemical reaction, given relevant information

3.2 Relative masses of atoms and molecules

Core

1. Describe relative atomic mass, Ar , as the average mass of the isotopes of an element compared to 1/12th of the mass of an atom of 12C 
2. Define relative molecular mass, Mr , as the sum of the relative atomic masses. Relative formula mass, Mr , will be used for ionic compounds 
3. Calculate reacting masses in simple proportions. Calculations will not involve the mole concept

3.3 The mole and the Avogadro constant

Core 

1. State that concentration can be measured in g/dm3 or mol/dm3

Supplement 

1. State that the mole, mol, is the unit of amount of substance and that one mole contains 6.02 × 1023 particles, e.g. atoms, ions, molecules; this number is the Avogadro constant 
2. Use the relationship amount of substance (mol) = mass (g) molar mass (g/mol) to calculate: (a) amount of substance (b) mass (c) molar mass (d) relative atomic mass or relative molecular/formula mass (e) number of particles, using the value of the Avogadro constant 
3. Use the molar gas volume, taken as 24dm3 at room temperature and pressure, r.t.p., in calculations involving gases
4. Calculate stoichiometric reacting masses, limiting reactants, volumes of gases at r.t.p., volumes of solutions and concentrations of solutions expressed in g/dm3 and mol/dm3 , including conversion between cm3 and dm3 
5. Use experimental data from a titration to calculate the moles of solute, or the concentration or volume of a solution 
6. Calculate empirical formulae and molecular formulae, given appropriate data 
7. Calculate percentage yield, percentage composition by mass and percentage purity, given appropriate data

Happy Learning,

Team,

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